Contents

Contributors List

Preface

Acknowledgments

About the Companion Website

Chapter 1 Basics of Structure and Function The Cell, Its Structure and Functions Energy Production

Functions of Dna and Rna

Embryology

Tissues

Directional Terms and Planes

Body Cavities

Chapter 2 Body Water: Properties,and Functions Physicochemical Properties of Solutions Distribution of Body Water Water Balance

Dehydration, Thirst, and Water Intake

Adaptation to Water Lack

Chapter 3 Blood and Its Functions

General Characteristics

Leukocytes

Erythrocytes

Fate of Erythrocytes

Iron Metabolism

Anemia and Polycythemia

Hemostasis: Prevention of Blood Loss Prevention of Blood Coagulation Tests for Blood Coagulation Plasma and Its Composition

Chapter 4 Nervous System

Structure of the Nervous System Organization of the Nervous System The Nerve Impulse and Its Transmission Reflexes

The Meninges and Cerebrospinal Fluid Central Nervous System Metabolism

Chapter 5 The Sensory Organs

Classification of Sensory Receptors Sensory Receptor Responses

Pain

Taste

Smell

Hearing and Equilibrium

Vision

Chapter 6 Endocrine System

Hormones

Pituitary Gland

Thyroid Gland

Parathyroid Glands

Adrenal Glands

Pancreatic Gland

Prostaglandins and Their Functions

Chapter 7 Bones, Joints, and Synovial Fluid

General Features of,The Skeleton

Bone Structure

Bone Formation

Bone Repair

Joints and Synovial Fluid

Chapter 8 Muscle

Classification

Arrangement

Skeletal-Muscle Harnessing

Microstructure of Skeletal Muscle

Skeletal-Muscle Contraction

Comparison of Contraction Among Muscle Types

Changes in Muscle Size

Chapter Q The Cardiovascular System

Heart and Pericardium

Blood Vessels

Lymphatic System

Spleen

Cardiac Contractility

Electrocardiogram

Heart Sounds

Heart Rate and Its Control

Blood Pressure

Blood Flow

Capillary Dynamics

Chapter 10 The Respiratory System

Respiratory Apparatus

Factors Associated with Breathing

Respiratory Pressures

Pulmonary Ventilation

Diffusion of Respiratory Gases

Oxygen Transport

Carbon Dioxide Transport

Regulation of Ventilation

Respiratory Clearance

Nonrespiratory Functions of the Respiratory System

Pathophysiology Terminology

Avian Respiration

Chapter 11 The Urinary System

Gross Anatomy of the Kidneys and Urinary Bladder

The Nephron

Formation of Urine

Glomerular Filtration

Tubular Reabsorption and Secretion

Countercurrent Mechanism

Concentration of Urine

Extracellular Fluid Volume Regulation

Aldosterone

Other Hormones with Kidney Association

Micturition

Characteristics of Mammalian Urine

Renal Clearance

Maintenance of Acid-Base Balance

Avian Urinary System

Chapter 12 Digestion and Absorption

Introductory Considerations

The Oral Cavity and Pharynx

The Simple Stomach

Intestines

Accessory Organs

Composition of Foodstuffs

Pregastric Mechanical Functions

Gastrointestinal Motility

Mechanical Functions of the Stomach and Small Intestine

Mechanical Functions of the Large Intestine

Digestive Secretions

Digestion and Absorption

The Ruminant Stomach

Characteristics of Ruminant Digestion

Chemistry and Microbiology of the Rumen

Ruminant Metabolism

Avian Digestion

Chapter 13 Body Heat and Temperature Regulation

Body Temperature

Physiologic Responses,to Heat

Physiologic Responses,to Cold

Hibernation

Hypothermia and Hyperthermia

Chapter 14 Male Reproduction

Testes and Associated Structures

Descent of the Testes

Accessory Sex Glands,and Semen

Penis and Prepuce

Muscles of Male Genitalia

Blood and Nerve Supply

Spermatogenesis

Erection

Mounting and Intromission

Emission and Ejaculation

Factors Affecting Testicular Function

Reproduction in the Avian Male

Chapter 15 Female Reproduction

Functional Anatomy of the Female Reproductive System

Hormones of Female Reproduction

Ovarian Follicle Activity

Sexual Receptivity

Estrous Cycle and,Related Factors

Pregnancy

Parturition

Involution of the Uterus

Reproduction in the Avian Female

Chapter 16 Lactation

Functional Anatomy of Female Mammary Glands

Mammogenesis

Lactogenesis and Lactation

Composition of Milk

Milk Removal and Other Considerations

Appendix A Normal Blood Values

Appendix B Answers to Self Evaluation

Index

EULA

Chapter 2

Table 2-1

Table 2-2

Table 2-3

Table 2-4

Chapter 3

Table 3-1

Table 3-2

Table 3-3

Table 3-4

Chapter 4

Table 4-1

Table 4-2

Chapter 7

Table 7-1

Table 7-2

Chapter 9

Table 9-1

Table 9-2

Table 9-3

Chapter 10

Table 10-1

Table 10-2

Chapter 11

Table 11-1

Table 11-2

Table 11-3

Table 11-4

Chapter 12

Table 12-1

Table 12-2

Chapter 13

Table 13-1

Chapter 15

Table 15-1

Table 15-2

Table 15-3

Table 15-4

Chapter 16

Table 16-1

Appendix A

Table A-1

Table A-2

Table A-3

Table A-4

Table A-5

Table A-6

List of Illustrations

Chapter 1

Figure 1-1 Schematic drawing of the general organization of a cell.

Figure 1-2 Catabolism of proteins, fats, and carbohydrates resulting in the release of energy.,Stage 3, via the electron transfer chain, provides for the oxidative phosphorylation of adenosine diphosphate (ADP) and the production of a high-energy substance, adenosine triphosphate (ATP). This is the location of oxygen consumption by the body and production of metabolic water. (Adapted from Nelson DL, Cox MM. Lehninger Principles of Biochemistry. 3rd edn. New York: Worth Publishers, 2000.)

Figure 1-3 Two polynucleotide chains constitute the double helix of the DNA molecule. Obligatory base pairing occurs between A (adenine) and T (thymine), and also between G (guanine) and C (cytosine). The chains are held together by hydrogen bonding between bases. Histone proteins form a core between the nucleotide chains.

Figure 1-4 Replication of DNA. Coiling around histone proteins is loosened and the double helices split at a point of junction of complementary bases. The separate strands serve as a template for formation of its complementary base. Two new double-helix chromosomes formed where only one was before. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2009.)

Figure 1-5Diagrammatic representation of the stages of mitosis. See text for details. (From Cormack DH. Ham’s Histology. 9th edn. Philadelphia, PA: JB Lippincott Company, 1987.)

Figure 1-6 A schematic summary of genetic coding and its role in protein synthesis and related cell functions.

Figure 1-7Schematic diagrams of fertilization. Meiosis in spermatozoa and oocytes (division of chromosome numbers by one-half) occurs while in respective male and female reproductive systems. Entrance of a spermatozoon into an oocyte is followed by fusion of respective pronuclei to form a zygote with a proper chromosome number (2n or diploid). Cell division will proceed by mitosis to form a new individual.

Figure 1-8 Continued mitotic division from zygote to blastula. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley- Blackwell, 2009.)

Figure 1-9 The formation of the germ layers, ectoderm, mesoderm, and endoderm. A. Embryo embeds in the wall of the uterus. B. Formation of epiblast and hypoblast layers. The amniotic cavity is formed dorsal to the epiblast, and the hypoblast cells migrate to line the cavity of the blastula (blastocele), which becomes endoderm. C. Embryo viewed from above. The primitive streak is a thickening of epiblast cells on the longitudinal axis that migrate toward the primitive streak and become ectoderm. D. Cross-section through the region of the primitive streak showing migration of cells between ectoderm and endoderm that become mesoderm. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2009.)

Figure 1-10 Epithelial tissue classifications. The epithelial cells are shown lying on a noncellular basement membrane that serves an adhesive function holding the cells closely to the underlying connective tissue.

Figure 1-11 The development of exocrine and endocrine glands. A. Surface epithelial cells. B. Epithelial cells invading into the connective tissue. C. An epithelial connection is maintained in exocrine glands but is lost for endocrine glands (D).

Figure 1-12 Fibers and cells of loose connective tissue. Mast cells are usually found close to small blood vessels and have granules containing potent inflammatory mediators (e.g., histamine). Macrophages are phagocytic and plasma cells are the source of circulating antibodies (immunoglobulins). Pericytes are intimately associated with blood capillaries and venules, providing a potential source of new fibroblasts and smooth muscle cells. (From Cormack DH. Ham’s Histology. 9th edn.

Figure 1-14 Invagination of the serous membrane to form outer (parietal) and inner (visceral) layers (A). Development proceeded similar to a fist being pushed into a balloon (B and C). (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 200Q.)

Figure 1-15 Schematic transverse plane of the equine thorax. The thoracic portions of esophagus, aorta, caudal venae cavae, and the heart are shown in the mediastinal space.

Figure 1-16 Schematic sagittal plane of the abdominal cavity showing the peritoneum and its connecting folds. (From Evans HE, deLahunta A. Guide to the Dissection of the Dog. 8th edn. St Louis, MO: Elsevier, 2017.) 1. Pararectal fossa. 2. Rectogenital pouch. 3. Vesicogenital pouch. 4. Pubovesical pouch.

Chapter 2

Figure 2-1 Structure of a cell membrane. The lipid bilayer is represented by a thin film of lipid that is two molecules thick. The protein channels (pores) may be composed of a single protein or a cluster of proteins. The channels may have specificity for certain substances, or they may be restrictive because of size. Virtually all water diffuses through the protein channels.

Figure 2-2 A postulated mechanism for facilitated diffusion. A. The transported molecule enters the protein channel and binds with the receptor at the binding site. B. Subsequent to binding, the protein channel undergoes a conformational change to open the channel on the opposite side and the transported molecule is released, causing return of the protein channel to its original conformation.

Figure 2-3 Osmosis. A. Before osmosis. Equal volumes of aqueous solutions (solutes represented by black circles and open circles) are placed in compartments that are separated by a membrane permeable to water but not to the solutes (semipermeable membrane).

Figure 2-4 Hypothetical example of the tone of solutions. A. Before osmosis. Two aqueous solutions (solutes represented by black circles and open circles) of equal osmotic pressure are separated by a membrane permeable to water and open circle solutes (selectively permeable membrane). B. During osmosis. Effective osmotic pressure is exerted only by black circle solutes, and water diffuses from compartment 2 to compartment 1. At equilibrium, an open circle solute has a new, lower concentration that is equal throughout compartments 1 and 2. (Dashed lines represent divisions of equal volume.)

Figure 2-5 Effect of the tone of a solution on erythrocytes (red blood cells). A. The solution is hypotonic and the erythrocyte expands. B. The solution is isotonic and no change occurs in erythrocyte size. C. The solution is hypertonic and the erythrocyte decreases in size. The thick arrows indicate the direction of cell volume change. The thin arrows indicate the direction of water diffusion.

Figure 2-6 Pathways for the interconversion of grams, moles, osmoles, and equivalents. (From Reece WO. Physicochemical properties of solutions. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 2-7 Total body water and its distribution among the fluid compartments.

Figure 2-8 Schematic representation of the outer part of skin from a pig with special emphasis on the interstitial space, the space outside of the capillaries and cells. The fluid of the interstitial space is interstitial fluid (ISF). Hyaluronic acid of the amorphous ground substance gives ISF the characteristics of a gel. An abnormal increase of ISF in this location is evident in a condition known as edema.

Figure 3-1 The microhematocrit as it might appear for an anemic (A) and a normal (B) animal. The buffy coat, a narrow band of leukocytes above the erythrocyte mass, occupies an insignificant volume and is not accounted for. Accordingly, in the normal hematocrit, the plasma volume would be noted as 60%.

Figure 3-2 Cell types found in smears of normal peripheral blood: (A) polychromatophilic erythrocyte; (B) erythrocyte (mature); (C) platelets; (D) band neutrophil; (E) neutrophil (mature); (F) eosinophil; (G) basophil; (H) monocyte; (I) degenerating neutrophil; (J) large lymphocyte; (K) small lymphocyte. (From Cormack DH. Essential Histology. 2nd edn. Baltimore, MD: Lippincott Williams & Wilkins, 2001.)

Figure 3-3 Microscopically recognizable stages of erythroid and granulocytic maturation: (A) proerythroblast; (B) basophilic erythroblast; (C) polychromatophilic erythroblast; (D) normoblast; (E) polychromatophilic erythrocyte; (F) erythrocyte (mature); (G) myeloblast; (H),promyelocyte; (I) neutrophilic myelocyte; (J) neutrophilic metamyelocyte; (K) band neutrophil. (From Cormack DH. Essential Histology. 2nd edn. Baltimore, MD:,Lippincott Williams & Wilkins, 2001.)

Figure 3-4 Mechanisms by which neutrophils are attracted to sites of injury. A. Tissue injury and introduction of bacteria causes diffusion of a chemotactic substance to capillaries and venules. B. Chemotactic substance increases endothelial porosity and adhesion of neutrophils to endothelium. C. By a process known as diapedesis, the adhered neutrophils squeeze through endothelial pores. D. Neutrophils proceed to an injury site by amoeboid movement and phagocytize bacteria and other debris. WBC, white blood cell; RBC, red blood cell.

Figure 3-5 Mechanism by which sensitized cytotoxic T lymphocytes destroy a foreign cell. The attacked cell is killed by the release of cytotoxic and digestive enzymes from the T lymphocytes directly into the cytoplasm of the attacked cell. The T lymphocytes can proceed to other cells after their attack on a cell.

Figure 3-6 Antigen-antibody agglutination and precipitation. Antigens (molecules or cells) are grouped with other antigens by bivalent (two binding sites) antibodies. This causes them to agglutinate or precipitate. (Adapted from Hall JE. Guyton and Hall Textbook of Medical Physiology 12th edn. Philadelphia, PA: Saunders Elsevier, 2011).

Figure 3-7Schematic representation of one heme group and its associated polypeptide chain. Four of these combinations, at different orientations to each other, make up hemoglobin. The heme is held to its specific polypeptide chain (one of four in the protein globin) by cysteine (an amino acid) bridges and^ by bonding of the iron to imidazole groups of histidine (an amino acid). Molecular oxygen binds with iron. (Modified from Conn EE, Stumpf PK. Outlines of Biochemistry. New York: John Wiley & Sons, 1963.)

Figure 3-8 The stages of erythrocyte development.

Figure 3-9 Degradation of hemoglobin that began within mononuclear phagocytic system (MPS) cells. Iron released as shown is used preferentially for synthesis of new hemoglobin. Protein (globin) is degraded to amino acids and reutilized. Bilirubin released from MPS cells is insoluble and combines with a protein (known as free bilirubin) and is transported to the liver, where it is converted to bilirubin diglucuronide (soluble form of bilirubin). The soluble form enters the biliary system and is transported to the intestine. Bacterial reduction of bilirubin diglucuronide produces urobilinogen, which may be recirculated via the enterohepatic circulation or further reduced to urobilin or stercobilinogen. Some of the recirculated urobilinogen bypasses the liver, enters the general circulation, and is excreted in the urine. (From Reece WO, Swenson MJ. The composition and functions of blood. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 3-10 Summary of iron absorption, storage, and use. Iron must be in the ferrous (Fe²+) oxidation state to be transported across membranes. Intracellular iron is bound to or incorporated into various proteins or other chelates in its ferric (Fe³+) oxidation state to reduce its toxicity because free iron can catalyze free radicals from molecular oxygen and hydrogen ions and can have disastrous consequences for biological materials. Transported iron is bound to the protein apotransferrin and is known as transferrin. Iron is stored in tissues as either a diffuse, soluble, mobile fraction (ferritin) or as insoluble, aggregated deposits (hemosiderin). Principal locations of iron storage are the liver and spleen, followed by the kidney, heart, skeletal muscle, and brain. In the bone marrow, all erythroid forms have surface membrane receptors for transferrin. When internalized, released iron is transported into the mitochondria of developing erythrocytes, where it is incorporated into the heme molecule or it combines with the protein apoferritin to be stored as ferritin. (From Reece WO, Swenson MJ. The composition and functions of blood. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 3-11The five major stages in the formation and dissolution of a blood clot, or thrombus, around the site of vascular injury extending from the initiation of platelet activation after vascular damage through endothelial repair. (Adapted from Gentry PA. Blood coagulation and hemostasis. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 12th edn. Ithaca, NY: Cornell University Press, 2004. Used by permission of the publisher, Cornell University Press.)

Figure 3-12 Internal details of a platelet discernible at the electron microscope level. Dense bodies are also known as dense granules. (From Cormack DH. Essential Histology. 2nd edn. Baltimore, MD: Lippincott Williams & Wilkins, 2001.)

Figure 3-13 Platelet adhesion. This is the first response to blood vessel injury. The platelets lose their discoid shape and form sticky projections (pseudopods) for their continued adherence to the injured vessel and entrapment of other platelets.

Figure 3-14 Platelet cross-section showing how microtubular contraction results in extrusion of platelet granule contents into the open canalicular system and release from the platelet. (1) Clustering of granules into the center of the platelet after microtubular contraction; (2) contact of granule membrane with open canalicular system membrane; (3) fusion of granule membrane with open canalicular system membrane; (4) granule content extruded from open canalicular system. (Modified from MacIntyre DE. The platelet release reaction: association with adhesion and aggregation and comparison with secretory responses in other cells. In: Gordon JL, ed. Platelets in Biology and Pathology, Vol. 1. Amsterdam: Elsevier, 1976.)

Figure 3-15 The two pathways by which factor X activation can occur. In the extrinsic pathway (tissue factor pathway), activated factor X (FXa) is generated by the direct action of the tissue factor (TF)-factor VIIa complex, whereas in the intrinsic pathway (contact activation pathway), factor IXa must combine with factor VIII, phospholipids (PL), and calcium to form the tenase complex before factor X can be activated at a physiologically relevant rate. The final common steps in fibrin formation involve the formation of the prothrombinase complex, which activates prothrombin, allowing thrombin to convert fibrinogen to fibrin. (From Gentry PA. Blood coagulation and hemostasis. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 12th edn. Ithaca, NY: Cornell University Press, 2004. Used by permission of the publisher, Cornell University Press.)

Figure 3-16 The contact phase for the activation of factor IX, initiated when factor XII is activated by contact with damaged endothelium. Factor XIIa activates factor XI (accelerated by prekallikrein [PK] and high-molecular-weight kininogen [HK]). Activated factor XI, in the presence of Ca²+, activates factor IX (FIXa). FIXa, in association with other components of the tenase complex, allows for the activation of factor X and FXa’s association with the prothrombinase complex. PL, phospholipid.

Figure 3-17 The degradation of fibrin (fibrinolysis).

Figure 3-18Reversible equilibrium among the tissue proteins, plasma proteins, and plasma amino acids. (From Reece WO, Swenson MJ. The composition and functions of blood. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th Eedn. Ames, IA: Wiley- Blackwell, 2015.)

Chapter 4

Figure 4-1The neuron. Arrows indicate the direction of impulse conduction. In this myelinated nerve fiber in a peripheral nerve are shown the neurilemma (sheath of Schwann), axolemma (plasma membrane of axon), and nodes of Ranvier. The terminal branches are also referred to as the telodendritic zone. The axon is shown as discontinuous to allow for variable length.

Figure 4-2 The synapse. The enlargements progress in the direction of the arrows.

Figure 4-3 Illustration of an oligodendrocyte providing myelin internodes to three axons. A bisected view of a node, adjacent paranode regions, and part of an internode is shown in the foreground. The axon (A) bulges at the node and is exposed to extracellular space (ES). Loop profiles containing cytoplasm (Cyt) contact the axon at the paranodal regions. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 4-4 Schematic illustration of nodal and paranodal regions of myelinated fibers from the central nervous system (CNS) (left) and the peripheral nervous system (PNS) (right). In the CNS, myelin is formed by oligodentrocytes and nodes are broadly exposed to the extracellular space. In the PNS, outer cytoplasmic processes of adjacent neurolemmocytes (Schwann cells) overlap to restrict exposure to the extracellular space. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 4-5 Subdivisions of the brain according to the major divisions, being the cerebrum, cerebellum, and brain stem.

Figure 4-6 Subdivisions of the brain according to its development from the primary embryonic vesicles, the prosencephalon, mesencephalon, and rhombencephalon.

Figure 4-7 Relative locations of brain subdivisions to each other. BN, basal nuclei; E, epithalamus; T, thalamus; H, hypothalamus; P, pituitary gland; M, midbrain; CER, cerebellum. Dotted line for boundaries of basal nuclei represents its location on the midline.

Figure 4-8 Gross subdivisions of the brain of the dog. (From Beitz AJ, Fletcher TF. The brain. In: Evans HE, ed. Miller’s Anatomy of the Dog. 3rd edn. Philadelphia, PA: WB Saunders Company, 1993.)

Figure 4-9 Sources of input to the cerebellum of the dog. A. Exteroceptors in foot pads (pressure) and proprioceptors in joints, muscles, and tendons (tension). B. Vestibular apparatus (equilibrium) of the inner ear. C. Visual cortex of the cerebrum. D. Cerebral motor cortex (simultaneous impulse to muscle).

Figure 4-10 Structure of the spinal cord of the dog, showing a spinal cord segment. (Redrawn from Breazile JE. Textbook of Veterinary Physiology. Philadelphia, PA: Lea & Febiger, 1971.)

Figure 4-11 Transverse section of the spinal cord of the dog. Located within the gray matter are: (1) nerve cell bodies for sensory neurons in dorsal horns; (2) somatic motor neurons in ventral horns; and (3) autonomic motor neurons in lateral masses of ventral horns.

Figure 4-12 Caudal extremity of the spinal cord showing the cauda equina. Vertebrae numbers are designated on the right and the spinal cord segments are identified within the drawing of the cord. T = thoracic, L = lumbar, S = sacral, Co = coccygeal. (From Fletcher TF, Kitchell RL. Anatomical studies on the spinal cord segments of the dog. Am J Vet Res. 1966; 27: 1762.)

Figure 4-13 A schematic representation of the association of spinal nerves with vertebrae in the dog. Only the right half of the spinal cord, vertebrae, and spinal nerve pair is shown. A. C1 to C3 vertebrae. B. C7, T1, and T2 vertebrae. C. T12, T13, and L1 vertebrae. Although not consistently shown, the dorsal root ganglions are medial to the emergence of spinal nerves through intervertebral foramina.

Figure 4-14A spinal nerve and its location relative to its branches, roots, spinal cord, and vertebra.

Figure 4-15 Brachial plexus of the horse. It is formed by the contributions of the last three cervical and first two thoracic spinal nerves to supply the forelimbs. C, cervical; T, thoracic. The corresponding numbers refer to their respective spinal nerve.

Figure 4-16Origin and major distribution of cranial nerves in the dog. N, nerve; OPHTH, ophthalmic nerve; MAX, maxillary nerve; MAN, mandibular nerve. Acoustic nerve (VIII) now called vestibulocochlear nerve and spinal accessory nerve (XI) now called accessory nerve. (From Hoerlein BF, Oliver JE, Mayhew JG. Neurologic examination and the diagnostic plan. In: Oliver JE, Mayhew IG, eds. Veterinary Neurology. Philadelphia, PA: WB Saunders Company, 1987.)

Figure 4-17Diagrammatic representation of the efferent autonomic nervous system of the dog. Only one chain of the bilateral sympathetic trunk is shown. The lines showing sympathetic outflow (thoracolumbar) are red; lines for parasympathetic outflow (craniosacral) are blue. Numbers indicate sympathetic ganglia: (1) cranial cervical; (2) middle cervical; (3) cervicothoracic; (4) celiac; (5) cranial mesenteric; (6) caudal mesenteric. LU, lung; H, heart; LI, liver; S, stomach; SI, small intestine; SP, spleen; K, kidney; C, colon; B, urinary bladder; G, genitalia; T1, 1st thoracic vertebra.

Figure 4-18 The neurotransmitters acetylcholine (ACh) and norepinephrine (noradrenaline) associated with the autonomic nervous system of mammals.

Figure 4-19Establishment of a resting membrane potential by active transport of three Na⁺ outward coupled with the transport of two K⁺ inward. The uneven distribution results in the electronegativity within the fiber. The large concentration gradients for sodium and potassium across the resting nerve membrane are caused by the sodium-potassium pump (Na/K ATPase pump). ATP, adenosine triphosphate; ADP, adenosine diphosphate; Pi, inorganic phosphate.

Figure 4-20 Recording of a transmembrane potential during depolarization and repolarization of a nerve fiber microregion. A. The various phases of the action potential. B. The relative membrane permeability relationships between sodium and potassium ions associated with each of the phases (e.g., PN_a >> Pk refers to permeability for Na being greater than permeability for K, where > = greater, >> = much greater, and >>> greatest). V_m, transmembrane voltage; Py_a, membrane permeability to sodium; Pk, membrane permeability to potassium. (From Klein BG. Membrane potentials: the generation and conduction of electrical signals in neurons. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 12th edn. Ithaca, NY: Cornell University Press, 2004, 42. Used by permission of the publisher, Cornell University Press.)

Figure 4-21Current paths during the propagation of the action potential in myelinated (A) and nonmyelinated (B) axons. In both axons, the top portion of the membrane illustrates the distribution of the voltage-gated Na⁺ and K⁺ channels. The bottom portion of the axon shows the reversal of membrane polarity triggered by local depolarization. The local currents generated by an action potential flow to adjacent areas of the axonal membrane to depolarize and generate further action potentials. Myelinated axons have Na⁺ and K⁺ channels at the node of Ranvier and action potentials jump from one node of Ranvier to the next. This process is referred to as saltatory conduction. (From Uemura EE. Electrochemical basis of neuronal function. In Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Wiley-Blackwell, Ames IA, 2015.)

Figure 4-22Lower motor neuron going to striated muscle. This represents the final common pathway. To fire, a greater amount of excitatory (E) neurotransmitter must be released than inhibitory (I) neurotransmitter. Dashed lines represent axons of upper motor neurons.

Figure 4-23Examples of neuron placement within the central nervous system of mammals. A. Converging circuit. B. Diverging circuit. C. Reverberating circuit. D. Parallel circuit.

Figure 4-24 A neuron circuit from periphery to cerebral cortex. A minimum of three neurons is required: (1) afferent neuron in a mixed spinal nerve; (2) neuron ascending in a spinal cord tract to the thalamus; (3) final neuron in the circuit that transmits the impulse to the cerebral cortex.

Figure 4-25 The stretch reflex. Stretch of muscle stimulates the muscle spindle. The impulse travels to the spinal cord by way of an afferent neuron. Transmission of the impulse to an efferent neuron may be direct or by way of an interneuron as shown. Stimulation of an efferent neuron to striated muscle counteracts stretch by causing contraction. Muscle spindles, in addition to being involved in reflexes, also provide sensory input to cerebral and cortical levels as well as playing a role in voluntary control of muscular activity.

Figure 4-26 Cerebral meninges and arachnoid villi. The meninges consist of the dura mater (thickness exaggerated to illustrate dura mater sinus), arachnoid (darkened line), and pia mater. The subarachnoid space (exaggerated as shown) contains cerebrospinal fluid. The arachnoid villi project into the dura mater sinus (blood sinus) and provide an outlet for cerebrospinal fluid.

Figure 4-27 The perivascular space. The space is lined by pia mater that follows blood vessels into the brain substance. The space is filled with cerebrospinal fluid and communicates with the subarachnoid space. It extends only to the level of the capillaries and serves a lymphatic function.

Figure 4-28 The meninges of the spinal cord. Only half of the vertebra is shown to indicate the extension of the dura mater on to the spinal nerves. Note the presence of an epidural space.

Figure 4-29 The canine brain ventricles. A. Dorsal view of ventricles without brain substance. B. Lateral view of ventricles, which shows their location within the brain. C. Lateral view of ventricles without brain substance. (From Evans HE, de Lahunta A. A Guide to the Dissection of the Dog. 8th edn. Ames, IA: Wiley-Blackwell, 2017.)

Figure 4.30 Pathway of cerebrospinal fluid flow from choroid plexuses to the arachnoid villi that protrude into the dural sinuses. The interventricular foramina are openings from each of the two lateral ventricles (one in each cerebral hemisphere). The choroid plexuses produce the cerebrospinal fluid (stippled). The two foramina of Luschka (one shown) provide an exit from the sites of formation to the subarachnoid space of the brain and spinal cord. Note that cerebrospinal fluid circulates around the spinal cord. Cerebrospinal fluid circulates caudally through the central canal of the spinal cord as a continuation of the fourth ventricle. The central canal may not be patent all the way to caudal levels.

Chapter 5

Figure 5-1 Schematic drawings of five sensory receptors. A. Free nerve endings branch among the cells of the epidermis. B. Golgi tendon organs (a neurotendinous spindle) splay among the collagen bundles of a tendon and are activated by tension. C. Merkel’s corpuscle that ends in epidermis are pressure-sensitive touch receptors. D. Meissner’s corpuscle in dermis. These are highly sensitive for light touch. E. Pacinian corpuscle in dermis are extremely sensitive to transitory pressure such as vibratory stimuli. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 5-2 The sensory pain pathway. A cutaneous pain afferent fiber (A) and a visceral pain afferent fiber (B) converge on a common neuron (C). Neuron (D) conveys the pain impulse from the thalamus to the cerebral cortex.

Figure 5-3 Taste buds associated with papillae on the dog tongue. A. Fungiform and filiform papillae are represented by the finer dots. Circumvallate and conical papillae are located at the base. B. A vallate papillus with taste buds lining its moat-like furrow. Glands of von Ebner provide a watery secretion for dissolving substances to be tasted. C. A taste bud with its gustatory (taste) cells and supporting cells.

Figure 5-4 The olfactory region of the dog and the cells associated with smell. A. Nasal cavity. B. Olfactory epithelium from nasal cavity mucous membrane. C. Olfactory cells, basal cells, and sustentacular (supporting) cells are associated with olfactory epithelium. Subepithelial glands of Bowman (not shown) provide secretion-covering olfactory cilia.

Figure 5-5Transverse section through the dog head. The external ear (pinna and ear canal) provide for transfer of sound waves to the tympanic membrane. The ear canal in the dog has a vertical and an oblique component.

Figure 5-6 A schematic of the middle ear and inner ear that features the membranous labyrinth (black), which contains endolymph within its ducts, within the osseous labyrinth, which contains perilymph within the semicircular canals and vestibule. The vestibular aqueduct communicates with the subarachnoid space and its cerebrospinal fluid. (Adapted from Getty R, Foust HL, Presley ET, Miller ME. Macroscopic anatomy of the ear of the dog. Am J Vet Res, 1956; 17: 366.)

Figure 5-7Inside view of the middle ear. The malleus is attached to the tympanic membrane and the stapes is attached to the vestibular (oval) window. Muscle spindles in the tensor tympani and stapedius muscles initiate the stretch reflex in response to loud noises. Contraction of these muscles, respectively, tenses the tympanic membrane, limiting its movement, and reduces movement of the stapes.

Figure 5-8 Right inner ear (viewed from above showing its orientation with the skull).

(Adapted from Getty R, Foust HL, Presley ET, Miller ME. Macroscopic anatomy of the ear of the dog. Am J Vet Res. 1956; 17: 369.)

Figure 5-9 Drawing of a latex cast of the inner ear of the dog, occupying the osseous labyrinth. The membranous labyrinth would occupy the space filled by the latex cast. (Adapted from Getty R, Foust HL, Presley ET, Miller ME. Macroscopic anatomy of the ear of the dog. Am J Vet Res. 1956; 17: 370.)

Figure 5-10Membranous labyrinth. Hatched regions indicate the sites of neuroepithelium, including the spiral organ of the cochlear duct, the maculae of the utriculus (utricle) and sacculus (saccule), and the crista ampullares of the semicircular ducts. (From Banks WJ. Applied Veterinary Histology. 2nd edn. Baltimore, MD: Lippincott Williams & Wilkins, 1986.)

Figure 5-11 A. General structure of the ampullary crista in a semicircular duct. B. Ampullary hair cells responding to deflection of the cupula. (From Cormack DH. Ham’s Histology. 9th edn. Philadelphia, PA: JB Lippincott Company, 1987.)

Figure 5-12 A. General structure of the utricular and saccular maculae. B. Macular hair cells respond to movement of otolithic membranes. (From Cormack DH. Ham’s Histology. 9th edn. Philadelphia, PA: JB Lippincott Company, 1987.)

Figure 5-13 The cochlear portion of the inner ear. A. Cross-section through the cochlea, illustrating its coiled nature. B. Schematic representation of a section through one of the turns of the cochlea. C. Details of an organ of Corti.

Figure 5-14 Transmission of pressure waves in the cochlea. When the movement of the stapes is slow, pressure waves are transmitted through the perilymph with no movement of the basilar membrane. With greater movement of the stapes (higher frequency), pressure waves are directed through the endolymph with movement of the basilar membrane, and hence sound is perceived. High- and low-frequency sounds are related to regions of the basilar membrane where different sound wave frequencies can cause displacement. (Adapted from Spence AP, Mason EB. Human Anatomy and Physiology. 4th edn. St Paul, MN: West. Publishing Co., 1992.)

Figure 5-15 A. Schematic representation of the pathway of sound waves that enter the ear. B. Hair cells in the organ of Corti respond to shearing stresses generated by independent pivoting of the tectorial and basilar membranes on separate axes. (From Cormack DH. Essential Histology. 2nd edn. Baltimore, MD:,Lippincott Williams & Wilkins, 2001.)

Figure 5-16The external eye. The medial canthus is on the nasal side. The nasolacrimal duct originates in the medial canthus. The limbus is the junction of the sclera with the iris.

Figure 5-17 Diagram of an eyeball showing its basic structure. The pupil is the opening between the central projection of the iris.

Figure 5-18 The histologic organization of the cornea (top, anterior surface; bottom, posterior surface).

Figure 5-19Schematic representation of the relationship in the dog of the ciliary processes with the ciliary body, the zonular fibers (lens ligaments), and the posterior chamber. The ciliary muscles are a part of the ciliary body and are attached to the zonular fibers. The meshwork represents a collection location for aqueous humor that drains to aqueous veins in the sclera. The ciliary muscles encircle the eyeball. When contracted, tension on the lens ligaments is reduced and the lens becomes more convex.

Figure 5-20 Formation of aqueous humor by ciliary processes and its anterior flow. Arrows in the vitreous body indicate flow by diffusion of aqueous humor through the vitreous body. Some absorption occurs from the vitreous into choroidal vessels.

Figure 5-21Schematic drawing of the iridocorneal angle region of a dog. This is the location for drainage of aqueous humor. (From Dellmann HD. Textbook of Veterinary Histology. 4th edn. Philadelphia, PA: Lea & Febiger, 1993.)

Figure 5-22A simplified version of the retina. The arrows indicate the direction of impulse transmission from rods and cones in the outer aspect to the ganglion cells in the inner aspect. Impulse transmission is opposite to the direction of light.

Figure 5-23Photographs of the fundi of seven animals as seen by ophthalmoscopy. The disk-shaped structures are optic disks shown as an optic nerve head. Pecten, as shown for birds, is responsible for nourishment of the inner eye and retina. (Photographs courtesy of Drs Rachel Allbaugh and Gil Ben-Shlomo, Lloyd Veterinary Medical Center, Ophthalmology Service, Iowa State University.)

Figure 5-24 Photochemistry of the visual cycle. Metarhodopsin II, called photoexcited rhodopsin, triggers highly amplified visual excitation. CNS, central nervous system.

Figure 5-25 Location of the tapetum relative to the retina. The tapetum is shown as a broad band of cell layers between the choroid and the retina. Melanin is absent from the pigmented epithelium of the retina (outer layer of the retina), where tapetum is present. There is a pigmented layer in the choroid to aid light absorption.

Figure 5-26 Field of vision of the cat. The large central binocular area results from the forward position of the eyes. (From Coulter DB, Schmidt GM. Special senses I: Vision. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 11th edn. Ithaca, NY: Cornell University Press, 1993. Used by permission of the publisher, Cornell University Press.)

Figure 5-27Field of vision of the horse. It is relatively large because of the horse’s more laterally placed eyes. Note the small binocular area. (From Coulter DB, Schmidt GM. Special senses I: Vision. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 11th edn. Ithaca, NY: Cornell University Press, 1993. Used by permission of the publisher, Cornell University Press.)

Figure 5-28Extrinsic muscles of the eye of the dog. (Adapted from Helper LC. Magrane’s Canine,Ophthalmology. 4th edn. Philadelphia, PA: Lea & Febiger, 1989.)

Figure 5-29 The lacrimal production and drainage system of the eye of the dog. The accessory lacrimal glands are not shown. (From Helper LC. Magrane’s Canine Ophthalmology. 4th edn. Philadelphia, PA: Lea & Febiger, 1989.)

Figure 5-30 Third eyelid in the dog. (From Evans HE, deLahunta A. A Guide to the Dissection of the Dog. 8th edn. St Louis, MO: Elsevier, 2017.)

Chapter 6

Figure 6-1Schematic representation of the pituitary gland and its hypophysioportal circulation. Hypothalamic releasing and inhibiting hormones (1) reach anterior pituitary cells by way of this circulation (left). Posterior pituitary hormones (2) enter capillaries of the posterior pituitary (right). Open arrows indicate direction of blood flow: arrowheads indicate direction of hormone transport toward axon terminals. (From Cormack DH. Essential Histology. 2nd edn. Baltimore, MD: Lippincott Williams & Wilkins, 2001.)

Figure 6-2 Thyroid gland (bovine).

Figure 6-3 Photomicrograph of thyroid follicles showing iodinated thyroglobulin stored within the colloid. Parafollicular cells (C cells that secrete calcitonin) are positioned beside follicles and usually occur as single cells (arrow). (From Goff JP. The Endocrine System. In Reece WO. ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 6-4 Structural formulas of the thyroid,hormones, thyroxine (T4) and 3,5,3'- triiodotyrosine (T3).

Figure 6-5 The canine adrenal glands (ventral view). Their blood supply and venous drainage is by way of branches from the phrenicoabdominal arteries and veins.

Figure 6-6 Diagrammatic representation of the adrenal gland. A. Cross-section of the adrenal gland showing the contrasting appearance of the cortex and medulla. B. Magnification of boxed-in area in A that shows the different cell types associated with the three zones of the cortex.

Figure 6-7 Structural formulas of the principal adrenocortical hormones.

Figure 6-8Structural formulas of catecholamine hormones. They are formed from the amino acid tyrosine and are derivatives of catechol. The abbreviation “dopa” is derived from the German name of this compound, dioxyphenylalanine.

Figure 6-9 Three major pathways of prostaglandin synthesis. The open arrow indicates the site of aspirin inhibition. Thromboxane A₂ is biochemically related to the prostaglandins and is formed from them as shown. Thromboxane A₂ promotes the platelet release reaction associated with blood coagulation. Therefore, aspirin retards blood coagulation.

Chapter 7

Figure 7-1 Skeleton of the horse. (Adapted from McCracken TO, Kainer RA, Spurgeon TL. Spurgeon’s Color Atlas of Large Animal Anatomy: The Essentials. Baltimore, MD: Lippincott Williams & Wilkins, 1999.)

Figure 7-2 Skeleton of the ox. (From McCracken TO, Kainer RA, Spurgeon TL. Spurgeon’s Color Atlas of Large Animal Anatomy: The Essentials. Baltimore, MD: Lippincott Williams & Wilkins, 1999.)

Figure 7-3 Skeleton of the chicken. (Adapted from McCracken TO, Kainer RA, Spurgeon TL. Spurgeon’s Color Atlas of Large Animal Anatomy: The Essentials. Baltimore, MD: Lippincott Williams & Wilkins, 1999.)

Figure 7-4General features of typical vertebrae. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2009.)

Figure 7-5 Intervertebral disk, which is composed of hyaline cartilage and fibrocartilage and serves,to interconnect the bodies of contiguous vertebrae. The soft gelatinous interior of the disk is the nucleus,pulposus. The fibrocartilagenous collar supports the periphery of the disk. A prolapsed disk occurs when the nucleus pulposus herniates through the annulus fibrosus. (From Uemura EE. Fundamentals of Canine Neuroanatomy and Neurophysiology. 1st edn. Ames, IA: Wiley-Blackwell, 2016.)

Figure 7-6 Scapula of the horse. A. Lateral view. B. Medial view. The supraspinatus and infraspinatus muscles occupy the respective fossas noted on the lateral surface. The suprascapular nerve that innervates these muscles is a branch of the brachial plexus and arises from the medial surface at the neck of the scapula. Nerve injury is a cause for atrophy (reduction in size and loss of function) of the associated muscles.

Figure 7-7Pelvis of the ox. Lateral view (left) and dorsal view (right). (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley- Blackwell, 2009.)

Figure 7-8 The pelvic bones of the cow (viewed from in front and somewhat below) through which the calf must pass at birth. The caudal aspect of the sacrum erroneously appears as an obstruction because of the view. The arrows indicate the greatest transverse and dorsoventral diameters of the pelvic girdle.

Figure 7-9 Comparison of anatomy of bones of the thoracic limb. A. Scapula. B. Scapulohumeral (shoulder) joint. C. Humerus. D. Elbow joint. E. Antebrachium (radius and ulna). F. Carpus. G. Metacarpus. H. Digit (phalanges). (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2009.)

Figure 7-10 Comparison of anatomy of bones of the pelvic limb. A. Pelvis. B. Coxofemoral (hip) joint. C. Femur. D. Patella. E. Stifle joint. F. Crus (tibia and fibula). G. Tarsus (hock). H. Metatarsus. I. Digit (phalanges). (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley- Blackwell, 2009.)

Figure 7-11Metacarpal and phalangeal bones of the thoracic limb of the horse. A. Right metacarpal bones (palmar view). The third (III) or large metacarpal bone (cannon bone) is fully developed; the second (II) and fourth (IV) are much reduced and are commonly called the small metacarpal or splint bones. B. The phalanges and distal part of right metacarpal bones (lateral view).

Figure 7-12The structure of a long bone. The endosteum and periosteum designations refer only to their locations and do not reflect their cellular nature and extent. Note the parallel arrangement of the trabeculae to form scaffolding for maximum strength in response to its assumed load.

Figure 7-13Three-dimensional diagram showing the appearance in cross section and longitudinal section of the components that enter into the structure of the cortex of the shaft of a long bone. (From Ham AW, Cormack DH. Histology. 8th edn. Philadelphia, PA: JB Lippincott Company, 1979.)

Figure 7-14 An osteon (Haversian system). A. Concentric lamellae, showing osteocytes within their lacunae and their communicating canaliculi. B. Cytoplasmic extensions of osteocytes into canaliculi for communication with other osteocytes.

Figure 7-15 The four zones of a cartilage (epiphyseal) plate.

Figure 7-16 The appearance presented by both longitudinal and cross sections of different areas of the epiphyseal plate and metaphysis at the periphery of a growing shaft. A. The blackened area is the location on the long bone for parts B and C. B. Horizontal lines extend to their respective cross sections. Brown areas are tunnels or openings to tunnels. The oblique lines represent cartilage and the stippled structures represent calcified matrix. C1. Chondrocytes in their lacunae in the zone of hypertrophy. C2. Tunnels formed in the zone of calcified matrix. Trabeculae are composed of both cartilage and bone. C3. Haversian system transforming tunnels into compact bone.

Figure 7-17 Bone growth by apposition. (Adapted from Ham AW. Histology. 1st edn. Philadelphia, PA: J.B. Lippincott, 1950.)

Figure 7-18 Sites of bone deposition and resorption in the process of lengthening and remodeling of long bones. Bone is shown in tan, cartilage in blue-green. (From Ham AW and Cormack DH. Histology. 8th edn. Philadelphia, PA: JB Lippincott Company, 1Q7Q.)

Figure 7-19 Osteoclastic activity that precedes bone remodeling. Osteoclasts advance a resorption cavity into the bone and are immediately followed by a vascular loop accompanied by precursor cells that multiply and differentiate into osteoblasts. Osteoblasts lay down new layers of osteoid. Canaliculi are formed and osteoblasts become osteocytes. Successive layers of new bone are deposited to give the concentric lamellar rings of Haversian bone. (From Whittick WG. Canine Orthopedics. 2nd edn. Philadelphia, PA: Lea & Febiger, 1QQ0.)

Figure 7-20 Bone fracture repair. A. Fracture has been reduced and immobilized. Repair involves the appearance of a palpable callus. A cartilaginous callus precedes the mineralized callus. B. Fracture completely healed. The bone has been remodeled to conform to lines of stress. The eriginal fracture site is obliterated. (From Whittick WG. Canine orthopedics. 2nd Edn. Philadelphia, PA: Lea & Febiger, 1QQ0.)

Figure 7-21 Articular cartilage covers the opposing bony surfaces of a synovial joint as shown in this diagram of a stifle. The joint space is filled with synovial fluid from the synovial membrane of the surrounding joint capsule. A meniscus composed of fibrocartilage extends into the joint cavity. (From Dellmann HD and Eurell JA, eds. Textbook of Veterinary Histology. 5th edn. Baltimore, MD: Williams & Wilkins, 1Qq8.)

Figure 7-22 Blood and nerve supply of a synovial joint. An artery is shown supplying the epiphysis, joint capsule, and synovial membrane. Note the arteriovenous anastomosis. The articular nerve contains the following: (1) sensory fibers (mostly pain) from the capsule and synovial membrane, (2) autonomic fibers (postganglionic, sympathetic to blood vessels), (3) sensory fibers (pain, and others with unknown functions) from the adventitia of blood vessels, and (4) proprioceptive fibers from Ruffini endings and from small lamellated corpuscles (not shown). Arrows indicate the direction of conduction. (From Gardner E, Gray DJ, O’Rahilley R. Anatomy. 4th edn. Philadelphia, PA: WB Saunders, 1975.)

Chapter 8

Figure 8-1 Smooth muscle cells exposed in their longitudinal and cross-sectional planes. The cells are characteristically spindle-shaped and have a centrally located nucleus.

Figure 8-2 Cardiac muscle cells exposed in their longitudinal and cross-sectional planes. Note elongated, branching cells with irregular contours at their junctions with other cells, the intercalated disk. Intercalated disks indicate the positions of apposed borders of contiguous muscle cells. Most cells have a single nucleus, some contain two. The nucleus occupies a central position in the muscle cell.

Figure 8-3 Photomicrograph of skeletal muscle showing red fibers (R) and white fibers (W). Red fibers have more mitochondria (M) packed between their myofibrils, especially in association with capillaries (cap). (From Ham AW, Cormack DC. Histology. 8th edn. Philadelphia, PA: JB Lippincott, 1Q7Q.)

Figure 8-4 Photomicrograph of a longitudinal section of skeletal muscle fibers. Note the striations and the multiple, peripherally located nuclei.

Figure 8-5 Longitudinal section of a muscle. The connective tissue elements of muscle are continuous with a tendon. (Adapted from Ham AW. Histology. 7th edn. Philadelphia, PA: JB Lippincott, 1974.)

Figure 8-6The division of muscles into smaller parts, down to myofibrils. (From Feduccia A, McCrady E. Torrey’s Morphogenesis of the Vertebrates. 5th edn. New York: John Wiley & Sons, 1991.)

Figure 8-7 The division of myofibrils into sarcomeres. A. Cross-section of a muscle fiber. B. Longitudinal arrangement of myofilaments within sarcomeres. C. Spatial arrangement of the myofilaments within a sarcomere. D. Further details of the relationship between actin and myosin molecules.

Figure 8-8 Photomicrograph of a longitudinal section of a skeletal muscle myofibril, showing the characteristic banding. The thick dark vertical stripes are A bands of myofibrils; the light stripes contain the I bands centered by Z lines. The H zone, a paler region, is seen in the center of each A band. The pale fine lines running horizontally through the dark A bands are narrow regions of sarcoplasm lying between individual myofibrils. (From Ham AW. Histology. 7th ed. Philadelphia, PA: JB Lippincott, 1974.)

Figure 8-9Cross-section of part of a mammalian skeletal muscle fiber, showing the sarcoplasmic reticulum that surrounds myofibrils. Two transverse (T) tubules supply a sarcomere and are in close association with the sarcoplasmic reticulum. The T tubules open to the surface of the sarcolemma and contain extracellular fluid. (From Ham AW, Cormack DC. Histology. 8th edn. Philadelphia, PA: JB Lippincott, 1979.)

Figure 8-10 Sarcoplasmic reticulum in the extracellular spaces between the myofibrils, showing a longitudinal system paralleling the myofibrils. Also shown in cross-section are T tubules (arrows) that lead to the exterior of the fiber membrane and are important for conducting the electrical signal into the center of the muscle fiber. (From Fawcett DW: The Cell. Philadelphia, PA: WB Saunders, 1981.)

Figure 8-11Schematic of the neuromuscular junction and the associated acetylcholine receptor channel. The terminal branch of the axon is separated from the muscle fiber by a gap known as the synaptic cleft. A neurotransmitter, acetylcholine (Ach) is stored in the membrane-bound synaptic vesicles. (From Bailey JG. Muscle physiology. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals, 12th edn. Ithaca, NY: Cornell University Press, 2004. Used with permission of the publisher, Cornell University Press.)

Figure 8-12Drawing of three motor end plates synapsing on skeletal muscle fibers. Each of three terminal branches of an axon ends in a perfusion of short branches collectively designated an end plate. The bottom end plate is viewed from its edge. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 8-13The components of the actin and myosin myofilaments associated with contraction of the sarcomere. Arrows indicate the direction of actin movement during contraction (shortening of myofibrils).

Figure 8-14 Conformational changes of the actin filament after calcium binding. A. The actin filament with its three proteins, actin, troponin, and tropomyosin. The vertical line indicates the cross-section location for B and C. B. The active sites on actin are covered by tropomyosin. C. Ca²+ binds to troponin, resulting in a conformational change that exposes the active sites on actin. Myosin cross-bridge heads attach to actin active sites and myofibril contraction begins.

Figure 8-15 A cycle of contraction followed by relaxation. A. The dashed line indicates transfer of depolarization from the sarcolemma and T tubules to the sarcoplasmic reticulum. Depolarization is followed by Ca²+ release from the sarcoplasmic reticulum with diffusion to the myofibrils. Ca²+ binds to troponin, removing the blocking action of tropomyosin. Myosin cross-bridge heads attach to active sites on actin and bend toward the center of the myosin molecule. B. Relaxation begins when ATP binds to cross-bridge heads, causing their detachment from actin. Ca²+ is returned to the sarcoplasmic reticulum using energy supplied by ATP. Removal of Ca²+ from troponin restores the blocking action of tropomyosin.

Figure 8-16 Energy changes associated with actin and myosin interaction that result in muscle shortening. See text for details. ATP, adenosine triphosphate; ADP, adenosine diphosphate; Pi, inorganic phosphorus.

Figure 8-17 Increasing muscle strength by increasing the frequency of contraction. This is known as wave summation. Tetany occurs when individual contractions are fused and cannot be distinguished from each other. (From Carlson AJ, Johnson V. The Machinery of the Body. 4th edn. Chicago, IL: University of Chicago Press, 1953.)

Figure 8-18 The staircase phenomenon of skeletal muscle. This is also known as treppe. Successive stimuli of the same intensity produce contractions of increasing strength. (From Carlson AJ, Johnson V. The Machinery of the Body. 4th edn. Chicago, IL: University of Chicago Press, 1953.)

Figure 8-19 Contraction of smooth muscle. A. Physical structure of smooth muscle. Dense bodies attach either to the cell membrane or to an intracellular structural protein that links several dense bodies together. The dense bodies are functionally similar to Z lines. B. A translucent view of a relaxed smooth-muscle cell. C. A translucent view of a contracted smooth-muscle cell. Dense bodies and details of actin and myosin filaments not shown in B and C.

Chapter 9

Figure 9-1The canine heart and its major vessels in the thorax (left lateral view). 1, Flattened base;,2, apex; 3, right ventricle; 4, left ventricle; 5, right ventricular margin; 6, left ventricular margin. (From Adams DR. Canine Anatomy: A Systemic Study. Ames, IA: Iowa State Press, 2004.)

Figure 9-2 Cross-sectional schematic representation of a mammalian heart. A. Embryologic invagination of the heart into the pericardial coelom (becomes the pericardial sac). B.

Sagittal section of the heart with the pericardial sac. C. Details of the heart wall and pericardium.

Figure 9-3 Left view of the bovine thorax and abdomen showing location of the heart relative to the reticulum. Foreign objects (nails, wire), sometimes ingested by cattle, accumulate in the reticulum (one of the bovine forestomachs). Contraction of the reticulum can force pointed objects through the reticulum wall and the diaphragm, causing final penetration of the pericardium and subsequent inflammation (pericarditis).

Figure 9-4 Cross-sectional view of horse heart at the ventricular level showing the relative thickness of the myocardium and the orientation of the muscle fibers.

Figure 9-5 A sagittal section of the canine heart. The right and left chambers are shown with separation of the atria and ventricles by atrioventricular valves. The auricles are extensions of the atria. The aorta is seen to be arising from the left ventricle. The pulmonary trunk arises from the right ventricle (origin not visible) and divides into right and left pulmonary arteries beyond the pulmonary semilunar valve. The cranial vena cava and caudal vena cava (not visible) deliver venous blood (low oxygenated) into the right atrium.

Figure 9-6 Heart valves. A. Location relative to the chambers and the aorta. The pulmonary trunk and its semilunar valve are not shown. B. A view of the heart from above the ventricles with the atria removed (at the level of the straight line shown in A to show the semilunar and atrioventricular valves). The first branches from the aorta are the coronary arteries. The coronary sinus opens into the right atrium and receives blood from the heart wall through the coronary veins.

Figure 9-7Schematic of the blood pathway through the heart. Venous blood from the entire body (except for the lungs and some of the heart) enters the right atrium (1) and then flows sequentially through the right ventricle (2), pulmonary trunk (3), pulmonary arteries/capillary bed/pulmonary veins (4), left atrium (5), left ventricle (6), and ascending aorta (7), and into all of the body (except for the alveoli). (From Adams DR. Canine Anatomy: A Systemic Study. Ames, IA: Iowa State Press, 2004.)

Figure 9-8Schematic representation of the functional circulatory system. A network of arteries, arterioles, capillaries, venules, and veins exists between the aorta and cranial and caudal venae cavae.

Figure 9-9 Schematic drawing of the microvasculature. Capillaries arise from both an arteriole and a metarteriole; precapillary sphincters are present. The metarteriole continues into a central channel, followed by a postcapillary venule, and as the venules increase in diameter they are called pericytic venules in which pericytes form a continuous layer. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 9-10 Schematic representation of a cross-,section through the endothelial wall of a muscle (continuous) capillary. Portions of endothelial cells are shown; these are separated from each other by intercellular clefts. Pericytes are outside of endothelial cells and are enclosed by a common basement membrane. Many pinocytotic vesicles are also shown.

Figure 9-11 Valves of a vein showing the pumping action of adjacent muscles. External pressure on veins causes blood to advance in only one direction because backflow is prevented by venous valve closure.

Figure 9-12 Graphic illustration of decreasing pressures from major arteries to major veins. Note the sharp decrease in pressure in the arterioles and the more gentle slope in the much wider vascular bed made up of capillaries. (Drawing made from The Dukes Physiology Film Series (DKS-15), Ames, IA: Iowa State University, 1969.)

Figure 9-13 General scheme of mammalian circulation showing the pulmonary system, which serves the lungs, and the systemic system, which serves the remainder of the body. The pulmonary circulation is shown in black.

Figure 9-14Schematic representation of the lungs and the pulmonary circulation. The circled inset represents a functional unit of the lung, the alveolus. Mixed venous blood leaves the right ventricle through the pulmonary trunk and is oxygenated at the level of the alveoli. Oxygenated blood returns to the left atrium through the pulmonary veins.

Figure 9-15Cranial aspects of the systemic circulation (dog). The first branches of the aorta supply the heart muscles through the coronary arteries. The descending aorta is composed of the thoracic and abdominal aorta. The main arteries to the forelimbs arise from the left subclavian artery on the left side and from the brachiocephalic trunk on the right side. The carotid arteries ascend to the head.

Figure 9-16The mammalian hepatic portal system. Blood in the portal vein from the stomach, spleen, pancreas, and intestines goes to the liver, where it flows through the sinusoids and is reformed by the central vein of each lobule. It finally enters the caudal vena cava through the hepatic veins.

Figure 9-17Schematic representation of lymph drainage. Interstitial fluid gains access to the blind beginnings of lymph capillaries and proceeds centrally through lymph vessels of increasing size. Lymph nodes are located along the course of lymph vessels. Lymph is returned to blood by drainage into veins.

Figure 9-18 Special structure of the lymphatic capillaries that permits passage of high- molecular-weight substances into the lymph. The structures radiating from the capillaries are anchoring filaments that give support to portions of endothelial cells where the capillaries begin. The unsupported portion of the endothelium allows fluid to flow into the capillary (arrows), as shown in B and C. Raised pressure in the capillary closes the flap against the overlapping supported endothelium, as shown in A. (From Leak LV. The fine structure and function of the lymphatic vascular system. In: Meessen H, ed. Handbuch der Allgemeinen Pathologie. New York: Springer-Verlag, 1972.)

Figure 9-19Internal structure of a lymph node. Lymph enters through afferent lymphatics and leaves through efferent lymphatics. The lymph percolates through the coarse mesh, on which many fixed mononuclear phagocytic cells are located. Lymphocytes are produced in the primary nodules and accumulate throughout the fine mesh (dark tan). A fine mesh holds small lymphocytes better than a coarse mesh.

Figure 9-20 Projection of viscera on the left body wall of the female dog showing the location of the spleen relative to other body organs. The dog spleen is somewhat variable in position and its long axis can be almost longitudinal.

Figure 9-21Schematic representation of the pig spleen. Multiple branches of the splenic artery enter the capsule and extend into the trabeculae. The lymphatic nodules and periarterial sheaths compose the white pulp that produces lymphocytes. The red pulp is the reticular fiber mesh that acts as a filter because of its fixed macrophages. Smooth muscle cells are present in the capsule and in the trabeculae. The venous sinuses collect filtered blood and drain into venules and finally trabecular veins (not shown).

Figure 9-22Conduction system of the mammalian heart. Impulse originates in the S-A node located near the junction of the venae cavae with the right atrium. The internodal pathways conduct the impulse throughout the atria and the left- and right-bundle branches of Purkinje fibers conduct the impulse throughout the ventricles. The A-V node and bundle conduct the impulse from the atria to the ventricles.

Figure 9-23The cardiac cycle of the mammalian heart. As shown in the key for the cycle sequence, the single chambers represent both right and left atria and ventricles. The single semilunar valve represents both the pulmonary and aortic semilunar valves that separate the ventricles from their respective pulmonary trunk and aorta. The dotted lines surrounding the ventricles correspond to the would-be size related to expansion and contraction. 1, A-V valves open; 2, ventricles receive blood; 3, atria contract and empty; 4, ventricles begin contraction and close A-V valves; 5, atria relax and begin to fill; 6, ventricular pressure increases; 7, semilunar valves open; 8, blood ejection begins from ventricles through semilunar valves; 9, ventricles begin relaxation; and 10, semilunar valves close, while A-V valves are still closed.

Figure 9-24 Examples of different electrode placements (leads) and their characteristic wave forms for the dog. (From Breazile JE. Textbook of Veterinary Physiology. Philadelphia, PA: Lea & Febiger, 1971.)

Figure 9-25 Close-up of normal canine lead II P-QRS-T complex. Measurements for amplitude (in millivolts) are indicated by positive and negative movement; time intervals (in hundredths of a second) are indicated from left to right. There is much variation in T wave configuration, which is shown as negative in this illustration. Paper speed, 25 mm/ s; 1 cm = 1 mV. (Modified from Tilley LP. Essentials of Canine and Feline Electrocardiography. 3rd edn. Philadelphia, PA: Lea & Febiger, 1992.)

Figure 9-26 Simultaneous recording of electrocardiogram (lead II), phonocardiogram, respiration, and blood pressure of a dog. The correlation of events is represented by correlation line A (first heart sound, lub; ECG; blood pressure) and B (second heart sound, dub; blood pressure). For line A: immediately after depolarization of the ventricles, heart contraction begins, the first heart sound is perceptible, and blood pressure begins to increase. For line B: ventricular relaxation begins, blood pressure decrease begins, and semilunar valves close. Valve closure produces the second heart sound and causes a momentary blood pressure bounce upward (dicrotic notch). Respiratory sinus arrhythmia (an example of the Bainbridge reflex) is shown by correlating the inspiratory phase of the breathing cycle (blood flow to right atrium increases) with increased heart activity (R-R interval decreased). Paper speed, 25 mm/s; 1 cm = 1 mV. See Figure Q-25 for a study of the grid measurements.

Figure 9-27 The reflexes controlling blood pressure involve receptors in the aortic and carotid sinuses and centers in the medulla oblongata. To lower blood pressure the vasomotor center is inhibited, resulting in vasodilatation, and the cardioinhibitory center is stimulated, resulting in diminished heart activity.

Figure 9-28 Generation of systemic blood pressure during left ventricular systole and maintenance of blood flow and pressure during diastole. A. Contraction of ventricle and stretch of elastic aorta (arrowheads show direction of contraction and stretch). B. This is followed by retention of systemic blood in vessels by the closed aortic semilunar valve. Continued blood flow is provided by the elastic recoil of the aorta. Solid lines in A represent ventricular and aortic size at the end of systole. Solid lines in Brepresent ventricular and aortic size at the end of diastole. The stippling in the ventricle and aorta represents blood. The dotted lines indicate the would-be size before and after contraction and/or stretch.

Figure 9-29 Recording blood pressure from a surgically placed cannula and an electrocardiogram from lead II in an anesthetized dog. Note the increase in pressure that follows the QRS waves (depolarization of ventricles and subsequent contraction). Pulse pressure is represented by the double arrow between diastolic and systolic blood pressure.

Figure 9-30 Diversion of blood flow according to need. Greater blood flow to kidneys and intestine at rest (A) and to muscles during exertion (B). Cardiac output (CO) is greater during exertion. Blackened vessels indicate locations of greater blood flow.

Figure 9-31Cross-section of equine thorax at a level that shows the esophagus, caudal vena cava, aorta, and heart within the mediastinal space. Expansion of thoracic volume occurs with inspiration, which leads to lowering of pressure in the mediastinal space. This is followed by expansion of volume (and lowering of pressure) in thin-walled structures (e.g., lymphatics, venae cavae, esophagus) within the mediastinal space.

Figure 9-32Laboratory model of the thorax. This illustrates the mechanics of breathing and the influence of breathing on venous blood return to the heart. Structures: 1, thorax; 2, lung; 3, vena cava; 4, diaphragm; 5, venous blood reservoir. Pressures: a, intrapulmonic; b, intrapleural; c, intravenous. During inspiration, the diaphragm (4) contracts (downward pull of glove), resulting in an increase in thoracic volume (1) and a decrease in intrapleural pressure (b). This is followed by an increase in lung volume (2) and a decrease in intrapulmonic pressure (a). Air flows into the lung. Also, there is an increase in vena cava volume (3), simultaneous with lung volume increase, and a decrease of its intravenous pressure (c). Blood flow (5) to the heart increases because of intravenous pressure decrease. During expiration the diaphragm (4) relaxes, resulting in a decrease in the volumes of the thorax (1), lung (2), and vena cava (3), and an increase in intrapleural (a), intravenous (b), and intrapulmonic (c) pressures. Air flows out of the lung. Valves in veins prevent blood from flowing backward.

Figure 9-33A schematic representation of a capillary bed. Blood is supplied to capillaries by arterioles and leaves the capillaries through the venules. Tissue cells are surrounded by interstitial fluid (ISF). Water and dissolved substances from blood capillaries are interchanged with ISF, intracellular fluid, and lymph capillaries by diffusion. ISF not returned to the blood capillaries is returned as lymph through lymphatic capillaries. Small arrowheads represent the direction of blood flow; large arrowheads represent the direction of diffusion.

Figure 9-34 Physical factors associated with filtration at the arterial end and reabsorption at the venous end of a capillary. Values are in millimeters of mercury (mm Hg). P_c, capillary hydrostatic pressure; π_c, plasma colloidal osmotic pressure; Pif, interstitial fluid hydrostatic pressure; π_if, interstitial fluid colloidal osmotic pressure. Open arrows indicate the direction of influence of P_ci. π_ci. Pif, and π_if.

Chapter 10

Figure 10-1 The nostrils of several domestic animals. A. Horse. B. Cow. C. Sheep. D. Pig. E. Dog. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2009.)

Figure 10-2 Transverse section of the head of a horse showing the division of the nasal cavities. The airways are noted as the dorsal, middle, ventral, and common meatus. The conchae consist of turbinate bones covered by a highly vascularized mucous membrane. It can be seen that incoming air is exposed to a large surface area for adjustment of its temperature and humidity.

Figure 10-3 Midsagittal section of the head of a cow with the nasal septum removed. The stippled area represents the pathway for air through the nasal cavity, pharynx, larynx, and trachea. The glottis is the opening to the larynx that is continued caudally by the trachea.

Figure 10-4 Cranial view of canine glottis (opening to the larynx, between the vocal cords) and epiglottis (cranial extension from the larynx). The soft palate is not shown in the location that would be seen with usual mouth opening techniques.

Figure 10-5Schematic view of an endotracheal tube in place relative to the structures encountered.

Figure 10-6 Schematic representation of a cross-section of trachea. A. Pseudostratified epithelium lines the lumen. B. Glands in the lamina propria. C. Glands in the submucosa. D. Cartilage. E. Band of smooth muscle. The tracheal muscle and the cartilage form most of the tracheal wall. (From Eurell JA, Frappier BL. Dellmann’s Textbook of Veterinary Histology. 6th edn. Ames, IA: Blackwell Publishing, 2006.)

Figure 10-7Schematic representation of lung subdivisions. (From Mackenna BR, Callander R. Illustrated Physiology. 6th edn. Edinburgh: Churchill Livingstone, 1QQ7.)

Figure 10-8 Electron micrograph of a mouse lung showing an attenuated portion of alveolar epithelium and its proximity to capillary endothelium. The respiratory membrane (without alveolar fluid layer) is composed of the following: A. alveolar epithelium, B. alveolar epithelial basement membrane, C. interstitial space, D. capillary endothelial basement membrane, and E. capillary endothelium. (From Reece WO. Respiration in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 10-9 Radiographs of healthy canine thorax. A. Dorsal-ventral view. Radiographs of healthy canine thorax. B. Lateral view. The heart and major blood vessels are visible because blood is relatively radiopaque. Blood in lesser blood vessels gives a slightly cloudy appearance to the lung field as compared with the clear appearance of air in the trachea. (Radiographs courtesy of Dr Elizabeth Riedesel, Lloyd Veterinary Medical Center, Radiology Section, Iowa State University.)

Figure 10-10Schematic transverse section of equine thorax showing the relationships of the visceral, costal, and mediastinal pleura. The aorta, esophagus, venae cavae, and thoracic lymph duct (not shown) are within the mediastinal space. The esophagus, venae cavae, and lymph duct (soft structures) respond by increasing and decreasing pressures within their lumens, associated with similar changes in intrapleural and mediastinal spaces.

Figure 10-11 Schematic of the thorax during inspiration (ventral view). Shown are the directions of enlargement (arrows) when the diaphragm and inspiratory intercostal muscles contract during inspiration.

Figure 10-12 Subdivisions of lung volume. The values shown for lung volume are those that approximate values for an average adult human male. (From Guyton AC, Hall JE. Textbook of Medical Physiology. 11th edn. Philadelphia, PA: Elsevier Saunders, 2006.)

Figure 10-13 Intrapleural and intrapulmonic (intrapulmonary) pressures associated with inspiration and expiration. (Adapted from Ganong WF. Review of Medical Physiology. 20th edn. New York: McGraw-Hill, 2001.)

Figure 10-14 Pneumothorax (ventral view). The volume of air that enters at the unnatural opening exceeds that which enters the trachea when the intrapleural volume is increased during inspiration. The intrapleural pressure reduction is then not sufficient to permit lung inflation. The dark arrows show the directions of thoracic enlargement when the diaphragm and inspiratory intercostal muscles contract during inspiration.

Figure 10-15 Direction of diffusion for oxygen (O₂) and carbon dioxide (CO₂), as shown by arrows in progression from the alveoli to the arterial end pulmonary capillaries, arterial end tissue capillaries, tissue cells, venous end tissue capillaries, venous end pulmonary capillaries, and back to the alveoli. Gas flow as follows: in the pulmonary alveolus the PCO₂ is 40 mm Hg and the PO₂ is 104 mm Hg; at the arterial end of the pulmonary capillary the PO₂ is 100 mm Hg and the PCO₂ is 40 mm Hg; at the arterial end of the tissue capillary the PO₂ is 100 mm Hg and the PCO₂ is 40 mm Hg; in the tissue cell the PCO₂ is 50 mm Hg and the PO₂ is 11

Figure 11-1 Side view of female dog showing general location of kidneys, ureters, urinary bladder, urethra, urethral orifice, and vagina.

Figure 11-2 Ventral view of canine kidneys showing renal arteries, veins, and ureters and their positions relative to the aorta, vena cava, and adrenal glands.

Figure 11-3 Right kidney from various species. A. Horse. B. Cattle. C. Sheep. These represent heart-shaped, lobulated, and bean-shaped kidneys, respectively. (1) Renal artery; (2) renal vein; (3) ureter.

Figure 11-4 Midsagittal plane of horse kidney showing cortex, medulla, renal pelvis, hilus, ureter, renal artery, and renal vein.

Figure 11-5 Ureterovesicular junction (oblique entrance of ureter into the urinary bladder). A. Urine is conveyed to the urinary bladder from the renal pelvis by peristalsis and enters at the ureterovesicular junction. B). During micturition (emptying of the urinary bladder), urine is directed through the neck of the bladder to the urethra. Urine does not reenter the ureter because the ureterovesicular junction is closed by the hydrostatic pressure of urine associated with contraction of the detrusor muscle of the bladder wall.

Figure 11-6 Midsagittal plane of the mare pelvis showing positions of the urinary bladder and urethra relative to other organs.

Figure 11-7 Types of mammalian nephrons. A. Juxtamedullary (long-looped) nephron. B. Cortical nephron.

Figure 11-8 A. Component parts of a juxtamedullary nephron (mammalian) relative to their locations in the cortex and medulla. B. Midsagittal section of the kidney showing the location of a juxtamedullary nephron (exaggerated size) relative to the cortex, medulla, and renal pelvis.

Figure 11-9 The functional nephron with blood supply. A juxtamedullary nephron is shown so as to display the vasa recta. (1) Bowman’s capsule; (2) proximal tubule; (3) descending limb of loop of Henle; (4) thin ascending limb of the loop of Henle; (5) thick ascending limb of the loop of Henle; (6) distal tubule; (7) connecting tubule; (8) cortical collecting tubule; (9) outer medullary collecting duct; (10) inner medullary collecting duct; (11) afferent arteriole; (12) glomerulus; (13) efferent arteriole; (14) peritubular capillaries; (15) vasa recta; (16) to renal vein. The thick ascending limb of the loop of Henle becomes a distal tubule when it passes between the afferent and efferent arteriols at the glomerulus (location of the macula densa).

Figure 11-10 Summary of kidney blood flow and tubular fluid flow as it applies to the nephron. After removal of the filtration fraction of plasma at the glomerulus, the remaining blood that enters the efferent arteriole is distributed via peritubular capillaries to the nephron, as shown. The fraction of plasma filtered at the glomerulus enters Bowman’s capsule as a glomerular filtrate. It continues through the nephron tubules and ducts as tubular fluid. The tubular fluid is subjected to reabsorption and secretion and enters the renal pelvis as urine. Urine is finally evacuated from the urinary bladder by micturition.

Figure 11-11The juxtaglomerular (JG) apparatus. The JG apparatus is located at the junction of the distal tubule and its glomerulus of origin. It is associated with regulation of blood flow and filtration fraction for the nephron and with the secretion of renin, an enzyme involved in the formation of angiotensin II. Structures within the capsular space (Bowman’s capsule) appear as independent structures because of the transverse section view. Structurally, they are continuous with each other and with the afferent and efferent arterioles. (From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 11-12 Functional nephron and processes involved in urine formation. The arrows indicate the origins and destinations of the three processes associated with the formation of urine. After glomerular filtration, glomerular filtrate enters the proximal tubule and becomes tubular fluid. Tubular secretion is directed from the peritubular capillaries into the tubules and tubular reabsorption is directed from the tubules into the peritubular capillaries. Tubular reabsorption and tubular secretion occur throughout the length of the nephron.

Figure 11-13 Dynamics of glomerular filtration in mammals. Bowman’s capsule is separated from the glomerulus by a glomerular membrane, through which filtration occurs. The extent of filtration is determined by the difference between the pressures favoring filtration and those opposing filtration. In this illustration, filtration occurs because 60 - (32 + 18) = 10 mm Hg. Values greater than or less than 10 mm Hg would correlate with more or less filtration, respectively. Pressure values (60, 32, 18) are in mm Hg. P_c is capillary hydrostatic pressure; Pbs is Bowman’s space hydrostatic pressure; and π_c is colloidal osmotic pressure.

Figure 11-14 The conversion of angiotensinogen to angiotensin II. Plasma angiotensinogen is produced in the liver. It is converted to angiotensin I by renin released from the juxtaglomerular cells of the afferent and efferent arterioles. Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE) derived from capillary endothelium.

Figure 11-15 Structures that separate tubular fluid in the tubular lumen from plasma in peritubular capillaries. The energy requirement for reabsorption and secretion processes is provided by the Na⁺-K⁺-ATPase (“sodium pump”) located in the basolateral membrane of proximal tubule epithelial cells.

Figure 11-16 Transport of Na⁺ from tubular lumen into the tubular epithelial cell and its cotransport with glucose. The protein carrier conformation permits reception of Na⁺ and glucose from the lumen. Carrier conformational change permits Na⁺ and glucose release into the epithelial cytoplasm. Once released, the carrier returns to its original conformation for the reception of more Na⁺ and glucose. The Na⁺ released into the tubular epithelial cytoplasm is actively transported through the basal and lateral borders of the cells into the ISF and diffuses from there into the capillaries. Glucose follows the same pathways except that it is not actively transported. Amino acids are also cotransported with Na⁺ similar to that of glucose.

Figure 11-17 Countercurrent multiplication in the loop of Henle and recirculation of urea. Values shown (in milliosmoles per kilogram H₂O) are hypothetical but approximate those of humans under conditions of low water intake. Single numbers represent total osmolality. Identified numbers (NaCl, urea) represent a specific contribution to total osmolality. Transport of NaCl and urea at the level of the thin segment of the ascending limb of the loop of Henle is by simple diffusion. Active transport of Na⁺ in the ascending thick limb is coupled with the transport of Cl^- (cotransport). Water channels (also urea) on the right are open (influence of antidiuretic hormone). In this example, urine is being concentrated. Circled numbers identify locations as follows: (1) descending limb of the loop of Henle; (2) thin segment of ascending limb of loop of Henle; (3) thick segment of ascending limb of the loop of Henle; (4) cortical collecting duct; (5) outer medullary collecting duct; (6) inner medullary collecting duct. See text for details. (From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 11-18Countercurrent exchange in vasa recta. Values shown (milliosmoles per kilogram H₂O) approximate those of humans. Blood enters from the cortex near circled number 1 with a milliosmolality of about 300 and descends through an increasingly hypertonic peritubular fluid in the medulla (circled number 2). Water diffuses out and solute diffuses in until the hairpin turn is reached (circled number 3). The blood then ascends through decreasing hypertonicity, and water diffuses in and solute diffuses out (circled number 4). When blood returns to the cortex (circled number 5), the milliosmolality is only slightly higher than when it entered the vasa recta. (From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 11-19 Relationships among the hypothalamus, posterior pituitary, and kidneys in the regulation of extracellular hydration. (1) Extracellular dehydration detected by osmoreceptors in the hypothalamus. Boxed area in 1 shows the location in the brain of the boxed area in 2. (2) ADH Cneurosecretion of supraoptic nuclei in hypothalamus) secreted into blood in response to dehydration. (3) Cortical collecting tubules and medullary collecting ducts are targets of ADH, causing increased reabsorption of H₂O.

Figure 11-20 Cycle of events for the relief of hyperosmolality. Increased thirst is the predominant factor for the correction of hyperosmolality. ADH, antidiuretic hormone. (From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th 2dn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 11-21 Renal and cardiovascular responses induced by the sympathetic division of the autonomic nervous system in response to reduced circulating volume (hypovolemia). Efferent renal sympathetic nerve activity (ERSNA) responses are graded depending on the severity of hypovolemia. Accordingly, renin secretion is the first response, followed by tubular Na⁺ reabsorption, and finally vasoconstriction to alleviate declining blood pressure associated with hypovolemia. ADH, antidiuretic hormone. (From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 11-22 Relationship of parathyroid hormone (PTH), the kidneys, and calcium ion homeostasis in the cow. PTH from the parathyroid gland activates vitamin D in the kidney; activated vitamin D promotes absorption of Ca²⁺ from the intestine.

Figure 11-24Mechanism for the renal secretion of H⁺ associated with the phosphate buffer system in the tubular fluid.

Figure 11-25Mechanism for the secretion of H⁺ associated with the secretion of ammonia by the tubular epithelial cells.

Figure 11-26Ventral view of organs and associated structures of the dorsal abdominal cavity of a rooster (male chicken). A, abdominal aorta; AE, epididymal artery; AR, cranial renal artery; C, cloaca; E, epididymis; EI, external iliac vein; P, caudal renal portal vein; R, renal vein; T, testis; TA, testicular artery; U, ureters; V, caudal vena cava; VD, ductus deferens; 1, 2, and 3, cranial, middle, and caudal lobes of the left kidney, respectively. (From Hodges R. The Histology of the Fowl. New York: Academic Press, 1974.)

Figure 11-23 Mechanism for the renal secretion of H⁺ associated with the bicarbonate buffer system in the tubular fluid.

Figure 11-27Arrangement of reptilian and mammalian nephrons within a lobule. (1) An avian kidney with its three lobes. (2) A number of lobules from a lobe. (3) The inner structure of a lobule. Reptilian nephrons do not have loops of Henle. Mammalian nephrons are located near the medullary cone and extend their loops of Henle into the cone. The tubular fluid from both nephron types is received by common collecting ducts that also extend into the medullary cone, where it is exposed to ISF concentration gradients similar to mammalian kidneys. All urine from a lobule leaves by a common ureteral branch.

Figure 11-28 The location of avian reptilian-type (RT) and mammalian-type (MT) nephrons relative to an intralobular central vein (cv) and a perilobular collecting tubule (pct). The intermediate segment of the RT nephron and the nephron loop of the MT nephron are shown in black. The finely stippled areas are beginning collecting tubules. (From Johnson O. Urinary organs. In: King A, McClelland J, eds. Form and Function in Birds. San Diego: Academic Press, 1979.)

Figure 11-29The vasa recta and associated capillary plexus from an avian kidney medullary cone. Microfill injection via ischiadic artery. (From Johnson O. Urinary organs. In: King A, McClelland J, eds. Form and Function in Birds. San Diego: Academic Press, 1979.)

Figure 11-30 The veins associated with the renal portal system of birds. Blood arrives from the hindlimbs via the external iliac and sciatic veins. Also shown is a renal portal valve. Its closure has potential for diverting more blood to the renal portal system. (From Sturkie PD. Kidneys, extrarenal salt excretion, and urine. In: Sturkie PD, ed. Avian Physiology. 4th edn. New York: Springer-Verlag, 1986.)

Figure 11-31 Intralobular blood flow. Intralobular artery (ia) blood supplies afferent arterioles (aa) going to glomeruli (g). Blood leaving the glomeruli via,efferent arterioles (ea) enters the peritubular capillaries and mixes with blood from branches of the renal portal (RP) veins. Peritubular blood enters the central vein (CV) of each lobule. Arrows indicate the direction of blood flow. (From Johnson O. Urinary organs. In: King A, McClelland J, eds. Form and Function in Birds. San Diego, CA: Academic Press, 1979.)

Chapter 12

Figure 12-1Comparisons of gastrointestinal tracts of the dog (A), of the horse (B), and of cattle (C). (1) Stomach; (2) small intestine; (3) cecum; (4) ascending colon in dog, large colon in horse, coiled colon (ansa spiralis) in cattle; (5) descending colon. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 2nd edn. Philadelphia: WB Saunders, 1996.)

Figure 12-2 Schematic transverse section of the upper and lower jaws of the horse between the third and fourth molars showing the position of the tables of the teeth during rest and mastication. 1. Position of the teeth during rest. The outside edge of the lower row is in apposition with the inside edge of the upper. 2. Jaws fully crossed, masticating from left to right (lower jaw movement). The tables of both right upper and lower molars now rest on each other. 3. Position halfway through mastication. The outer half of the right lower tooth wears against the inner half of the right upper. Note the potential for developing “points” on the cheek side of the uppers and on the tongue side of the lowers. Right lower jaw movement followed by left lower jaw movement. UJ, upper jaw; LJ, lower jaw; RM, right molar; LM, left molar; RLM, right lower molar; LLM, left lower molar. (From Smith F. Manual of Veterinary Physiology. 5th edn. Chicago, IL: Alexander Eger, 1921.)

Figure 12-3 Incisors of the horse showing wear characteristics. A. Longitudinal section. B. Transverse section. C. Table surfaces: 1 = full mouth and incisors in wear; 2 = cups are gone; 3 = older horse showing the loss of the enamel spot and change in the dental star and table surface shape. I1 = Central incisors,,I2 = Intermediate incisors, I3 = Corner incisors. Approximate age of appearance shown in years by corresponding numbers on right, for C1 and C2.

Figure 12-4 A view of the dorsal surface (dorsum linguae) of a bovine tongue with special emphasis on its roughness provided by the papillae. Conical papillae are dominant on the prominence. Rostral to the prominence are large and horny filiform and conical papillae with sharp points directed caudally. These papillae impart to the tip its rasp-like roughness and make it very efficient in the prehension of food. One-half of the tongue is shown without filiform and conical papillae for contrast.

Figure 12-5 The respective relationship of the nasal and oral cavities to the pharynx during respiration and deglutition. Reflexes associated with deglutition facilitate the safe passage of food from the oral cavity pharynx into the esophagus. (Modified from Frandson RD, Spurgeon TL. Anatomy and Physiology of Farm Animals. Malvern, PA: Lea & Febiger, 1992.) Figure 12-6 Parts of the canine stomach.

Figure 12-7 Inner regions of the stomach in the horse, pig, and ruminant. E, Nonglandular region; C, cardiac gland region; F, fundic gland region; P, pyloric gland region. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames IA: Wiley-Blackwell, 2009.)

Figure 12-8Dorsal view of the canine stomach, duodenum, and pancreas. 1, Right lobe of pancreas; 2, body of the pancreas; 3, left lobe of pancreas; 4, pancreatic ducts. The common bile duct is received into the duodenum in close association with the pancreatic duct. (From Adams DR. Canine Anatomy: A Systemic Approach. Ames, IA: Iowa State University Press, 1986.)

Figure 12-9 Schematic representation of the general organizational features of the mammalian gastrointestinal tract. A. Cross-section of the small intestine with its mesenteric suspension that envelops the intestine as its serosa. B. Boxed section from A to show greater detail. Auerbach’s nerve plexus controls gastrointestinal movements. Meissner’s plexus (not shown) is in the submucosa, and controls secretions and blood flow. The muscularis mucosae produces folds in the mucosa for amplification of the surface area.

Figure 12-10 A layered section of intestine as viewed from its inner surface. The folds are produced by strategic contraction of the muscularis mucosae. The projections from the surface represent the villi, another means of surface amplification.

Figure 12-11 Photomicrograph of microvilli extending from a small intestine epithelial cell. The cord-like structures extending downward from the microvilli are contractile actin filaments. (From Fawcett DW. Bloom and Fawcett: A Textbook of Histology. 11th edn. Philadelphia, PA: W.B. Saunders, 1986. Courtesy of N. Hirokawa and J. Heuser.)

Figure 12-12 Three-dimensional representation of the small intestine lining. The villi are finger-like processes with cores of lamina propria that extend into the lumen. The crypts of Lieberkuhn,are depressions into the lamina propria (Lp). (From Ham AW. Histology. 7th edn. Philadelphia, PA: J.B.,Lippincott, 1974.)

Figure 12-13 Functional organization of the villus: A. Longitudinal section. B. Cross-section showing the epithelial cells and basement membrane. (From Guyton AC. Textbook of Medical Physiology. 8th edn. Philadelphia, PA: WB Saunders, 1991.)

Figure 12-14Dorsal view of the dog cecum and colon (large intestine). The dog, a carnivore, has no special arrangement for its ascending colon. The rectum is the pelvic portion of the descending colon that terminates at the anus.

Figure 12-15Schematic representation of the intestinal tract of the pig. 1, Rectum; 2, cecum; 3, ileum; 4, ansa spiralis (coiled colon); 5, descending colon; 6, transverse colon; 7, second curve of duodenum; 8, jejunum. (From Engel HH, St Clair LE. Anatomy. In: Leman AD, et al., eds. Diseases of Swine. 6th edn. Ames, IA: Iowa State University Press, 1986.)

Figure 12-16Gastrointestinal tract of the cow showing the colic spiral (ansa spiralis). (From Dyce KM, Wensing CJG. Essentials of Bovine Anatomy. Philadelphia, PA: Lea & Febiger, 1971.)

Figure 12-17Schematic representation of the cecum and colon of the horse. (From Getty R. Sisson and Grossman’s Anatomy of the Domestic Animals. 5th edn. Philadelphia, PA: WB Saunders, 1975.)

Figure 12-21Portion of a liver lobule (highly magnified). Blood from the portal vein and hepatic artery flows into sinusoids (lined with Kupffer cells) and empties into the central vein. Bile travels in the opposite direction in canaliculi to empty into bile ducts in the triad areas. (From Ham AW. Histology. 7th edn. Philadelphia, PA: JB Lippincott, 1974.)

Figure 12-18 Location of salivary glands in the dog. They are paired glands and only those on the right side are shown. The right mandible has been removed to show the sublingual salivary gland and its duct. The duct empties on a small papilla located near the rostral end of the frenulum (midventral fold of the tongue).

Figure 12-19Location of the pancreas and its general appearance. The pancreas is always located near the first part of the duodenum and appears as an elongated gland of loosely connected aggregated nodules. The inset from the pancreas shows an islet of Langerhans (endocrine) situated among a number of pancreatic acini, the exocrine (digestive secretions) portion.

Figure 12-20 The pig liver and its location relative to other organs. Because of the large amount of interlobular connective tissue, the lobules are mapped out sharply. For this reason, the liver is much less friable (easily broken) than that of other animals.

Figure 12-22Chemical structure of monosaccharides are represented by glucose and galactose.

Figure 12-23Chemical structure of disaccharides as represented by maltose and sucrose.

Figure 12-24 Schematic representation of the highly branched glycogen molecule. Each bead of the chain represents a glucose molecule. (From Conn EE, Stumpf PK. Outlines of Biochemistry. New York: John Wiley & Sons, 1963.)

Figure 12-25 A polypeptide chain, the basic primary structure of a protein. The peptide bonds are shown by the areas boxed by dashed lines.

Figure 12-26 Hydrolysis of a simple lipid. Three molecules of long-chain fatty acids and one molecule of glycerol are released when a triglyceride molecule is hydrolyzed. The great majority of lipids are triglycerides. Lipids are esters of glycerol and fatty acids. The ester linkages are shown within the area circumscribed by the dashed lines.

Figure 12-27Sphingomyelin. This phospholipid is common to myelin sheaths of nerve fibers.

Figure 12-28 Chemical structure of cholesterol.

Figure 12-29 Displacement of structures associated with swallowing a food bolus. A. A food bolus is moved through the oral cavity and plunged into the pharynx near the root of the tongue during the voluntary stage of swallowing. This begins the reflex stages. B. Pharyngeal stimulation leads to inhibition of respiration and closing of the glottis (opening to the larynx and trachea). The caudal direction of the root of the tongue elevates the soft palate, closing off the nasal cavity, and the epiglottis, further sealing the glottis. Pharyngeal contraction forces the food bolus into the esophagus. C. A peristaltic reflex is initiated by the presence of the food bolus in the esophagus; the bolus is transported to the stomach by peristalsis; pharyngeal structures return to the normal position.

Figure 12-30 Membrane potentials in mammalian intestinal smooth muscle. Note the slow waves, spike potentials, and directions of depolarization and hyperpolarization. (From Guyton AC, Hall JE. Textbook of Medical Physiology. 10th edn. Philadelphia, PA: WB Saunders, 2000.)

Figure 12-31 Segmentation contractions of the small intestine. Movement of chyme into the receiving (relaxed) segment by the propulsive (contracting) segment results in mixing. The receiving segment then becomes the propulsive segment and mixing continues. (From Rhoades RA, Tanner GA. Medical Physiology. 2nd edn. Baltimore, MD: Lippincott Williams & Wilkins, 2003.)

Figure 12-35 The major mammalian gastrointestinal hormones and their association with gastric, pancreatic, and biliary secretions. A. Gastrin: 1, stimulates secretion of HCOo^- and H₂O from bile duct epithelium; 2,,stimulates HCl and pepsinogen secretion; 3, stimulates secretion of pancreatic enzymes. B. Secretin: 4, inhibits HCl secretion and stimulates pepsinogen secretion;,5, stimulates secretion of HCOo^- and H₂O from pancreas; 6, stimulates secretion of HCO3^- and H₂O from bile duct epithelium. C. Cholecystokinin: 7, inhibits HCl secretion; 8, stimulates secretion of pancreatic enzymes; 9, stimulates contraction of gallbladder and relaxation of sphincter of Oddi, and stimulates secretion of HCO₃^- and H₂O by bile duct epithelium.

Figure 12-32 Intestinal peristalsis and movement of contents. A. Original distention. B. Contraction occurs cranial (oral) to the distention and relaxation caudal (aboral) to the distention. C. Contraction and relaxation followed by movement of contents in an aboral direction. D. A new distention point initiates a new locus of contraction and relaxation, which continues aborally as a wave.

Figure 12-33 Mechanism of hydrochloric acid secretion by parietal cells of the gastric mucosa. Carbonic anhydrase facilitates the formation of H₂CO₂ from CO₂ that diffuses into the cells from the interstitial fluid. H₂CO3 dissociates into H⁺ and HCO₂^-. H⁺ and Cl^-are actively secreted by the parietal cells into the lumen of the stomach, and this causes a gradient for diffusion of Cl^- from the plasma. The loss of Cl^- from plasma is followed by diffusion of HCO₂^- into plasma so that electrical neutrality is maintained. Accordingly, plasma bicarbonate concentration increases after ingestion of food, associated with the secretion of HCl into the lumen of the stomach.

Figure 12-34 Schematic representation of the microstructure of a liver lobule and its association with bile secretion. Most of the bile salts are reabsorbed from the intestine by active transport (others are lost in feces), enter the portal vein, and pass to the liver (enterohepatic circulation). They are quickly absorbed from the sinusoids into the liver cells and are then resecreted into the bile canaliculi by active transport. The bile salts then enter the bile duct from the canaliculi. Small amounts of bile salts are secreted continuously by the liver cells, and this accounts for that which is lost in the feces. The secretion of bile by the liver is stimulated by the amount of bile salts being recirculated. Therefore, the larger the amount recirculated, the higher the rate of bile secretion. (From Guyton AC, Taylor AE, Granger HJ. Dynamics and Control of the Body Fluids. Philadelphia, PA: WB Saunders, 1975∙)

Figure 12-36 Chemical structure of principal volatile fatty acids derived from fermentation in the rumen and large intestine. A. Two carbon atoms. B. Three carbon atoms. C. Four carbon atoms.

Figure 12-37The stomach of cattle (left view). The rumen and reticulum (shown) are two of the three compartments of the forestomach that precede the true stomach (abomasum). The reticulo-omasal orifice is the passageway to the third compartment known as the omasum. The rumen is divided into a number of sacs by muscular pillars. Pillar contraction is essential for movement of rumen content. The dashed line illustrates the extent of the rib cage.

Figure 12-38 The stomach of cattle (right view). The omasum is the third compartment of the forestomach, which has a short omasal canal that connects the reticulo-omasal orifice with the omaso-abomasal orifice. The dashed line illustrates the extent of the rib cage.

Figure 12-39 Relative sizes of the bovine stomach compartments at various ages. A. Three days old. B. Four weeks old. C. Three months old. D. Adult. a, Rumen; b, reticulum; c, omasum; d, abomasum. (From Nickel,R, Schummer A, Seiferle E. The Viscera of the Domestic Mammals. 2nd edn. Berlin: Verlag Paul Parey, 1979.)

Figure 12-40 “Bill,” a Jersey steer with a large rumen fistula. The animal was born in May 1942, the fistula was made in March 1943, and, after a leg injury, the steer was euthanized in January 1955. This photograph was taken in June 1954. When not in use, the fistula was kept closed with a pneumatic plug. (From Dukes HH. The Physiology of Domestic Animals. 7th edn. Ithaca, NY: Cornell University Press, 1955. Used by permission of the publisher, Cornell University Press.)

Figure 12-41 Tracings showing the mechanism of regurgitation in rumination. The writing points were vertically placed. The cow regurgitated at X. 1. Movements of air in the nostrils. Note closure of the glottis from a to b. 2. Movements of the jaw in mastication. Note the pause from c to d. 3. Movements of boluses in the cervical part of the esophagus: e, the masticated bolus; f, the regurgitated bolus; g, h, the swallowed liquid pressed out of the regurgitated bolus. 4. Time tracing showing 1-second intervals. 5. Movements of the thoracic wall. 6. Rectal pressure. It is not elevated during regurgitation. 7. Pressure changes in the trachea. A sharp decrease coincident with regurgitation is seen. The increase in pressure as it is caused by the momentum of the liquid (bromoform) used in the recording manometer. (From Bergman HD, Dukes HH. An experimental study of the mechanism of regurgitation in rumination. J Am Vet Med Assoc. 1926; 69: 600.)

Figure 12-42 Radioactivity in blood and saliva of the goat after intraruminal insufflation with CO₂. (From Dougherty RW, Mullinax CH, Allison MJ. Physiological disposition of ¹⁴C- labeled rumen gas in sheep and goats. Am J Physiol. 1964; 207: 1185.)

Figure 12-43 Major metabolic pathways in the ruminant liver. Because insufficient glucose is absorbed, one of the main functions of the liver is gluconeogenesis. These reactions are shown by heavy arrows; four major pacemaker reactions are indicated by asterisks. TCA, tricarboxylic acid. (From Bergman EN. Disorders of carbohydrate and fat metabolism. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 11th edn. Ithaca, NY: Cornell University Press, 1993. Used by permission of the publisher, Cornell University Press.)

Figure 12-44 Citric acid cycle (tricarboxylic acid cycle, Krebs cycle) in relation to ruminant metabolism. Only major intermediates are shown. (1) Produced by ruminal fermentation; (2) pathway established in rumen epithelium; (3) arginine, proline, hydroxyproline, and histidine probably enter the citric acid cycle after conversion to glutamate, while aspartate gives rise to oxaloacetate by transamination; (4) the glycerol arising from the breakdown of neutral fat is metabolized by the glycolytic pathway. (From Annison EF, Lewis D. Metabolism in the Rumen. New York: John Wiley & Sons, 1959.)

Figure 12-45Digestive tract of a turkey. 1, Precrop esophagus; 2, crop; 3, postcrop esophagus; 4, glandular stomach (proventriculus); 5, isthmus; 6-9, muscular stomach (gizzard); 10, proximal duodenum; 11, pancreas; 12, distal duodenum; 13, liver; 14, gallbladder; 15, jejunum; 16, Meckel’s diverticulum (remnant of yolk sac); 17, ileocecocolic junction; 18, ceca; 19, colon; 20, bursa of Fabricius; 21, cloaca; 22, vent. See text for description of the various parts. (From Duke G. Avian digestion. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 11th edn. Ithaca, NY: Cornell University Press, 1993. Used by permission of the publisher, Cornell University Press)

Figure 12-46 Median section of the cloaca of a 6-month-old female domestic fowl. 1, Colon; 2, coprodeum; 3, urodeum; 4, proctodeum; 5, vent; 6, cloacal bursa; 7, position of oviduct bursa, on left side only; 8, ureteric orifice. (From Reece WO, Trampel DW. Avian digestion. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals, 13th edn. Ames, IA: Wiley- Blackwell, 2015.)

Chapter 13

Figure 13-1Diurnal temperatures in the watered and dehydrated camel. The rectal temperature elevations (heat storage) occur during the day and the reductions occur at night. (From Schmidt-Nielsen K. Osmotic regulation in higher vertebrates. In: The Harvey Lectures, 1962-1963, Series 58. London: Academic Press, 1963.)

Figure 13-2 Schematic section of dog skin showing the extensive network of blood vessels and the location of insulating adipose tissue. (From Evans HE. Miller’s Anatomy of the Dog. 3rd edn. Philadelphia, PA: WB Saunders Company, 1993.)

Figure 13-3 Response of warmth-sensitive neurons (solid line) in the rostral hypothalamus of the cat to increasing hypothalamic temperature. Neurons insensitive to warmth (dashed line) do not increase their activity. (From Nakayama T, Hammel HT, Hardy JD, Eisenman JS. Thermal stimulation of electrical activity of single units of the preoptic region. Am J Physiol. 1963; 204: 1122.)

Figure 13-4 Schematic representation of apocrine and sebaceous glands and their association with a hair follicle. The secretory parts of the apocrine glands are located in the dermal and subcutaneous layers of the skin. The excretory ducts pass upward through the dermis and empty into the hair follicles above the ducts of the sebaceous glands.

Chapter 14

Figure 14-1 Genital organs of the bull. 1, Seminal vesicle; 2, ampulla of vas deferens; 3, bladder; 4, urethral muscle surrounding pelvic urethra; 5, bulbospongiosus muscle; 6, ischiocavernosus muscle; 7, retractor penis muscle; 8, glans penis; 9, preputial membrane and cavity. (From Roberts SJ. Veterinary Obstetrics and Genital Diseases [Theriogenology]. 3rd edn. Woodstock, VT: Stephen J. Roberts, 1986.)

Figure 14-2 Detailed structure of the testicle. Only two of the many seminiferous tubule loops are shown. Testicular fluid is secreted by Sertoli cells into the lumen of the seminiferous tubules. Myoid cells are contractile cells contained within the basement membrane. (From Hafez ESE, Hafez B. Reproduction in Farm Animals. 7th ed,. Baltimore, MD: Lippincott Williams & Wilkins, 2000.)

Figure 14-3 Relationship of the seminiferous tubules to each other and to the interstitial tissue. The interstitial tissue is occupied not only by the usual blood vascular network but also by Leydig cells (interstitial cells) and by connective tissue septa (provides support for seminiferous tubules) from the connective tissue capsule (tunica albuginea) of the testis.

Figure 14-4Schematic representation of the periphery of a seminiferous tubule. The Sertoli cells divide the seminiferous tubule into adluminal and basal compartments at their basal junction (tight junction). Leydig cells are in the interstitial space. The basal junction forms a blood-testis barrier whereby the tubule environment is controlled and spermatozoa are prevented from entering the interstitium.

Figure 14-5 Relationship of the seminiferous tubules to the rete testis, efferent ducts, epididymis, and ductus deferens. The rete testis is a network of straight tubules connecting convoluted seminiferous tubules with the highly convoluted epididymal tubule via efferent ducts (extratesticular). The flow of spermatozoa with their fluids is shown by the arrows.

Figure 14-6Cross-section of the spermatic cord of mammals. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley- Blackwell, 2009.)

Figure 14-7The descended adult testis featuring its relationship to the enveloping visceral vaginal tunic, spermatic cord, the inguinal canal, deep and superficial inguinal rings, vaginal

cavity, and peritoneal cavity. The vaginal ring is the location where the parietal vaginal tunic of the scrotum is continuous with the parietal peritoneum. The proper ligament of testis and ligament of tail of epididymis are remnants of gubernaculum testis.

Figure 14-8 Disposition of the accessory glands that discharge into the pelvic urethra of the bull.

Figure 14-9Comparative anatomy of the male reproductive organs of various domestic animals. A. Dog. B. Ram. C. Boar. D. Stallion. Note the encirclement of the pelvic urethra by the prostate in the dog, urethral process in the ram, preputial diverticulum in the boar, and double-folded prepuce in the stallion.

Figure 14-10 A. Transverse sections of the fibroelastic penis of a bull. B. the musculocavernous penis of a stallion. 1,. Tunica albuginea; 2, corpus cavernosum; 3, septum; 4, urethra; 5, corpus spongiosum; 6, bulbospongiosus; 7, retractor penis; 8, large, thick­walled veins. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 3rd edn. Philadelphia, PA: WB Saunders, 2002.)

Figure 14-11“Locking” phase, or “tie”, of canine coitus (lateral view). In the dog, erection involves primarily the glans penis. Enlargement of the bulbus glandis and contraction of vestibular muscles during intromission “lock” the dog’s penis in the bitch’s vagina.

Figure 14-12Penis of the bull. A. Nonerect position with its characteristic sigmoid flexure. B. Erect position with elimination of the sigmoid flexure and extension beyond the prepuce. The retractor penis muscle assists return of the penis to its nonerect position.

Figure 14-13Penis of the bull and some of its associated muscles. The bulbospongiosus muscle assists in emptying the urethra. The ischiocavernosus muscle assists in the erection process and the retractor penis muscle assists in the return of the penis to the prepuce after intromission.

Figure 14-14 Lateral view of the stallion testis with emphasis on the pampiniform plexus. The pampiniform plexus is illustrated by the intertwining of the testicular artery and vein. This allows for the cooler venous blood to cool the warmer arterial blood going to the testis. Also, closeness of testicular arteries and veins to the testicular surface favors direct loss of heat from the testes.

Figure 14-15 Diagrammatic representation of the stages of spermatogenesis in mammals. The chromosome number (2n, diploid; n, haploid) is also shown for each stage. (From Pineda MH. The biology of sex. In: Pineda MH, Dooley MP, eds. Veterinary Endocrinology and Reproduction. 5th edn. Ames, IA: Iowa State Press, 2003.)

Figure 14-16 Comparison of the spermatozoa of farm animals and other vertebrates. The major structural features are given. Note the differences in the relative size and shape. (From Hafez ESE, Hafez B. Reproduction in Farm Animals. 7th edn. Baltimore, MD: Lippincott Williams & Wilkins, 2000.)

Figure 14-17A seminiferous tubule in which the wave of the seminiferous epithelium is schematically represented along the length of the tubule. The succession of stages I to XII (a 12-day cycle), the site of reversal in the middle of the tubule, and the relationship of the wave to the rete testis are shown. The more advanced stages of each wave are located nearer the rete testis. Any one tubule may have as many as 15 spermatogenic waves. (From Hafez ESE, Hafez B. Reproduction in Farm Animals. 7th edn. Baltimore, MD: Lippincott Williams & Wilkins, 2000.)

Figure 14-18 The urogenital system of the male chicken (ventral view). The testes are located within the body cavity and the ductus deferens conduct spermatozoa to the cloaca. (From Sturkie PD, Opel H. Reproduction in the male, fertilization, and early embryonic development. In: Sturkie PD, ed. Avian Physiology. 3rd edn. New York: Springer-Verlag, 1976.)

Figure 14-19 Lateral view of the cloaca and the terminal part of the vas deferens (ductus deferens) of the domestic fowl. The ejaculatory groove (not shown) is formed at the time of sexual excitation when the lymphatic folds become engorged with lymph, forming a trough­like structure to direct the flow of semen. The paracloacal vascular body is the source of the lymph. The receptacle of the ductus deferens serves as a storage site for spermatozoa. (From Lake PE. Male genital organs. In: King AS, McClelland J, eds. Form and Function in Birds,

Vol. 2. San Diego, CA: Academic Press, 1981.)

Chapter 15

Figure 15-1 Reproductive tract of the cow (dorsal aspect). The body of the uterus, vagina, and vulva (vestibule of the vagina) have been laid open and the right ovary withdrawn from the ovarian bursa and infundibulum. The broad ligament (a downward reflection of the peritoneum) suspends the reproductive tract from the dorsolateral abdominal wall.

Figure 15-2 Location of reproductive organs relative to the rectum and urinary bladder. A. Cow. B. Sow. C. Mare. D. Bitch. Note species differences in anatomy of the cervix and mammary gland(s). 1, rectum; 2, urinary bladder; 3, cervix; 4, uterus; 5, vagina; 6, vulva; 7, ovary; 8, mammary gland(s).

Figure 15-3 Dorsocranial view of bovine female reproductive organs. The broad ligament is the inclusive term for the mesovarium, mesosalpinx, and mesometrium, which suspend the ovary, uterine tubes, and uterus, respectively, from the dorsolateral wall of the sublumbar region. The broad ligament is a reflection from the peritoneum.

Figure 15-4 Ovarian differences resulting from species morphology and functional changes. A. Sow ovary (berry shaped). B. Cow ovary (almond shaped) with ripening follicle. C. Cow ovary with fully developed corpus luteum. D. Mare ovary (kidney shaped) with ovulation fossa (indentation on the lesser curvature). (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 3rd edn. Philadelphia, PA: WB Saunders, 2002.)

Figure 15-5 Development of an ovarian follicle from its primordial (primary) form to a Graafian follicle. Growing follicles are those that have begun growth from the resting stage as primordial follicles but have not developed thecal layers or an antrum. (From Pineda MH. Female reproductive system. In: Pineda MH, Dooley MP, eds. Veterinary Endocrinology and Reproduction. 5th edn. Ames, IA: Iowa State Press, 2003.)

Figure 15-6Genital tract comparisons among some domestic animals. 1, Uterine horn; 2, uterine body; 3, cervix; 4, urinary bladder; 5, ureter; 6, urethral opening. The genital tracts are opened dorsally near the body of the uterus, and the opening is extended caudally to the labia to show the cervix and urethral opening. Note that the relative proportions of uterine horns, uterine body, and cervix vary among species. The illustrations are not drawn to scale and do not compare size.

Figure 15-7 Relationship of the bovine fetal placenta to the maternal endometrium. A. View of fetus within the uterus showing multiple placentomes (caruncle and cotyledon together are referred to as a placentome). B. Magnification of a placentome that is surrounded by a number of endometrial gland openings. Only a part of the fetal cotyledon is shown so that the underlying maternal caruncle and endometrial gland openings can be visualized. C. Cross­section of a placentome. The contribution by the fetal placenta is known as the cotyledon and the maternal contribution is known as the caruncle.

Figure 15-8 Position of the cow’s uterus. A. The nongravid uterus (vertical striping) compared with the 6-month gravid uterus (horizontal striping). B. Location of the 6-month gravid uterus in transverse section (rumen on left and uterus on right side of abdomen). (From Dyce KM, Wensing CJG. Essentials of Bovine Anatomy. Philadelphia, PA: Lea & Febiger, 1971.)

Figure 15-9 Species variations in position of the vestibule of the vagina. A. Cow. B. Mare. C. Bitch. The vulva, and hence the vestibule of the vagina, extends caudally from the external urethral orifice. 1, Vagina; 2, bladder; 3, urethra; 4, suburethral diverticulum (not present in the mare and bitch); 5, vulva. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 4th edn. St Louis, MO: Saunders Elsevier, 2010.)

Figure 15-10 Ventral view of blood supply to the reproductive tract of the cow. The arteries are shown on the right side and the veins on the left. 1, ovarian artery; 1’, uterine branch; 2, uterine artery; 3, vaginal artery; 4, ovarian vein; 5, uterine vein; 6, vaginal vein. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 4th edn. St Louis, MO: Saunders Elsevier, 2010.)

Figure 15-11Relationship of the ovarian artery of a ruminant and its branches (1) with those of the ovarian vein (2). The intertwining ensures a large area of contact. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 3rd edn. Philadelphia, PA: WB

Saunders, 2002.)

Figure 15-12Chemical structure of some steroid hormones and diethylstilbestrol. (From Pineda MH. Female reproduction system. In: Pineda MH, Dooley MP, eds. McDonald’s Veterinary Endocrinology and Reproduction. 5th edn. Ames, IA: Iowa State Press, 2003.)

Figure 15-13Biosynthesis of steroid hormones from cholesterol. (From Hafez ESE, Hafez B. Reproduction in Farm Animals. 7th edn. Baltimore, MD: Lippincott Williams & Wilkins, 2000.)

Figure 15-14 The hypophysioportal circulation involved with the secretion of anterior pituitary hormones. Cell bodies in the hypothalamus sense the need for a hormone and secrete a releasing hormone into the hypothalamic capillary bed. The releasing hormone enters the hypophyseal capillary bed and diffuses to specific cells, causing them to secrete their specific hormone.

Figure 15-15 Formation of a Graafian follicle from a growing follicle. Wall structure. The theca interna cells are well supplied with blood. The basement membrane deprives granulosa cells of blood supply. (From Baird DT. Reproductive hormones. In: Austin CR, Short RV, eds. Reproduction in Mammals, Book 3. Cambridge, England: Cambridge University Press, 1972. Reprinted by permission of Cambridge University Press.)

Figure 15-16 Postulated route by which prostaglandin secreted by the progesterone-primed uterus can enter the ovarian artery and destroy the corpus luteum in the ewe, and possibly other species. (Adapted from Short RV. Role of hormones in sex cycles. In: Austin CR, Short RV, eds. Reproduction in Mammals, Book 3. Cambridge, England: Cambridge University Press, 1972.)

Figure 15-17 Sagittal section of an ovary. A. Primary follicle. B. Growing follicle. C. Graafian follicle. D. Ruptured follicle. E. Corpus luteum. This schematic representation shows in sequence the origin, growth, and rupture of a Graafian follicle and a corpus luteum that develops from the remains of the ruptured follicle.

Figure 15-18Effects of photoperiod on ovarian activity in the cat, horse, sheep, and goat at a latitude of 38.5° north (California). The open bars represent periods of ovarian inactivity (anestrus). The transition from anestrus to estrus (often erratic) is shown by the cross­hatched portion of the bars for the horse, sheep, and goat. (From Stabenfeldt GH, Edqvist L. Female reproductive processes. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015.)

Figure 15-19 The effect of time of insemination on conception rate in cattle. Conception rate is best when inseminated about 10 to 12 hours from beginning of estrus. (From Stabenfeldt GH, Edqvist L. Female reproductive processes. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IO: Wiley-Blackwell, 2015.)

Figure 15-20 Dorsal view of the ruminant cervix. A. The cervix has been cut open and its lateral walls reflected to show the folds and crypts. B. Magnified view of the cervix. A mucous covering assists physical entrapment of spermatozoa destined for fertilization. The folds and crypts serve as sperm reservoirs and allow for capacitation of spermatozoa.

Figure 15-21Fetus of horse within the placenta. The chorioallantois is the combination of the outer allantois with the chorion. Umbilical arteries and veins (not shown) occupy the space (blackened) between the outer allantois and chorion. The chorion is intimately associated with the endometrium. Attachment to the endometrium is not shown, and its extent varies with placental type. The inner allantois is fused with the amnion (stippled for contrast).

Figure 15-22 Diagrammatic view of persistent urachus in a foal. Failure of urachus closure at birth results in a continuous drip of urine at its umbilical exit.

Figure 15-23 Placental types according to the distribution of chorionic projections (villi) on the endometrium. A. Diffuse placenta of the horse and pig. B. Cotyledonary placenta of ruminants. C. Zonary placenta of the dog and cat. D. Discoid placenta of the human and monkey.

Figure 15-24 Estrogen patterns in the mare, cow, sow, and ewe before parturition. Negative numbers refer to days before parturition (0). (From Edqvist LE, Stabenfeldt GA.

Reproductive hormones. In: Kaneko JJ, ed. Clinical Biochemistry of Domestic Animals. 3rd

edn. New York: Academic Press, 1q8q.)

Figure 15-25 Events of parturition beginning with the prepartum secretion of fetal cortisol and ending with expulsion of the fetus. PGF_2α (prostaglandin F_2α); CL, corpus luteum.

Figure 15-26 Normal presentation for the bovine fetus, known as a cranial or anterior presentation. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2QQQ.)

Figure 15-27 The five functional regions of the oviduct of the laying hen. The oviduct is the complete tubular genitalia of the avian female and consists of the infundibulum, magnum, isthmus, uterus, and vagina.

Figure 15-28 Midsagittal section of a hen’s egg. The chalazae are extensions of the chalaziferous layer that hold the yolk and developing embryo in the center so that adhesions of the embryo to the shell membranes do not occur. The approximate percentage of the albumen for each layer is shown.

Chapter 16

Figure 16-1 Sagittal section of the cow udder through the left half. The four circular areas in the front quarter are schematically shown to illustrate the organization of the glandular tissue and also the various orders of ducts. The lobes are distributed throughout the parenchyma. The lobes are further divided into lobules (not shown). The gland cistern and teat cistern for each quarter are collectively known as the lactiferous sinus. The teat canal magnification shows the vertical folds of the teat canal and also the rosette of Furstenberg at the upper end.

Figure 16-2 Alveolus surrounded by blood vessels and myoepithelial (contractile) cells. Several alveoli in a group form a lobule. Each alveolus converges on an intralobular duct. (From Larson BL. Biosynthesis and cellular secretion of milk. In: Larson BL, ed. Lactation. Ames, IA: Iowa State University Press, 1985.)

Figure 16-3 Sagittal section through a cow’s teat. 1, Gland cistern; 2, teat cistern (gland cisterns and teat cisterns are collectively known as lactiferous sinuses); 3, openings of interlobar ducts; 4, submucosal venous ring; 5, teat canal; 6, venous plexus in teat wall; 7, streak canal (circled area is shown in Figure 16-4). (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 3rd edn. Philadelphia. PA: WB Saunders, 2QQ2.)

Figure 16-4 Section of the teat (circled area as shown in Figure 16-3) showing the smooth muscle encircling the teat canal (papillary duct). The thickened area above the teat canal, which would encircle it, is the rosette of Furstenberg. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 3rd edn. Philadelphia, PA: WB Saunders, 2QQ2.)

Figure 16-5Suspensory apparatus of the cow. The udder is shown in transverse section through hindquarters. (From Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th edn. Ames, IA: Wiley-Blackwell, 2QQQ.)

Figure 16-6Venous drainage of the udder. 1, Subcutaneous abdominal (milk) vein; 2, milk well; 3, internal thoracic vein; 4, cranial vena cava; 5, external pudendal vein (mammary vein); 6, internal pudendal vein; 6', ventral labial vein; 7, caudal vena cava; 8, diaphragm; q, costal arch; 1Q, first rib. (From Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 4th edn. St Louis, MO: Saunders Elsevier, 2Q1Q.)

Figure 16-7A 2Q-mm pig embryo, showing the milk ridge (milk line) (original magnification, ?515). (From Frandson RD, Spurgeon TL. Anatomy and Physiology of Farm Animals. 5th edn. Philadelphia, PA: Lea & Febiger, 1QQ2.)

Figure 16-8 Changes in plasma concentration of several hormones found in cows near parturition. (From Tucker HA. Endocrine and neural control of the mammary gland. In: Larson BL, ed. Lactation. Ames, IA: Iowa State University Press, 1985.)

Figure 16-9Milk letdown. Stimulation of the teats or udder results in a neuroendocrine reflex secretion of oxytocin from the posterior pituitary gland that, on reaching the myoepithelial cells, causes them to contract. (From Hafez ESE, Hafez B. Reproduction in Farm Animals. 7th edn. Baltimore, MD: Lippincott Williams & Wilkins, 2QQQ.)