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Cunningham J.G., Klein B.G.. Textbook of Veterinary Physiology. Elsevier Health Sciences,2007. — 720 ð.. 2007

Now with full-color illustrations, this easy-to-follow text takes the vast subject of physiology and focuses on concepts most important to the practice of veterinary medicine. It includes coverage of physiopathology and clinical problem-solving techniques, making this a practical resource for any practice. The book's logical, body-system organization makes it easy to find specific information. This edition includes a new chapter on cancer and a new section on the immune system.

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Contributors
Preface
Contents
The Cell
Chafter The Molecular and Cellular Basis of Physiological Regulation
Chafter Cancer: a Disease of Cellular Proliferation, Life Span, and Death
The Molecular and Cellular Basis of Physiological Regulation
KEY POINTS
Physiology is the study of the regulation of change within organisms, in this case higher animals.
All Physiological Change Is Mediated by Proteins
Protein Function Depends on Protein Shape and Shape Changes
A Series of Enzymatic Reactions Converts Tyrosine into the Signaling Molecules Dopamine, Norepinephrine, and Epinephrine
Muscle Contraction and Its Initiation and Cessation Depend on the Binding Specificity and Allosteric Properties of Proteins
Biological Membranes Are a Mosaic of Proteins Embedded in a Phospholipid Bilayer
TRANSPORT
Only Small, Uncharged Molecules and Oily Molecules Can Penetrate BiomembranesWithout the Aid of Proteins
Molecules Move Spontaneously from Regions of High Free Energy to Regions of Lower Free Energy
Important Transport Equations Summarize the Contributions of the Various Driving Forces
Starling's Hypothesis Relates Fluid Flow Across the Capillaries to Hydrostatic Pressure and Osmotic Pressure
Membrane Proteins That Serve the Triple Functions of Selective Transport, Catalysis, and Coupling Can Pump Ions and Molecules to Regions of Higher Free Energy
Many Membrane Proteins Selectively Facilitate the Transport of lons/Molecules from High to Low Electrochemical Potential
Passive Transport of K+ Across the Plasma Membrane Creates an Electrical Potential
Spatial Organization of Active and Passive Transport Proteins Enables Material to Pass Completely Through the Cell
Membrane Fusion Allows for a Combination of Compartmentalization and Transport of Material
INFORMATION TRANSMISSION AND TRANSDUCTION
Cell Signaling Usually Occurs by a Lengthy Chain of Sequential Molecular Interactions
Signaling Pathways Begin with the Binding of an Extracellular Molecule to a Receptor
Specific Physiological Information Is Inherent in the Receptor/Ligand Complex, Not in the Hormone/ Neurotransmitter Molecule
G-Protein-Coupled Receptors Are the Largest Family (a "Superfamily") of Receptors and Help Regulate Almost All Physiological Processes
Most G-Protein-Linked Information Is Sent to the Cytoplasm by "Second Messengers"
Ca2+ Transport Across Plasma and Intracellular Membranes Is an Important Second Messenger
Cyclic AMP Is Produced by Activation of a Membrane-Bound Enzyme in Response to HormoneZNeurotransmitter Binding to Receptors
The Receptor-Mediated Hydrolysis of a Rare Phospholipid of the Plasma Membrane Produces Two Different Second Messengers with Different Actions
Steroid Hormones and Other Lipid Signals Interact with Nuclear Receptors, Which Are Transcription FactorsWithin the Cell
Bibliography
PRACTICE QUESTIONS
Cancer: a Disease of Cellular Proliferation, Life Span, and Death
KEY POINTS
Traditionally, cancer was (and often still is) first detected in humans, cats, dogs, and horses by clinicians feeling for an unusual mass of cells, tumor cells.
Cancer Arises from Genetic Dysfunction in the Regulation of the Cell Cycle, Cell Life Span, and Cell Suicide
CONTROL OFTHE CELL CYCLE (PROLIFERATION)
Cell Division Is the Result of a Clocklike Cell Cycle
Cyclin-Dependent Kinases Are the "Engines" Driving the Cell Cycle
The CDK "Engines" Are Controlled by Both Throttle (Oncogene) and Brake (Tumor Suppressor) Controls
GROWTH FACTOR PATHWAY: STIMULATOR OF CELL PROLIFERATION
The Cell Cycle Is Stimulated by Growth Factors That Bind to and Activate Receptor Tyrosine Kinases
The Ras Oncogene Contributes to Many Cancers and Serves as a Model for Understanding "Small G Proteins"
The MAP Kinase Pathway Leads to the Expression of Cyclins and Other Stimulators of the Cell Cycle
The MAP Kinase Pathway Also Mediates the Stimulation of the Cell Cycle by Cell Adhesion
TUMOR SUPPRESSORS: INHIBITORS OF CELL CYCLE
Checkpoints in the Cell Cycle Are Manned by Tumor Suppressors
The Retinoblastoma and p53 Proteins Are the Main "Gatekeepers" for the Cell Cycle
MECHANISMS REGULATING CELL SUICIDE AND CELL LIFE SPAN
Apoptosis Is the Process of Cell Suicide
Resistance to Apoptosis via the Intrinsic Pathway Is a Hallmark of Cancer
Cellular Life Span Is Determined by DNA Sequences at the Ends of Chromosomes
TUMOR ORIGIN ANDTHE SPREAD OF CANCER
Cancer Cells May Be Related to Stem Cells
Death by Cancer Is Usually the Result of Its Spread, Not the Original Tumor
Growth of Solid Tumors Depends on Development of New BloodVesseIs
PROSPECTIVE CANCER THERAPY
Cancer Therapy Has a Hopeful but Challenging Future
CLINICAL CORRELATIONS
Dog That Collapsed While Running
Bibliography
PRACTICE QUESTIONS
VOCABULARY
Neurophysiology
Introduction to the Nervous System
KEY POINTS
The nervous system is the first multicellular system described in this book because it is one of the major coordinating systems of the body, and because many concepts that concern the nervous system must be clarified to understand other systems of the body.
The Neuron Is the Major Functional Unit of the Nervous System
The Mammalian Nervous System Has Two Major Subdivisions: the Central Nervous System and the Peripheral Nervous System
The Central Nervous System Can Be Divided into SixAnatomicaI Regions
The Central Nervous System Is Protected by the Meninges and Cerebrospinal Fluid
The Nervous System Collects and Integrates Sensory Information, Formulates a Response Plan, and Produces a Motor Output
CLINICAL CORRELATIONS
Neurologic Disease in a Horse
Bibliography
PRACTICE QUESTIONS
The Neuron
KEY points
There are two classes of cells in the nervous system: the neuron and the glial cell (see Chapter 3).
Neurons Have Four Distinct Anatomical Regions
Neuronal Membranes Contain a Resting Electrical Membrane Potential
The Resting Membrane Potential Is the Result of Three Major Determinants
The Resting Membrane Potential Can Be Changed by Synaptic Signals from a Presynaptic Cell
Action Potentials Begin at the Axon's Initial Segment and Spread Down the Entire Length of the Axon
CLINICAL CORRELATIONS
Hypoglycemia
Bibliography
PRACTICE QUESTIONS
The Synapse
KEY POINTS
Neurons communicate with each other and with other cells of the body, such as muscle and secretory cells.
The Anatomy of the Neuromuscular Junction Is Specialized for One-Way Communication
An Action Potential on the Presynaptic NeuronTriggers an Action Potential on the Muscle CeIIThrough the Release of Acetylcholine
There Is GreaterVariety in the Specifics of Neuron-to-Neuron Synaptic TransmissionThan in Transmission at the Neuromuscular Junction
CLINICAL CORRELATIONS
Myasthenia Gravis
Bibliography
PRACTICE QUESTIONS
The Physiology of Muscle
KEY POINTS
There are three types of muscle in the body: skeletal, cardiac, and smooth muscle.
All Movement Is the Result of Contraction of Skeletal Muscle Across a Movable Joint
There Are Several Levels of Organization in Any Skeletal Muscle
Action Potentials on the Sarcolemma Spread to the Interior of the Cell Along the Transverse Tubules
The Action Potential on the Sarcolemma Is Indirectly Coupled to the Contraction Mechanism Through the Release of Ca2+ from the Sarcoplasmic Reticulum
The Sliding of Actin Along the Myosin Molecule Results in Physical Shortening of the Sarcomere
Most Skeletal Muscle Fibers Can Be Classified as Either Fast-Contracting or Slow-Contracting Fibers
Muscles Change Their Strength of Contraction by Varying the Number of Active Motor Units or the Rate of Motor Unit Activation
The Etectromyogram Is the Clinical Measurement of the Electrical Behavior Within a Skeletal Muscle
The Structure of Cardiac and Smooth Muscle Differs from That of Skeletal Muscle
CLINICAL CORRELATIONS
Down Cow After Calving
Bibliography
PRACTICE QUESTIONS
The Concept of a Reflex
KEY POINTS
The reflex arc, the neural substrate of a reflex, is fundamental to the physiology of posture and locomotion, as well as to the clinical examination of the nervous system.
A Reflex Arc Contains Five Fundamental Components
Reflex Arcs Can Be Segmental or Intersegmental
Reflex Arcs Are Widespread in the Nervous System, and Reflexes Underlie a Major Portion of the Neurological Examination
CLINICAL CORRELATIONS
Trauma in a Foal
Bibliography
PRACTICE QUESTIONS
Skeletal Muscle Receptor Organs
KEY POINTS
Movement, characteristic of all animals, is the end product of skeletal muscle contraction.
The Muscle Spindle Stretch Receptor Is an Encapsulated Organ of SpecializedMuscle Fibers with Separate Motor and Sensory Innervations
The Muscle Spindle Conveys Information About Muscle Length to the Central Nervous System
Muscle Stretch and Action Potentials Along Spindle Sensory Neurons Lead to Reflex Contraction of the Extrafusal Muscle Fibers
The Central Nervous System Can Control Spindle Sensitivity Directly Through the Gamma (γ) Motor Neurons
The Golgi Tendon Organ Lies in Series Between Muscle and Tendon and Detects Muscle Tension
CLINICAL CORRELATIONS
Femoral Nerve Mononeuropathy
Acknowledgment
Bibliography
PRACTICE QUESTIONS
The Concept of Lower and Upper Motor Neurons and Their Malfunction
KEY POINTS
The majority of veterinary patients with neurological disease display some abnormality of posture and locomotion.
The Lower Motor Neuron Is Classically Defined as the Alpha (α) Motor Neuron
Disease of Lower Motor Neurons Causes Stereotypical Clinical Signs
Upper Motor Neurons Lie Completely in the Central Nervous System and Control Lower Motor Neurons
Signs of Upper Motor Neuron Disease Differ from Signs of Lower Motor Neuron Disease
CLINICAL CORRELATIONS
Lower Motor Neuron Disease
Upper Motor Neuron Disease
Acknowledgment
Bibliography
PRACTICE QUESTIONS
The Central Control of Movement
Key POINTS
Unlike the sensory system, which transforms physical energy into neural information, the motor system transforms neural information into physical energy.
The Central Nervous System Structures Controlling Movement Have a Hierarchical Organization
The Spinal Cord Is the Most Caudal and Simplest Level of the Movement Control Hierarchy
Brainstem Upper Motor Neuron Pathways Are the Source of All Descending Motor System Input to the Spinal Cord, Except for One Other Major Pathway
Medial and Lateral Descending Brainstem Motor Pathways Respectively Control Proximal Muscles of Posture and More Distal Muscles of Skilled Movement
The Reticulospinal and Vestibulospinal Tracts Are Medial Brainstem Motor Pathways Important for Keeping the Body Upright Against the Pull of Gravity
The Rubrospinal Tract Is a Lateral Brainstem Motor Pathway That Can Control Distal Limb Musculature Associated with Skilled Movement
The Corticospinal (Pyramidal) Tract Is a Direct Projection from Cerebral Cortex to Spinal Cord Responsible for the Most SkiIIedVoIuntaryMovements of Mammals
The Corticospinal Tract Has a Massive Lateral Component Controlling the Distal Musculature and a Minor Medial Component Controlling the Axial and Proximal Musculature
The Motor Cortices of the Frontal Lobe, the Highest Level of the Motor Control Hierarchy, Consist of Three Different Functional Regions
Corticospinal Tract Co-Activation of Both Alpha (α) and Gamma (γ) Lower Motor Neurons May Help with Small Automatic Corrections OfVoIuntary Movements
The Motor System Shares Some Organizational Principles with Sensory Systems
The Basal Ganglia and Cerebellum Modulate the Activity of Motor System Components for the Respective Selection and Adjustment of Movement
CLINICAL CORRELATIONS
Focal Lesion of the Motor Cortex
Bibliography
PRACTICE QUESTIONS
The Vestibular System
key points
To coordinate posture and locomotion, the brain needs to know not only what movement it intends to command, but also the orientation of the body and what movement the body is actually performing.
The Vestibular System Is a Bilateral Receptor System Located in the Inner Ear
Specialized Regions of the Vestibular System Contain Receptors
The Semicircular Ducts Detect Rotary Acceleration and Deceleration of the Head
The Utricle and Saccule Detect Linear Acceleration and Deceleration and Static Tilt of the Head in Space
The Vestibular System Provides Sensory Information for Reflexes Involving Spinal Motor Neurons, the Cerebellum, and Extraocular Muscles of the Eye
Vestibular Reflexes Coordinate Head and Eye Movements to MaximizeVisuaI Acuity During Movements of the Head
CLINICAL CORRELATIONS
Vestibular Syndrome
Bibliography
PRACTICE QUESTIONS
The Cerebellum
KEY POINTS
The preceding chapters, which describe the physiology of movement, discuss the function of lower motor neurons, the “final common pathway" through which the central nervous system (CNS) can initiate and control movement through the contraction of skeletal muscle.
The Cerebellum Constantly Compares the Intended Movement with the Actual Movement and Makes Appropriate Adjustments
Cerebellar Histology and Phylogeny Give Clues to Cerebellar Function
Thevestibulocerebellum Helps Coordinate Balance and Eye Movements
The Spinocerebellum Helps Coordinate MuscIeTone as Well as Limb Movement
The Cerebrocerebellum Helps with Planning Coordinated, ProperIyTimed Movement Sequences
Cerebellar Disease Causes Abnormalities of Movement
CLINICAL CORRELATIONS
Cerebellar Hypoplasia
Newborn Calf Unable to Rise
Bibliography
PRACTICE QUESTIONS
The Autonomic Nervous System and Adrenal Medulla
KEY POINTS
The autonomic nervous system (ANS) is a part of the nervous system that is generally not under conscious control.
TheAutonomic Nervous System Differs from the Somatic Motor System in at Least Two ImportantWays
The Autonomic Nervous System Has Two Major Subdivisions
The Sympathetic Nervous System Arises from the Thoracolumbar Spinal Cord
The Parasympathetic Nervous System Arises from the Brainstem and Spinal Cord
Most Autonomic Neurons Secrete Either Acetylcholine or Norepinephrine as a Neurotransmitter
Acetylcholine and Norepinephrine Have Different Postsynaptic Receptors
ThereAre General Differences in Sympathetic and Parasympathetic Function
The Autonomic Nervous System Participates in Many Homeostatic Reflexes
Preganglionic Neurons Are Influenced by Many Regions of the Brain
Loss OfAutonomic Neurons Results in the Hypersensitivity of the Target Organ to Transmitter
CLINICAL CORRELATIONS
Horner's Syndrome
Bibliography 2.
PRACTICE QUESTIONS
The Visual System
KEY POINTS
The eyes are complex sense organs that are basically an extension of the brain.
The Eye's Anatomy Is Adapted to the Eye's Role as a Visual Receptor Organ
Through the Process OfAccommodation, the Lens Changes Shape to Focus Images from Various Distances onto the Retina
The Vertebrate Retina Consists of Five Major CeIITypes
The Fovea Solves a Distortion Problem Found in OtherAreas of the Retina
Pigment Behind the Retina Either Absorbs or Reflects Light, Depending on the Animal's Habits
Photoreception and Transduction of Light Occur in the Rods and Cones
The Response of the Photoreceptor to Light Is SynapticaIIyTransmitted to the Ganglion Cells by the Bipolar Cells
The Electroretinogram Records the Electrical Response of the Retina to a Flashing Light
Ganglion CellAxonsTransmitAction Potentials to the Visual Cortex by Way of the Lateral Geniculate Nucleus
The Diameter of the Pupil Is Controlled by the Autonomic Nervous System
The Retina, Optic Nerve, and Autonomic Nerve Supply Controlling the Pupil Can BeTested with a Flashlight
Aqueous Humor Determines Intraocular Pressure
CLINICAL CORRELATIONS
Homonymous Hemianopia
Bibliography
PRACTICE QUESTIONS
Cerebrospinal Fluid and the Blood-Brain Barrier
KEY POINTS
Cerebrospinal fluid (CSF) is a clear fluid present in the ventricles (core cavities) of the brain, in the central canal that runs through the core of the spinal cord, and in the subarachnoid space that surrounds the entire outer surface of the brain and spinal cord (Figure 15-1).
Cerebrospinal Fluid Has Many Functions
Most Cerebrospinal Fluid Is Formed at the ChoroidPlexus of the Ventricles
Cerebrospinal Fluid Flows down a Pressure GradientThrough the Ventricular System into the Subarachnoid Space
Cerebrospinal Fluid Is Absorbed into the Venous System
Hydrocephalus Is an Increased Volume of Cerebrospinal Fluid in the Skull
Permeability Barriers Exist Between Blood and Brain
CLINICAL CORRELATIONS
Increased Intracranial Pressure
Seizures in a Foal
Bibliography
PRACTICE QUESTIONS
The Electroencephalogram and Sensory-Evoked Potentials
KEY POINTS
When many excitable cells are present in a living tissue, their electrical behavior can be detected by macroelectrodes placed on the body at a distance from these cells.
All Areas of the Cerebral Cortex Share Common Histological Features
The Electroencephalogram Is a Common CIinicaITooI
The Collective Behavior of Cortical Neurons Can Be Studied Noninvasively Through the Use of Macroelectrodes on the Scalp
Stimulation of Sensory Pathways Can Be Recorded as Evoked Potentials
CLINICAL CORRELATIONS
Brain Tumor
Bibliography
PRACTICE QUESTIONS
Hearing
KEY POINTS
Our lives are enriched by music and conversation and altered by the sounds of danger.
Sound Waves Are Alternating Phases of Condensation and Rarefaction (Pressure Waves) of Molecules in the External Environment
Outer and Middle Ears Funnel Sound Waves to the Cochlea
The Cochlea Is Located in the Inner Ear
The Cochlea Transduces Sound Waves to Action Potentials of the Eighth Cranial Nerve
Deciphering of Sound Wave Frequency Begins in the Cochlea
Action Potentials from the Cochlea Are Transmitted Up Through the Brainstem to the Cerebral Cortex
Deafness Results from an Interruption in the Hearing Process
CLINICAL CORRELATIONS
Congenital Deafness
Bibliography
PRACTICE QUESTIONS
Cardiovascular Physiology
Kobert B. Stepkeiuoiv
Overview of Cardiovascular Function
KEY POINTS
Because Normal Cardiovascular Function Is Essential for Life and Health, a Practical Understanding of Cardiovascular Function and Dysfunction IsVitaI to the Veterinary Clinician
Cardiovascular Dysfunctions Sometimes Reflect Primary Cardiovascular Disturbances or Diseases, but More Often They Are Secondary Consequences of Noncardiovascular Disturbances or Diseases
Substances Transported by the Cardiovascular System Include Nutrients, Waste Products, Hormones, Electrolytes, and Water
Two Modes of Transport Are Used in the Cardiovascular System: Bulk Flow and Diffusion
Because Diffusion Is Very Slow, Every Metabolically Active Cell in the Body Must Be Close to a Capillary Carrying Blood by Bulk Flow
The Pulmonary and Systemic Circulations Are Arranged in Series, but the Various OrgansWithin the Systemic Circulation Are Arranged in Parallel
Cardiac Output Is the Volume of Blood Pumped Each Minute by OneVentricIe
The Perfusion Pressure for the Systemic Circulation Is Much Greater Than the Perfusion Pressure for the Pulmonary Circulation
Each Type of Blood Vessel Has Physical Properties Suited to Its Particular Function
Blood Is a Suspension of Cells in Liquid (Plasma)
The Cellular Component of Blood Includes Red Blood CeIIsrWhite Blood Cells, and Platelets
Most of the Oxygen in Blood Is Carried in Chemical Combination with the Protein Hemoglobin Within Red Blood Cells
CLINICAL CORRELATIONS
Lethargic Kid Goat
Colic and Endotoxic Shock in Horse Secondary to Strongylus Parasitism
Bibliography
PRACTICE QUESTIONS
Electrical Activity of the Heart
KEY POINTS
Contraction of Cardiac Muscle Cells Is Triggered by an Electrical Action Potential
The Contractile Machinery in Cardiac Muscle Is Similar to That in Skeletal Muscle
Cardiac Muscle Forms a Functional Syncytium
Cardiac Contractions Are Initiated by Action Potentials That Arise Spontaneously in Specialized Pacemaker Ceils
A System of Specialized Cardiac Muscle Cells Initiates and Organizes Each Heartbeat
Cardiac Action Potentials Are Extremely Long
Membrane Calcium Channels Play a Special Role in Cardiac Muscle
The Long Duration of the Cardiac Action Potential Guarantees a Period of Relaxation (and Refilling) Between Heartbeats
Atrial Cells Have Shorter Action Potentials Than Do Ventricular Cells
Specialized Ion Channels Cause Cardiac Pacemaker Cells to Depolarize to Threshold and Form Action Potentials
Sympathetic and Parasympathetic Nerves Act on Cardiac Pacemaker Cells to Increase or Decrease the Heart Rate
Cells of the Atrioventricular Node Act as Auxiliary Pacemakers and Also Protect the Ventricles from Beating Too Fast
Sympathetic Nerves Act on All Cardiac Cells to Cause Quicker, More Forceful Contractions
Parasympathetic Effects Are Opposite to Those of Sympathetic Activation but Are Generally Restricted to the Sinoatrial Node, Atrioventricular Node, and Atria
Dysfunction in the Specialized Conducting System Leads to Abnormalities in Cardiac Rhythm (Arrhythmias)
Atrioventricular Node Block Is a Common Cause of Cardiac Arrhythmias
Cardiac Tachyarrhythmias Result Either from Abnormal Action Potential Formation (by the Sinoatrial Node or Ectopic Pacemakers) or from Abnormal Action Potential Conduction ("Reentry")
Common Antiarrhythmic Drugs Affect the Ion Channels Responsible for the Cardiac Action Potential
CLINICAL CORRELATIONS
Third-Degree Atrioventricular Block
Bibliography
PRACTICE QUESTIONS
The Electrocardiogram
KEY POINTS
An Electrocardiogram Is Simply a Graph, Made by a Voltmeter That Is Equipped to PIotVoItage as a Function of Time
Atrial Depolarization, Ventricular Depolarization, and Ventricular Repolarization Cause Characteristic Voitage Deflections in the Electrocardiogram
The Electrocardiogram Reveals the Timing of Electrical Events in the Heart
Six Standardized Electrocardiographic Leads Are Used in Veterinary Medicine
AbnormalVoltages in the Electrocardiogram Are Indicative of Cardiac Structural or Electrical Abnormalities
Electrical Dysfunctions in the Heart Cause Abnormal Patterns of Electrocardiogram Waves
CLINICAL CORRELATIONS
Dilative Cardiomyopathy with Paroxysmal Atrial Tachycardia
Bibliography
PRACTICE QUESTIONS
The Heart as a Pump
KEY POINTS
Each Heartbeat Consists OfVentricuIar Systole and Ventricular Diastole
Cardiac Output Equals Heart Rate Multiplied by StrokeVoIume
Up to a Point, Increases in End-Diastolic VentricuIarVoIume Cause Increases in Stroke Volume
End-Diastolic Ventricular Volume Is Determined by Ventricular Preload, Ventricular Compliance, and Diastolic Filling Time
Increases in Ventricular Contractility Cause Decreases in Ventricular End-Systolic Volume
Increasing the Heart Rate Does Not Increase Cardiac Output Substantially Unless StrokeVoIume Is Maintained
Murmurs Are AbnormaI Heart Sounds Caused by Turbulent FIowThrough Cardiac Defects
Some Cardiac Defects Increase the Heart's Workload, Which Causes Cardiac Hypertrophy
The Pathological Consequences of Cardiac Defects Are Direct Results of the Abnormal PressuresfVoIumes, and Workloads Created in the Cardiac Chambers
CLINICAL CORRELATIONS
Pulmonic Stenosis
Older Horse with Exercise Intolerance
Bibliography
PRACTICE QUESTIONS
The Systemic and Pulmonary Circulations
KEY POINTS
Blood Pressure Represents a Potential Energy That Propels Blood Through the Circulation
Vascular Resistance Is Defined as Perfusion Pressure Divided by Flow
The Net Resistance of the Systemic Circulation Is Called the Total Peripheral Resistance
Arterial Pressure Is Determined by the Cardiac Output and the Total Peripheral Resistance
The Blood Flow to Each Organ Is Determined by the Perfusion Pressure and the Vascular Resistance
The Pulmonary Circulation Offers Much Less Resistance to Blood Flow Than Does the Systemic Circulation
Arterial Pressures Are Measured in Terms of Systolic, Diastolic, and Mean Levels
Pulse Pressure IncreasesWhen the StrokeVoIume Increases, Heart Rate Decreases, Aortic Compliance Decreases, or Total Peripheral Resistance Increases
CLINICAL CORRELATIONS
Canine Heartworm Disease with Pulmonary Embolism
Dummy Foal: Hypoxemic Ischemic Encephalopathy
Bibliography
PRACTICE QUESTIONS
Capillaries and Fluid Exchange
KEY POINTS
Capillaries, the Smallest Blood Vessels, Are the Sites for the Exchange of Water and Solutes Between the Bloodstream and the Interstitial Fluid
Lipid-Soluble Substances Diffuse Readily Through CapilIaryWaIIsrWhereas Lipid- Insoluble Substances Must PassThrough Capillary Pores
Fick's Law of Diffusion Is a Simple Mathematical Accounting of the Physical FactorsThat Affect the Rate of Diffusion
Water Moves Across CapiIIaryWaIIs Both by Diffusion (Osmosis) and by Bulk Flow
The Starling Equation Quantifies the Interaction of Oncotic and Hydrostatic Forces Acting on Water
Several Common Physiological Changes Alter the Normal Balance of Starling Forces and Increase the Filtration of Water Out of Capillaries
Edema Is a Clinically Noticeable Excess of Interstitial Fluid
CLINICAL CORRELATIONS
Acute Protein-Losing Enteropathy in a Horse
Bibliography
PRACTICE QUESTIONS
Local Control of Blood Flow
KEY POINTS
Vascular Resistance Is Affected by Intrinsic and Extrinsic Control Mechanisms
Metabolic Control of Blood Flow Is a Local MechanismThat Matches the Blood Flow of a Tissue to Its Metabolic Rate
Autoregulation Is a Relative Constancy of Blood Flow in an Organ Despite Changes in Perfusion Pressure
Many Chemical SignaIsAct Locally (as Paracrines) to Exert Important Control on Vascular Resistance
Regardless of the Status of Arterioles, Mechanical Compression Can Reduce Blood Flow to a Tissue
CLINICAL CORRELATIONS
Patent Ductus Arteriosus
Bibliography
PRACTICE QUESTIONS
Neural and Hormonal Control of Blood Pressure and Blood Volume
KEY POINTS
Neurohumoral Mechanisms Regulate Blood Pressure and BloodVoIume to Ensure Adequate Blood Flow for All Body Organs
The Autonomic Nervous System Affects the Cardiovascular SystemThrough the Release of Epinephrine, Norepinephrine, and Acetylcholine
The Arterial Baroreceptor Reflex Regulates Arterial Blood Pressure
The Atrial Volume Receptor Reflex Regulates Blood Volume and Helps to Stabilize Blood Pressure
The Cardiovascular State of Conscious Subjects Is Determined by an Ongoing and Ever-Changing Mixture of Reflex Effects and Psychogenic Responses
CLINICAL CORRELATIONS
Intraoperative Hemorrhage
Bibliography
PRACTICE QUESTIONS
Integrated Cardiovascular Responses
KEY POINTS
Chapters 18 to 25 describe the various elements of cardio­vascular function and control.
Heart Failure Is Compensated for by Both Starling's Mechanism and the Arterial Baroreflex
Serious Complications Secondary to Heart Failure Include Exercise Intolerance, Edema, Salt and Water Retention, Uremia, Kidney Failure, Septic Shock, and Decompensation
The Immediate Cardiovascular Effects of Hemorrhage Are Minimized by Compensations Initiated by the Atrial Volume Receptor Reflex and the Arterial Baroreceptor Reflex
The Blood VoIume Lost in Hemorrhage Is Restored Through a Combination of Capillary Fluid Shifts and Hormonal and Behavioral Responses
The Initiation of Exercise Involves an Interplay of Local and Neural Changes That Increases Cardiac Output and Delivers Increased Flow to Exercising Muscle
CLINICAL CORRELATIONS
Exercise Intolerance Secondary to Congestive Heart Failure
Cow with "Hardware Disease"
Bibliography
PRACTICE QUESTIONS
Gastrointestinal Physiology and Metabolism
Regulation of Gastrointestinal Function
KEY POINTS
The gastrointestinal (GD system is regulated in an integrated manner from two control systems.
An Independent, Intrinsic Enteric Nervous System LiesWithin the Wall of the Gut
The Enteric Nervous System Contains Receptors, Sensory Neurons, Interneurons, and Motor Neurons
The Gut Receives Extrinsic Innervation from the Autonomic Nervous System
The Gut Contains Afferent Neurons That Relay Information to the Central Nervous System
The Gastrointestinal System Has an Intrinsic Endocrine System
The Immune System Participates in Regulation of Gastrointestinal Activity
The Regulation of Gastrointestinal Function Is Integrated by the Interaction of Many Regulatory Molecules on Multiple Cell Types in the Gut
Bibliography
PRACTICE QUESTIONS
Movements of the Gastrointestinal Tract
KEY POINTS
The walls of the gastrointestinal (GI) tract, at all levels, are muscular and capable of movement.
SlowWaves of Electrical Depolarization Are a Unique Feature of Gut Smooth Muscle
When Slow Waves Reach Sensitized Smooth Muscle Cells, Action Potentials and Contraction Result
Coordinated Motility Enables the Lips, Tongue, Mouth, and Pharynx to Grasp Food and Propel It down the Gastrointestinal Tract
Motility of the Esophagus Propels Food from the Pharynx to the Stomach
The Function of the Stomach Is to Process Food into a Fluid Consistency and Release It into the Intestine at a Controlled Rate
The Proximal Stomach Stores Food Awaiting Further Gastric Processing in the Distal Stomach
The Distal Stomach Grinds and Sifts Food Entering the Small Intestine
Control of Gastric Motility Differs in the Proximal and Distal Stomach
The Rate of Gastric Emptying Must Match the Small Intestine's Rate of Digestion and Absorption
Between Meals, the Stomach Is Cleared of Indigestible Material
Vomiting Is a Complex Reflex Coordinated from the Brainstem
Motility of the Small Intestine Has Digestive and Interdigestive Phases
The Ileocecal Sphincter Prevents Movement of Colon Contents Back into the Ileum
Motility of the Colon Causes Mixing, Retropulsion, and Propulsion of Ingesta
The Colon Is an Important Site of Storage and Absorption in All Animals
Despite LargeAnatomicaI Differences in the Colons of Herbivores Compared to Omnivores and Carnivores, There Are Similarities in Motility
The Anal Sphincter Has Two Layers with Separate Innervation
The Rectosphincteric Reflex Is Important in Defecation
Major Differences Between Avian and Mammalian Digestive Systems Include, in Birds, Both the Lack of Teeth and the Separation of Gastric Functions into DistinctAnatomicaI Regions
CLINICAL CORRELATIONS
Equine Rabies
Bibliography
PRACTICE QUESTIONS
Secretions of the Gastrointestinal Tract
KEY POINTS
Digestion and absorption can take place only in the aqueous milieu of digestive secretions.
THE SALIVARY GLANDS
Saliva Moistens, Lubricates, and Partially Digests Food
Salivary Secretions Originate in the Gland Acini and Are Modified in the Collecting Ducts
Salivary Glands Are Regulated by the Parasympathetic Nervous System
Ruminant Saliva Is a Bicarbonate- Phosphate Buffer Secreted in Large Quantities
GASTRIC SECRETION
Depending on the Species, There May Be Two General Types of Gastric Mucosa: Glandular and Nonglandular
The Gastric Mucosa Contains Many Different Cell Types
The Gastric Glands Secrete Hydrochloric Acid
Pepsin Is Secreted by Gastric Chief Cells in an Inactive Form and Is Subsequently Activated in the Gut Lumen
The Parietal Cells Are Stimulated to Secrete by the Action of Acetylcholine, Gastrin, and Histamine
THE PANCREAS
Pancreatic Exocrine Secretions Are Indispensable for the Digestion of the Complex Nutrients: Proteins, Starches, and Triglycerides
Acinar Cells Secrete EnzymesfWhereas Centroacinar Cells and Duct Cells Secrete a Sodium Bicarbonate Solution
Pancreatic Cells Have Cell Surface Receptors Stimulated by Acetylcholine, Cholecystokinin, and Secretin
BILE SECRETION
One function of the liver is being a secretory gland of the digestive system. Its secretion, bile, has an important role in fat digestion.
The Liver Is an Acinar Gland with Small Acinar Lumina Known as Canaliculi
Bile Contains Phospholipids and Cholesterol Maintained in Aqueous Solution by the Detergent Action of Bile Acids
The Gallbladder Stores and Concentrates Bile During the Periods Between Feeding
Bile Secretion Is Initiated by the Presence of Food in the Duodenum and Stimulated by the Return of BiIeAcids to the Liver
CLINICAL CORRELATIONS
Horse in Pain with Weight Loss
Bibliography
PRACTICE QUESTIONS
Digestion and Absorption: the Nonfermentative Processes
KEY POINTS
Digestion and Absorption Are Separate, but Related, Processes
The Small-Intestinal Mucosa Has a Large Surface Area and Epithelial Cells with "Leaky" Junctions Between Them
The Intestinal Surface Microenvironment Consists of Glycocalyx, Mucus, and an UnstirredWater Layer
DIGESTION
Breaking Down Food Particle Size by Physical Action Is an Important Part of the Digestive Process
Chemical Digestion Results in the Reduction of Complex Nutrients into Simpler Molecules
Luminal-Phase Carbohydrate Digestion Results in the Production of Short-Chain Polysaccharides
Luminal-Phase Digestion of Carbohydrates Applies Only to Starches, Because Sugars Are Digested in the Membranous Phase
Proteins Are Digested by a Variety of Luminal-Phase Enzymes
Membranous-Phase Digestive Enzymes Are a Structural Part of the Intestinal Surface Membrane
Membranous-Phase Digestion Occurs Within the Microenvironment of the Unstirred Water Layer, Intestinal Mucus, and Glycocalyx
A Specific Membranous-Phase Enzyme Exists for the Digestion of Each Type of Polysaccharide
Complete Digestion of Peptides to Free Amino Acids Takes Place Both on the Enterocyte Surface and Within the Cells
INTESTINAL ABSORPTION
Absorption refers to the movement of the products of digestion across the intestinal mucosa and into the vascular system for distribution.
Specialized Nutrient Transport Systems Exist in the Apical and Basolateral Membranes
Secondary and Tertiary Active Transport Mechanisms Utilize the Transcellular Sodium Ion Electrochemical Gradient as Their Source of Energy
Passive Transport Occurs Either Through Ion Channels in Cell Membranes or Directly Through the Tight Junctions
The Products of Membranous-Phase Digestion Are Absorbed by Sodium Co-Transport
ABSORPTION OF WATER AND ELECTROLYTES
There Are at Least Three Distinct Mechanisms of Sodium Absorption
There Are Three Major Mechanisms of Chloride Absorption
Bicarbonate Ion Is Secreted by Several Digestive Glands and Must Be Recovered from the Gut if Body Acid-Base Balance Is to Be Maintained
Potassium Is Absorbed Primarily by Passive Diffusion Through the Paracellular Route
The Major Mechanisms of Electrolyte Absorption Are Selectively Distributed Along the Gut
All IntestinaIWaterAbsorption Is Passive, Occurring Because of the Absorption of OsmoticaIIyActive Solutes
INTESTINAL SECRETION OF WATER AND ELECTROLYTES
In addition to the water and electrolytes that are secreted into the intestine by the pancreas, liver, and other glandular organs, a considerable portion of GI water and electrolyte secretion occurs directly from the intestinal surface.
Passive Increases in Luminal Osmotic Pressure Occur During Hydrolytic Digestion and Result in Water Secretion
Active Secretion of Electrolytes from the Crypt Epithelium Leads to Intestinal Water Secretion
GASTROINTESTINAL BLOOD FLOW
Water and Solute Movement Between the Lateral Spaces and Villous Capillaries Is Subject to the Same Forces That Govern Water and Solute Movement Between the Extracellular and Vascular Fluids in Other Tissues
Absorbed Nutrients Enter the Capillaries by Diffusion from the Lateral Spaces
A Countercurrent, Osmotic-Multiplier System May Increase the Osmolality of Blood at the Tips of the Villi, Further Promoting Absorption of Water into the Blood
Disturbances in the Venous Drainage from the Intestine Can Greatly Affect the Mechanisms of Capillary Absorption in the Villi
DIGESTION AND ABSORPTION OF FATS Detergent Action as Well as Enzymatic Action Is Necessary for the Digestion and Absorption of Lipids
Lipids Are Absorbed Through the Apical Membrane by Carrier Proteins and Simple Diffusion
Bile Acids Are Reabsorbed from the Ileum by a Sodium Co-Transport System
Absorbed Lipids Are Packaged into Chylomicrons Before Leaving the Enterocytes
GROWTH AND DEVELOPMENT OF THE INTESTINAL EPITHELIUM
The Length of Intestinal Villi Is Determined by the Relative Rates of Cell Loss at the Tips and Cell Replenishment at the Base
DIGESTION IN THE NEONATE
During the First Few Hours of Life, Proteins Are Not Digested but Are Absorbed Intact
The Major Intestinal Disaccharidase Switches from Lactase to Maltase with Maturity
PATHOPHYSIOLOGY OF DIARRHEA
Diarrhea refers to an increase in frequency of defecation or fecal volume.
Diarrhea OccursWhen There Is a Mismatch Between Secretion and Absorption
CLINICAL CORRELATIONS
Diarrhea with Dehydration and Acidosis in a Calf
Juvenile Pancreatic Atrophy in a Dog
Digestion: the Fermentative Processes
KEY POINTS
Fermentation Is the Metabolic Action of Bacteria
The Sites of Fermentative Digestion Must Be Conducive to Microbial Growth
MICROBIAL ECOSYSTEM OF FERMENTATIVE DIGESTION
The Microbes Responsible for Fermentative Digestion Include Bacteria, Fungi, and Protozoa
Cooperation and Interplay Among the Many Species of Microbes Give Rise to a Complex Ecosystem in the Forestomach and Hindgut
SUBSTRATES AND PRODUCTS OF FERMENTATIVE DIGESTION
Plant Cell Walls Are Important Substrates for Fermentative Digestion and Significant Nutrient Sources for Many Species
Nutrients Other Than Cell Walls Are Also Subject to Fermentative Digestion
Anaerobic Conditions in the Rumen Result in Metabolic Activities Leading to the Production of Volatile Fatty Acids
Volatile Fatty Acids Are Important Energy Substrates for the Host Animal
Fermentative Digestion of Protein Results in the Deamination of a Large Portion of Amino Acids
When Protein and Energy Availability in the Forestomach Are Well Matched, Rapid Microbial Growth and Efficient Protein Utilization Result
Microbial Protein Can Be Synthesized in the Rumen from Nonprotein Nitrogen Sources
Reticulorumen Motilityand MAINTENANCE OF THE RUMEN ENVIRONMENT
The Physiological Functions of the Reticulorumen Maintain an Environment Favorable to Fermentation Patterns That Are Beneficial to the Host
Rumen Fermentation Is Maintained by Selectively Retaining Actively Fermenting MaterialWhiIeAIIowing Unfermentable Residue to Pass on to the Abomasum
Gravity and Reticulorumen Motility Combine to Create the Selective Flow of Particulate Matter out of the Rumen
Functional Specific Gravity Determines the Rateat Which Particulate Matter (Solids) Moves Through the Zones of the Reticulorumen
Digestibility and Physical Characteristics of Feed Have Important Influences on Both the Rate of Particle Passage from the Rumen and the Rate of Feed Intake
Rumination, or Cud Chewing, Has an Important Effect on the Reduction of Particle Size and the Movement of Solid Material Through the Rumen
Water Moves Through the Rumen at a Much Faster Rate Than Particulate Matter
Rumen Dilution Rate Has Important Influences on Fermentation and Microbial CeIIYieId
control of Reticulorumen motility
Reticulorumen Motility Is Controlled by the Central Nervous System and Affected by Intraluminal Conditions
OMASAL FUNCTION
Passage of Material from the Reticulum to the Omasum Occurs During Reticular Contraction
VOLATILE FATTY ACID ABSORPTION
Volatile Fatty Acids, Representing 60% to 80% of the Energy Needs of the Animal, Are Absorbed Directly from the Forestomach Epithelium
rumen Developmentand ESOPHAGEAL GROOVE FUNCTION
Significant Changes in Forestomach Size and Function Occur with Dietary Changes in Early Life
The Esophageal Groove Diverts the Flow of Ingested Milk Past the Forestomach and into the Abomasum
FUNCTION OF THE EQUINE LARGE HINDGUT
The Equine Hindgut Has a Great Capacity for Fermentation
The Types of Substrate and Fermentation Patterns Are Essentially Identical for Forestomach and Hindgut Fermentation
The Motility Functions of the Cecum and Colon Retain Material for Fermentation and Separate Particles by Size
The Rate of Fermentation and Volatile Fatty-Acid Production in the Equine Colon Is Similar to That in the Rumen
Hindgut Anatomy and Function Vary Greatly Among the Many Species of Veterinary Interest
CLINICAL CORRELATIONS
Grain Engorgement Toxemia
Impaction Colic
Bibliography
PRACTICE QUESTIONS
Postabsorptive Nutrient Utilization
KEY POINTS
The rate of absorption of nutrients from the gut is not constant, but rather fluctuates greatly with food intake.
Homeostatic Mechanisms Balance the Supply and Demand OfAImostAII Nutrients
THE FURNACE
The Tricarboxylic Acid (or Krebs) Cycle Is the Major Energy-Yielding Pathway of Fuel Utilization in the Body
THE FUELS
The Major Metabolic Fuels Consist of Glucose, Amino Acids, Fatty Acids, and Ketone Bodies; Various Storage and Transport Forms Exist for These Compounds
Glucose Is the Central Fuel in the Energy Metabolism of Most Animals
Fatty Acids Are the Major Form of Energy Storage in the Animal Body
Ketone BodiesAre Fat-Derived, Water- Soluble Metabolites That Serve as Glucose Substitutes
AminoAcidsAre Important Fuels in Addition to Being the Building Blocks of Protein
NUTRIENT UTILIZATION DURING THE ABSORPTIVE PHASE
As absorption takes place, metabolic events in the liver and peripheral organs are coordinated to direct nutrients into storage molecules and storage sites. Figure 32-3 illustrates the general scheme of metabolism during the absorptive phase.
During the Absorptive Phase, the Liver Takes up Glucose and Converts It into Glycogen and Triglyceride
The Conversion of Glucose to Fatty Acids Is an Irreversible Process
Transport of Fatty Acids out of the Liver Is Through Chylomicron-Like Particles Known as Very-Low-Density Lipoproteins
Amino Acids Can Be Classified into Groups on the Basis of Metabolic Characteristics
Amino Acids Are Extensively Modified During Absorption
Many Amino Acids Are Removed by the Liver on "First Pass," Never Reaching the Systemic Circulation
Some Amino Acids Taken up by the Liver Are Used for Protein Synthesis
Most Amino Acids Taken up by the Liver Are Converted to Carbohydrates
Not All Amino Acids Are Subject to Hepatic Destruction
Metabolism at the Tissue Level Is Coordinated with Hepatic Metabolism and Results in the Deposition of Fuel into Storage Tissues During the Absorptive Period
Insulin Promotes the Synthesis of Protein and the Deposition of Glycogen in Muscle
Insulin-Stimulated Uptake of Amino Acids by Muscle Results in a Net Increase in Muscle Protein Synthesis
During the Absorptive Phase, Triglyceride Accumulation in Adipose Tissue Occurs by Two Mechanisms: Uptake from Very-Low-Density Lipoproteins and Direct Lipid Synthesis from Glucose
NUTRIENT UTILIZATION DURING THE Postabsorptive phase
The postabsorptive phase is the relatively brief period (usually a few hours) between meals in well-fed animals.
Hepatic Metabolism Switches from Glucose Utilization to Glucose Production During the Postabsorptive Phase
Fuel Mobilization in Peripheral Tissues Occurs when the Blood Insulin Concentration Declines
Muscle Reacts to a Metabolic Demand for Glucose by Mobilizing Amino Acids to Support Hepatic Gluconeogenesis
Muscle Release of Amino Acids Is Related to Reduced Glucose and Amino Acid Uptake
The Complex Pattern of Muscle Amino Acid Catabolism and Release Is Necessary to Accommodate the Liver's Limited Capacity for Uptake of Branch-Chain Amino Acids and to Facilitate the Removal of Amino Nitrogen from the Muscle
The Reaction OfAdipose Tissue During the Postabsorptive Phase Is to Mobilize Fatty Acids
NUTRIENT UTILIZATION DURING PROLONGED ENERGY MALNUTRITION OR COMPLETE FOOD DEPRIVATION
During Prolonged Periods of Fasting or Undernutrition, Glucose and Amino Acids Are Conserved by Extensive Utilization of Fats and Ketone Bodies for Energy Production
A Large Portion of the Fatty Acids Released from Adipose Tissue Is Taken up Directly by the Liver
Hepatic Ketone Body Formation Is Promoted by Low Glucose Availability, a High Glucagon/lnsulin Ratio, and a Ready Supply of Fatty Acids
Glucagon Plays an Important Role in the Excessive Production of Ketone Bodies in Diabetes Mellitus
Fatty Acids Cannot Be Used for Glucose Synthesis
Hormonal Conditions Direct the Distribution of Very-Low-Density Lipoprotein Fatty Acids in the Body
Ketone Bodies Are Formed in the Mitochondria from Acetyl Coenzyme A
Hepatic Very-Low-Density Lipoproteins May Be Synthesized from Adipose-Derived Fatty Acid as Well as from Newly Synthesized Fatty Acid
Changes in Growth Hormone Concentrations May Aid in Shifting Peripheral Fuel Utilization from Glucose and Amino Acids to Ketone Bodies and Fatty Acids
SPECIAL FUEL CONSIDERATIONS OF RUMINANTS
Ruminants Exist in a Perpetual State of Gluconeogenesis Because of Their Unique Digestive Process
Hepatic Lipidosis in a Cat
Bibliography
PRACTICE QUESTIONS
Endocrinology
Deborahs. Qreco,
Qeorqe H. Staberfelhtt
The Endocrine System
KEY POINTS
GENERAL CONCEPTS
Hormones Are Chemicals Produced by SpecificTissuesThat AreTransported by the Vascular System to Affect Other Tissues at Low Concentrations
The Endocrine and Nervous Systems Are Integrated in Their Control of Physiological Processes
SYNTHESIS OF HORMONES
Protein Hormones Are Initially Synthesized as Preprohormones and Then Cleaved in the Rough Endoplasmic Reticulum to Form Prohormones and in the Golgi Apparatus to Form the Active HormonesfWhich Are Stored in Granules Before Being Released by Exocytosis
Steroids Are Synthesized from ChoIesteroLWhich Is Synthesized by the Liver; Steroids Are Not Stored but Are Released as They Are Synthesized
TRANSPORT OF HORMONES IN THE BLOOD
Protein HormonesAre Hydrophilic and Carried in the Plasma in Dissolved Form
Steroids and Thyroid Hormones Are Lipophilic and Carried in Plasma in Association with Both Specific and Nonspecific Binding Proteins; the Amount of Unbound, Active Hormone Is Relatively Small
HORMONE-CELL INTERACTION
Protein Hormones Have Specific Receptors on Target Tissue Plasma MembranesrWhereas Steroids Have Specific ReceptorsWithin the Cytoplasm or Nucleus
POSTRECEPTOR CELL RESPONSES
Steroids Interact Directly with the Cell Nucleus Through the Formation of a Complex with Its Cytosolic Receptor, Whereas Protein Hormones Need a Messenger Because They Cannot Enter the Cell
METABOLISM OF HORMONES
Steroid Hormones Are Metabolized by Conjugation with Sulfates and GlucuronidesrWhich Makes Steroids Water Soluble
FEEDBACK CONTROL MECHANISMS
The Most Important Feedback Control for Hormones Is the Negative-Feedback System, in Which Increased Hormone Concentrations Result in Less Production of the Hormone, Usually Through an Interaction with the Hypothalamus or Pituitary Gland
Endocrine Secretory Patterns Can Be Influenced by Factors Such as Sleep or Light and Can Produce Circadian Rhythms
THE HYPOTHALAMUS
The Hypothalamus Coordinates the Activity of the Pituitary Gland Through the Secretion of Peptides and Amines
THE PITUITARY GLAND
The pituitary gland, or hypophysis cerebri, is composed of the adenohypophysis (pars distalis, or anterior lobe), the neurohypophysis (pars nervosa, or posterior lobe), the pars intermedia (intermediate lobe), and the pars tuberalis (Figure 33-10).
The Neurohypophysis Has Cell Bodies That Originate in the Hypothalamus, with Cell Endings That Secrete Oxytocin and Vasopressin
Oxytocin and Vasopressin Are Synthesized in Cell BodiesWithin the Hypothalamus and Are Carried by Axon Flow to the Posterior Lobe, Where They Are Released
The Main Effects of Oxytocin Are on the Contraction of Smooth Muscle (Mammary Gland and Uterus); the Effects OfVasopressin Are Primarily on the Conservation of Water (Antidiuresis) and Secondarily on Blood Pressure
Plasma Osmolality Controls the Secretion of Vasopressin
Adenohypophyseal Activity Is Controlled by Hypothalamic Releasing Hormones, Which Are Released into the Portal SystemzWhich in Turn Connects the Median Eminence of the Hypothalamus and the Anterior Pituitary Gland
CLINICAL CORRELATIONS
Equine Cushing's Disease
Bibliography
PRACTICE QUESTIONS
Endocrine Glands and Their Function
KEY POINTS
THE THYROID GLAND
The Thyroid Hormones Are Synthesized from Two Connected Tyrosine Molecules That Contain Three or Four Iodine Molecules
Thyroid Hormones Are Stored Outside the Cell and Attached to Thyroglobulin in the Form of Colloid
The Release of Thyroid Hormones Involves Transport of Thyroglobulin with Attached Thyroid Hormones into the Cell, Cleavage of the Thyroid Hormones from Thyroxine-Binding Globulin, and Release into the Interstitial Tissues
Thyroid Hormones Are Transported in the Plasma Attached to Plasma Proteins
The Main Routes of Metabolism of Thyroid Hormones Are Through Deiodination or the Formation of Glucuronides and Sulfates via Hepatic Mechanisms
Thyroid Hormones Are the Primary Factors for the Control of Basal Metabolism
The Ingestion of Compounds That Inhibit the Uptake or Organic Binding of Iodine Blocks the Thyroid's Ability to Secrete Thyroid Hormones and Causes Goiter
The adrenal glands
The Adrenal Glands Are Composed of Two Organs: the Outer Gland (Cortex) and the Inner Gland (Medulla)
THE ADRENAL CORTEX
The Adrenal Cortex Has Three Zones: the Zona GlomeruIosafWhich Secretes Mineralocorticoids, and the Zona Fasciculata and the Zona Reticularis, Which Secrete Glucocorticoids and Sex Steroids
Adrenal Corticoids Are Synthesized from Cholesterol; the Critical Difference in the Activity of These Corticoids Is Related to the Hydroxyl Group on C-17 of Glucocorticoids
Adrenocortical Hormones Are Carried in Plasma in Association with Specific Binding Globulins (Corticosteroid- Binding Globulin)
The Metabolism of Adrenocortical Hormones Involves the Reduction of Double Bonds and Conjugation of the Steroids to Glucuronides and Sulfates
One of the Most Important Functions of Glucocorticoids Is Control of Metabolism, in Particular the Stimulation of Hepatic Gluconeogenesis
Corticotropin Is the Pituitary Hormone That Regulates Glucocorticoid Synthesis by the Adrenal Cortex
One of the Most Important Clinical Uses of Glucocorticoids Is the Suppression of the Inflammatory Response
The Main Factors That Stimulate Catecholamine Secretion Are Hypoglycemia and Conditions That Produce Stress
HORMONES OF THE PANCREAS
The pancreas has important endocrine and nonendocrine functions. The nonendocrine functions result from activity of the exocrine part of the pancreas and are involved in GI function.
CALCIUM AND PHOSPHATE METABOLISM
Calcium Is Important for Intracellular Reactions, Including Muscle Contraction, Nerve Cell Activity, Release of Hormones Through Exocytosis, and Activation of Enzymes
Phosphate Is Important for the Structure of Bone and Teeth, and Organic Phosphate Serves as Part of the Cell Membrane and Several Intracellular Components
The Most Important Body Pool of Calcium Involved in Homeostasis Is the Extracellular Fluid Component
CLINICAL CORRELATIONS
Diabetes Mellitus
Bibliography
PRACTICE QUESTIONS
Reproduction and Lactation
Autuwub P. VamMokb * Qeorqe H. Staheκfeldtt
Control of Gonadal and Gamete Development
KEY POINTS
DEVELOPMENT OFTHE REPRODUCTIVE SYSTEM
Organization of the Gonads Is Under Genetic Control
Sexual Organization of the Genitalia and Brain Depends on the Presence or Absence of Testosterone
Hypothalamopituitary control of REPRODUCTION
The Hypothalamus and Anterior Pituitary (Adenohypophysis) Secrete Protein and Peptide HormonesrWhich Control Gonadal Activity
The Adenohypophysis (Pars Distalis) Produces Follicle-Stimulating Hormone, Luteinizing Hormone, and ProIactinrAII OfWhich Control Reproductive Processes
MODIFICATION OF GONADOTROPIN RELEASE
OVARIAN FOLLICLE DEVELOPMENT
Gamete Development Occurs Initially Without Gonadotropin Support and Subsequently with Pulsatile Gonadotropin Secretion
In the Preantral Follicle, Gonadotropin Receptors for Luteinizing Hormone Develop on the ThecarWhich Results in Androgen Synthesis; Follicle-Stimulating Hormone Directs the Granulosa to Transform the Androgens to Estrogens
Late in the Ovarian Follicular Phase, Luteinizing Hormone Receptors Develop on the GranuIosazWhich Permits the Preovulatory Surge of Luteinizing Hormone to Cause Ovulation
CLINICAL CORRELATIONS
Androgen Insensitivity
Bibliography
PRACTICE QUESTIONS
Control of Ovulation and the Corpus Luteum
KEY POINTS
OVULATION
Ovulatory Follicles Are Selected at the Onset of Luteolysis (Large Domestic Animals)
Ovulation Is Caused by an Estrogen- Induced Preovulatory Surge of Gonadotropins
CORPUS LUTEUM
The Corpus Luteum Secretes Progesterone, Which Is Essential for Pregnancy
Luteinizing Hormone Is Important for the Maintenance of the Corpus Luteum
Regression of the Corpus Luteum in Nonpregnant Large Domestic Animals Is Controlled by Uterine Secretion of Prostaglandin F2α
Changes in Luteal Life Span in Large DomesticAnimaIs Occur Because of Changes in Prostaglandin F2α Synthesis by the Uterus
OVARIAN CYCLES
In Spontaneously Ovulating Animals, Ovarian Cycles Have Two Phases: Follicular and Luteal; Animals That Require Copulation for Ovulation Can Have Only a Follicular Phase
The Luteal Phase Is Modified by Copulation in Some Species
CLINICAL CORRELATIONS
Inability to Impregnate a Mare
Persistent Luteal Phase in the Mare
Bibliography
PRACTICE QUESTIONS
Reproductive Cycles
KEY POINTS
REPRODUCTIVE CYCLES
The Two Types of Reproductive Cycles Are Estrous and Menstrual
PUBERTY AND REPRODUCTIVE SENESCENCE
Puberty Is the Time at Which Animals First Release Mature Germ Cells
Reproductive Senescence in Primates Occurs Because of Ovarian Inadequacy, Not Inadequacy of Gonadotropin Secretion
SEXUAL BEHAVIOR
Sexual Receptivity Is Keyed by the Hormones Estrogen and Gonadotropin-Releasing Hormone in the Female and Testosterone in the Male
EXTERNAL FACTORS CONTROLLING REPRODUCTIVE CYCLES
Photoperiod, Lactation, Nutrition, and Animal Interaction Are Important Factors That Affect Reproduction
Inadequate Nutrition Results in Ovarian Inactivity, Especially in Cattle
CLINICAL CORRELATIONS
Sexual Attractiveness in the Spayed Bitch
Bibliography
PRACTICE QUESTIONS
Pregnancy and Parturition
KEY POINTS
PREGNANCY
The Development of an Embryo Involves Fusion of an Oocyte and Spermatozoon Within the Oviduct
Extension of the Life Span of the Corpus Luteum in Large Domestic Species and Cats Is Essential for Pregnancy Maintenance
The Placenta Acts as an Endocrine Organ
PARTURITION
Fetal Cortisol Initiates Delivery Through Increased Secretion of Estrogen and Thus Prostaglandin F2α
CLINICAL CORRELATIONS
Prolonged Gestation
Bibliography
PRACTICE QUESTIONS
The Mammary Gland
KEY POINTS
Animals that belong to the class Mammalia are charac­terized as having bodies that are basically covered with hair, delivering live young instead of eggs (the mono* tremes are an exception), and, pertinent to this chapter, nurtur­ing their young through the use of structures called mammary glands.
Anatomicalaspects of the MAMMARY GLAND
The Milk-Secreting Cells of the Mammary Gland Develop Through the Proliferation of Epithelium into Hollow Structures Called Alveoli
Most of the Milk ThatAccumuIates Before Suckling or Milking Is Stored in the Alveoli, Even ThoughAnimaIs Have Enlarged Milk-Storage Areas Called Cisterns
A Suspensory System Involving the Udder of the Cow Allows the Animal to Carry a Large Amount of Milk
control of Mammogenesis
Initial Development of the Mammary Gland Is Programmed by Embryonic Mesenchyme
Proliferation of the Mammary Duct System Begins at Puberty, with Ducts Under the Control of Estrogens, Growth Hormone, and Adrenal Steroids, and Alveoli Under the Control of Progesterone and Prolactin
COLOSTRUM
Prepartum Milk Secretion (Without Removal) Results in the Formation of Colostrum
The Ingestion of Colostrum Is Important Because of the Passive Immunity It Confers Through the Presence of High Concentrations of Immunoglobulins
The Time Immunoglobulins Can Be Absorbed Through the Gut Is Limited to the First 24 to 36 Hours of Life
Lipids (ParticuIarIyVitamin A) and Proteins (Caseins and Albumins) Are High in Concentration in Colostrum; Carbohydrates (Lactose) Are Low
LACTOGENESIS
Prolactin, Inhibited by Dopamine and Stimulated by Vasoactive Intestinal Peptide, Is the Most Important Hormone Involved in the Process of Milk Synthesis, or Lactogenesis; Growth Hormone Is Also Important for Lactogenesis
The Release of Fat into Milk from the Alveolar Cell Involves Constriction of the Plasma Membrane Around the Fat Droplet; Fats Are Dispersed in Milk in Droplet Form
Milk Proteins and Lactose Are Released from Alveolar Cells by the Process of Exocytosis
MILK REMOVAL
In order for lactogenesis to be maintained, milk must be removed from the mammary gland by suckling or milking.
Efficient Milk Removal Requires the Release of OxytocinrWhich Causes Contraction of Muscle Cells That Surround the Alveoli (Myoepithelial Cells), and Movement of Milk into the Ducts and Cisterns
FIRST NURSING
Carbohydrate Stores Are Good in Neonates Bom as Singles or Twins, Whereas Carbohydrate Stores Are Low in Neonates Bom in Litters; the Former Can Stand a Longer Interval to First Suckling Than Can the Latter
COMPOSITION OF MILK
Fats Are the Most Important Energy Source in Milk
Lactose, Composed of Glucose and Galactose, Is the Main Carbohydrate of Mammalian Milk
The Main Proteins in Milk Are Called Caseins and Are Found in Curd
THE LACTATION CYCLE
The time required for changeover from colostrum to normal milk secretion varies with each species.
Milk Production Peaks at 1 Month Postpartum in Dairy Cattle, Followed by a Slow Decline in Production; Milking Usually Stops at 305 Days of Lactation So That the Animal Can Prepare the Mammary Gland for the Next Lactation
Lactation Can Be Induced by Hormone Administration (Estrogen and Progesterone) and Enhanced by Growth Hormone and Increased Photoperiod Exposure
Diseasesassociatedwith the MAMMARY GLAND
The Main Diseases That Affect the Mammary Gland Directly Are Mastitis (Prevalent in Dairy Cattle and Dogs) and Neoplasia (Prevalent in Intact Dogs and Cats)
The Main Conditions That Involve the Mammary Gland Indirectly Are Passive Transfer of Red Blood Cell Agglutinating Antibodies by the Ingestion of Colostrum (Mare) and Hypocalcemia Caused by the Transient Drain of Calcium That Occurs with Initiation of Lactation (Dairy Cattle) or During the Perinatal Period (Dog)
CLINICAL CORRELATIONS
Pregnant Mare That Does Not Have Sufficient Milk or Udder Development
Neonatal Isoerythrolysis
Bibliography
PRACTICE QUESTIONS
Reproductive Physiology of the Male
KEY POINTS
FUNCTIONAL ANATOMY
Emission Is the Release of Spermatozoa and Accessory Gland Fluids into the Pelvic Urethra, Whereas Ejaculation Is the Forceful Expulsion of Semen from the Urethra
SPERMATOGENESIS
Spermatogenesis Is a Lengthy Orchestrated Process in Which Diploid Stem Cells Divide by Mitosis to Maintain Their Own Numbers and Cyclically Produce Progeny That Undergo Meiotic Division and Differentiation into Haploid Germ Cells
HYPOTHALAMIC-PITUITARY-TESTICULAR AXIS
The Reproductive System of the Male Is Regulated by the HypothaIamusrWhich Is Hormonally Linked to the Anterior Pituitary and Testes by Luteinizing Hormone and Follicle-Stimulating Hormone
PUBERTY
Puberty Is Not Synonymous with Sexual Maturity
Puberty Results from a Continuous Process of Endocrine Changes ThatAre Initiated Shortly After Birth
ANABOLIC STEROIDS
Anabolic Steroids Are Androgen Derivatives That Exert Negative Feedback on the Hypothalamic-Pituitary-TesticuIarAxis
CLINICAL CORRELATIONS
Infertility in a Stallion
Bibliography
PRACTICE QUESTIONS______
Renal Physiology
Glomerular Filtration
KEY POINTS
Introduction to the Physiology of the Kidney
The Glomerulus Filters the Blood
The Structure of the Glomerulus Allows Efficient, Selective Filtration
Glomerular Filtration Rate Is Determined by the Mean Net Filtration Pressure, Permeability of the Filtration Barrier, and Area Available For Filtration
Glomerular Filtration Rate Is Regulated by Systemic and Intrinsic Factors
Glomerular Filtration Rate Is Measured by Determining Plasma Clearance Rate of a Substance
CLINICAL CORRELATIONS
Chronic Renal Failure
Glomerulonephritis
Bibliography
PRACTICE QUESTIONS
Solute Reabsorption
KEY POINTS
The Renal Tubule Reabsorbs Filtered Substances
Renal Tubule Function May Be Assessed by Determining Fractional Excretion and Fractional Reabsorption Rates
The Proximal Tubule Reabsorbs the Bulk of Filtered Solutes
The Proximal Tubule Secretes Organic Ions
The Distal Tubule Segments Reabsorb Salts and Dilute the Tubule Fluid
The Collecting Duct Reabsorbs Sodium Chloride and Can Secrete or Reabsorb Potassium
The Distal Tubule and Collecting Duct Respond to Systemic Signals to Alter Salt Excretion as Required
Aldosterone Enhances Sodium Reabsorption and Potassium Secretion
Other Hormones Regulate Sodium Transport, Including Angiotensin II, Antidiuretic Hormone, Endothelin, and Atrial Natriuretic Peptide
Calcium Is Reabsorbed in the Distal Nephron and Connecting Segment, Regulated by Parathyroid Hormone, Vitamin D3, and Calcitonin
CLINICAL CORRELATIONS
Glucosuria
Hypoadrenocorticism
Bibliography
PRACTICE QUESTIONS
Water Balance
The Kidney MaintainsWater Balance
The ProximaITubuIe Reabsorbs More Than 60% of Filtered Water
The Kidney Can Produce Either Concentrated or Diluted Urine
A Hypertonic Medullary Interstitium Is Needed to Form Concentrated Urine
The Juxtamedullary Nephrons Extend Deep into the Inner Medulla
Solute Reabsorption by the Medullary ThickAscending Limb and Collecting Duct Generates and Maintains Medullary Hypertonicity
The Countercurrent Mechanism Increases Medullary Interstitial Osmolality with Minimal Energy Expenditure
Countercurrent Exchange in the Vasa Recta Removes Water from the Medullary Interstitium Without Reducing Medullary Interstitial Hypertonicity
Active Sodium Chloride Reabsorption in IheThickAscending Limb and the Distal ConvoIutedTubuIe Dilutes the Tubule Fluid
Antidiuretic Hormone Regulates Collecting DuctWater Permeability to Determine the Final Urine Osmolality
Cells in the Inner Medulla Adapt to Interstitial Hyperosmolality by Accumulation of Organic Osmolytes
CLINICAL CORRELATIONS
Diabetes Insipidus
Chronic Renal Insufficiency
Bibliography
PRACTICE QUESTIONS
Acid-Base Balance
KEY POINTS
Buffers, Lungs, and Kidneys Together Maintain Acid-Base Balance
The Kidneys Generate New Bicarbonate and Excrete Ammonium Ion
The Collecting Duct Determines the Final Urine pH
The Proximal Tubule Has a High Capacity for H* Secretion and Bicarbonate Reabsorption
The Collecting Duct Can Secrete Protons and Generate Acidic Urine
The Collecting Duct Can Secrete Bicarbonate and Generate Alkaline Urine
CLINICAL CORRELATIONS
Respiratory Acidosis with Renal Compensation
Metabolic Alkalosis with Paradoxical Aciduria
Bibliography
PRACTICE QUESTIONS
Respiratory Function
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Overview of Respiratory Function: Ventilation of the Lung
KEY POINTS
RESPIRATORY FUNCTION
The Respiratory System's Primary Function Is the Transport of Oxygen and Carbon Dioxide Between the Environment and the Tissues
VENTILATION
Ventilation Is the Movement of Gas into and out of the Lung
Ventilation Requires Muscular Energy
The Lung Is Mechanically Connected to the Thoracic Cage by the Pleural Liquid
Airflow Is Opposed by Frictional Resistance in the Airways
Smooth Muscle Contraction Affects the Diameters of the Trachea, Bronchi, and Bronchioles
Dynamic Compression Can Narrow the Airways and Limit Airflow
The Distribution of Air Depends on the Local Mechanical Properties of the Lung
In Some Species, Air Travels Between Adjacent Regions of Lung Through Collateral Pathways
CLINICAL CORRELATIONS
Lung Fibrosis in the Dog
Chronic Airway Disease in the Horse
Bibliography
PRACTICE QUESTIONS
Pulmonary Blood Flow
KEY POINTS
Bronchial Circulation
PULMONARY CIRCULATION
The pulmonary circulation differs from the systemic circula­tion in that all the blood passes through only one organ: the lung.
The Structure of the Pulmonary Arteries Varies Among Species
Functionally, Pulmonary Blood Vessels Can Be Classified as Alveolar and Extra-Alveolar Vessels
The Pulmonary Blood VesselsOffer a Low Resistance to Flow
The Distribution of Pulmonary Blood FIowWithin the Lung Is Influenced by Several Factors
Passive Changes in Vascular Resistance Result from Changes in Vascular Transmural Pressure
Neural and Humoral Factors Cause Contraction of the Muscular Pulmonary Arteries
Alveolar Hypoxia Is a Potent Constrictor of Small Puimonary Arteries
During Exercise the Pulmonary Circulation Must Accommodate a Large Increase in Blood Flow
BRONCHIAL CIRCULATION
The Bronchial Circulation Provides a Blood Supply to Airways, Large Vessels, and in Some Species the Visceral Pleura
Clinical correlations
Brisket Disease in a Heifer
Bibliography
PRACTICE QUESTIONS
Gas Exchange
KEY POINTS
The Composition of a Gas Mixture Can Be Described by the Fractional Composition or Partial Pressure
Alveolar Gas Composition Is Determined by AlveoIarVentiIation and the Exchange of Oxygen and Carbon Dioxide
Exchange of Oxygen and Carbon Dioxide Between the Alveolus and Pulmonary Capillary Blood Occurs by Diffusion
The Exchange of Gases Between the Tissues and Blood Also Occurs by Diffusion
The Amount Of AlveoIarVentiIation in Relation to Pulmonary Capillary Blood Flow—the V/QRatio—Determines the Adequacy of Pulmonary Gas Exchange
The Composition of the Systemic Arterial Blood Is Determined by the Composition of the Capillary Blood That Drains Each Alveolus
Part of Each Breath Ventilates Dead-Space and Does Not Participate in Gas Exchange
Arterial Oxygen (Pao2) and Carbon Dioxide (Paco2) Tensions Are Measured to Evaluate Gas Exchange
CLINICAL CORRELATIONS
Hypoventilation in a Bulldog
Hypoxemia in an Anesthetized Clydesdale Horse
Bibliography
PRACTICE QUESTIONS______
Gas Transport in the Blood
KEY POINTS
OXYGEN TRANSPORT
A Small Amount of Oxygen Is Transported in Solution in Plasma, but Most Is in Combination with Hemoglobin
A Molecule of Hemoglobin Can Reversibly Combine with Four Molecules of Oxygen
The Binding of Oxygen and Hemoglobin Is Determined by Oxygen Tension
The Oxyhemoglobin Dissociation Curve Can Be Displayed with Percent Saturation of Hemoglobin as a Function of Oxygen Tension
The Affinity of Hemoglobin for Oxygen Varies with Blood Temperature, pH, Carbon Dioxide Tension, and the Intracellular Concentration of Certain Organic Phosphates
As Hemoglobin Is Depleted of Oxygen, Its Color Changes from Bright Red to Bluish Red
Carbon Monoxide Has 200 Times the Affinity of Oxygen for Hemoglobin
Methemoglobinemia Occurs in Certain Toxic States, Notably Nitrite Poisoning
CARBON DIOXIDE TRANSPORT
Carbon Dioxide Is Transported in the Blood Both in Solution in Plasma and in Chemical Combination
GAS TRANSPORT DURING EXERCISE
Oxygen Demands of ExerciseAre Met by Increases in Blood Flow, in Hemoglobin Levels, and in Oxygen Extraction from Blood
Flea Infestation in a Cat
Atrial Fibrillation in a Horse
Bibliography
PRACTICE QUESTIONS
Control Of Ventilation
KEY POINTS
Respiration Is Regulated to Meet the Metabolic Demands for Delivery of Oxygen and Removal of Carbon Dioxide
CENTRAL CONTROL OF RESPIRATION
Respiratory Rhythmicity Originates in the Medulla and Is Modified by Higher Brain Centers and Inputs from Peripheral Receptors
PULMONARY AND AIRWAY RECEPTORS
Pulmonary Stretch Receptors, Irritant Receptors, and Juxtacapillary Receptors Can Influence the Rhythm of Breathing
Muscle Spindie Stretch Receptors Monitor the Effort Exerted by Respiratory Muscles
CHEMORECEPTORS
HypoxiarAcidosis, and Hypercapnia Are All Potent Stimuli for Ventilation
Peripheral Chemoreceptors Are the Only Receptors Monitoring Blood Oxygen Levels
The Ventilatory Response to Carbon Dioxide Is Mediated Through a Medullary Chemoreceptor
Ascent to High Altitude Is Accompanied by a Decrease in Inspired Oxygen Tension and Consequently by HypoxemiarWhich Leads to an Increase in Ventilation
During ExerciserVentiIation Must Increase Because the Tissues Demand More Oxygen and Produce More Carbon Dioxide
CLINICAL CORRELATIONS
Hypoxemia with Hyperventilation in an 8-Month-0ld Samoyed
Hypoventilation in an Anesthetized Saint Bernard
Bibliography
PRACTICE QUESTIONS______
Nonrespiratory Functions of the Lung
KEY POINTS
DEFENSE MECHANISMS OFTHE RESPIRATORY SYSTEM
The Extensive, Delicate Gas Exchange Surface of an Animal's Lung Is Protected by a Variety of Specific and Nonspecific Defense Mechanisms
Particle Deposition onto the Mucociliary System Depends on Particle Size and Occurs by Impaction, Sedimentation, and Diffusion
The Respiratory Tract Is Lined by a Mucociliary Blanket Consisting of a Ciliated Epithelium Overlaid with a Layer of Mucus
Alveolar Macrophages Scavenge Particles Deposited on the Alveolar Surface
Cytokines and Chemokines Coordinate the Defense Mechanisms of the Lung
PULMONARY FLUID EXCHANGE
The Lung Continuously Produces Lymph as a Result of the Net Fluid Movement from the Pulmonary Microvasculature into the Pulmonary Interstitium
The SmaIIVoIume of Pleural Fluid Originates by Filtration from Capillaries in the Visceral and Parietal Pleura
METABOLIC FUNCTIONS OF THE LUNG
The Lung Removes Many Hormones and Toxins from the Blood and Inactivates Many Others
CLINICAL CORRELATIONS
Pleuritis in a Thoroughbred Horse
Mitral Insufficiency in a Dog
Bibliography
PRACTICE QUESTIONS
Homeostasis
Fetal and Neonatal Oxygen Transport
KEY POINTS
The Fetus Depends on the Placenta for Exchange of Gas, Nutrients, and Metabolic Byproducts
The Efficiency of Gas Exchange at the Placenta Depends on the Species- Variable Arrangement of Fetal and Maternal Blood Vessels
The Fetal Circulation Mixes Oxygenated and Deoxygenated Blood at Several Points, So the Fetus Exists in a State of Hypoxemia
Fetal Oxygen Transport Is Assisted by Fetal HemogIobinrWhich Has a High Affinity for Oxygen
The Lung Develops in Three Stages, and Pulmonary Surfactant Must Be Present at Birth
At or Shortly after Birth, Umbilical Vessels Rupture, PulmonaryVascuIar Resistance Decreases, and the Foramen Ovale and Ductus Arteriosus Close
CLINICAL CORRELATIONS
Patent Ductus Arteriosus in a Pomeranian
Bibliography
PRACTICE QUESTIONS
Acid-Base Homeostasis
KEY POINTS
ACID-BASE REGULATION
Relative Constancy of the Body's pH Is Essential Because Metabolism Requires Enzymes That Operate at an Optimal pH
Hydrogen Ion Concentration Is Measured as pH
An Acid Can Donate a Hydrogen Ion, and a Base Can Accept a Hydrogen Ion
Buffers Are Combinations of Salts and Weak Acids That Prevent Major Changes in pH
Hemoglobin and Bicarbonate Are the Most Important Blood Buffers
The First Defense against a Change in Blood pH Is Provided by the Blood Buffers, but the Lungs and Kidneys Must Ultimately Correct the Hydrogen Ion Load
Changes in Ventilation Can Rapidly Change Carbon Dioxide Tension and Therefore Alter pH
Metabolic Production of Fixed Acids Requires That the Kidneys Eliminate Hydrogen Ions and Conserve Bicarbonate
Intracellular pH Is Regulated by Buffers and Ion Pumps
ACID-BASE DISTURBANCES
Acid-Base Abnormalities Accompany Many Diseases, and Restoration of Normal Blood pH Should Be a Consideration in the Treatment of Any Disease
Respiratory Acidosis Is Caused by the Accumulation of Carbon DioxiderWhich Decreases Blood pH
RespiratoryAlkalosis Is Caused by the Loss of Carbon DioxiderWhich Increases Blood pH
Metabolic Acidosis Is Caused by the Accumulation of Fixed Acids or the Loss of Buffer BaserWhich Decreases Blood pH
Metabolic Alkalosis Is Caused by the Excessive Elimination of Hydrogen Ions or by the Intake of Base, Such as BicarbonatefWhich Increases Blood pH
Respiratory Compensations for Acid-Base Abnormalities Occur Rapidly; Renal Compensations Occur over Several Hours
Hydrogen and Potassium Ions Are Interrelated in Acid-Base Homeostasis
The Diagnosis of Acid-Base Disturbances Depends on Interpretation of Measurements of Arterial Blood pH and Carbon Dioxide Tension, from Which Bicarbonate Concentration and Total Buffer Base Are Calculated
CLINICAL CORRELATIONS
UpperAirway Obstruction in a Boston Terrier
Bibliography
PRACTICE QUESTIONS
Thermoregulation
KEY POINTS
Temperature Is a Major FactorAffecting Tissue Function
Homeotherms and Poikilotherms Use Different Strategies to Regulate Body Temperature
Body Temperature Depends on the Balance Between Heat Input and Heat Output
HEAT PRODUCTION
Heat is a Byproduct of All Metabolic Processes
Shivering Produces Heat by Muscle Contraction
Nonshivering Thermogenesis Is an Increase in Basal Metabolic Rate, Caused Especially by the Oxidation of Fats, to Produce Heat
HEAT TRANSFER IN THE BODY
Because Tissues Are Poor Conductors, Heat Is Most Effectively Transferred in the Blood
Countercurrent Heat Exchange Mechanisms Are Used Both to Conserve and to Lose Heat
heat Exchangewith
THE ENVIRONMENT
Heat Loss by Convection Occurs When the Body Warms Air or Water
Heat Loss by Conduction OccursWhen the Body Is in Contact with a Cooler Surface
Heat Loss by Radiation OccursWhen Infrared Radiation Emitted by the Body Is Absorbed by Cooler Objects
Heat Loss by Evaporation OccursWhen the Water in Sweat, Saliva, and Respiratory Secretions Is Converted into WaterVapor
TEMPERATURE REGULATION
Mammals and Birds Regulate the Input and Output of Heat to Maintain Body TemperatureWithin a Narrow Limit
Temperature-Sensitive Receptors Are Located in the Central Nervous System, the Skin, and Some Internal Organs
Information from Central and Peripheral Meat-Sensitive Neurons Is Integrated in the Hypothalamus to Regulate Heat-Losing or Heat- Conserving Mechanisms
INTEGRATED RESPONSES
The Responses to Heat Stress Are Peripheral Vasodilation and Increased Evaporative Cooling
The Responses to Cold Stress Are Peripheral Vasoconstriction, Piloerection, and Increased Metabolic Heat Production by Shivering and Nonshivering Thermogenesis
Fever Is an Elevation of Body Temperature That Results from an Increase in the Thermoregulatory Set Point
HEAT STROKE, HYPOTHERMIAfAND FROSTBITE
Heat Stroke Occurs When Heat Production or Input Exceeds Heat Output, so Body Temperature Rises to Dangerous Levels
Hypothermia OccursWhen Heat Output Exceeds Heat Production, so Body Temperature Decreases to Dangerous Levels
Frostbite Occurs When Ice Crystals Form in the Tissues of the Extremities
CLINICAL CORRELATIONS
Influenza in Pigs
Heat Stroke in a Boston Terrier
Bibliography
PRACTICE QUESTIONS
The Immune System
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Antigens and Innate Immunity
KEY POINTS
The immune system performs two vital functions that are critical for the maintenance of homeostasis and survival:
ANTIGENS
Antigens (or Immunogens) Stimulate Immune Cells to Induce an Immune Response
The Degree of Immune Response Depends on Several Characteristics of the Antigen
BODY'S DEFENSE AGAINST INVADING ANTIGENS
Both Nonimmune and Immune Mechanisms Defend Against Invading Antigens
A First Line of Defense Includes the Skin and Certain External and Internal Body Fluids
A Second Line of Defense Consists of Phagocytic Cells of the Myeloid and Macrophage-Monocyte Lineages
Macrophage-Derived Cytokines Can Induce a Variety of Physiological Processes to Help Combat Infectious Antigens
CLINICAL CORRELATIONS
Swollen Lymph Nodes in a Colt
Bibliography
PRACTICE QUESTIONS
The Specific Immune Response: Acquired Immunity
KEY POINTS
As discussed in Chapter 54, innate immunity offers effective defense against a wide range of pathogens. Key features of innate immunity include (1) rapid response against invading pathogens, (2) nonspecificity, and (3) physical, chemical, and cellular (phagocytic cells, NK cells) barriers.
T CELLS (T LYMPHOCYTES)
Mature T Cells Develop from Lymphoid Stem Cells That Have Migrated to the Thymus
T Cells Are a Heterogeneous Population of Cytotoxic T Cells and T-Helper Cells
INTERACTIONS OF ANTIGEN- PRESENTING CELLS AND T CELLS
Major Histocompatibility Complex (MHC) Proteins Are Considered the Centrai Regulators of the Immune System
MHC Class I Antigens of Infected Nucleated Cells Play a Major Role in Activating Cytotoxic T Cells
MHC Class Il Antigens on Antigen- Presenting Cells Play a Major Role in Selective Activation of T-Helper Cells
ANTIBODIES
Initial Exposure to Foreign Antigen Induces Slow Onset OfAntibody Appearance, Whereas Subsequent Exposure Induces Faster, Longer- Lasting Antibody Appearance
Antibodies, or Immunoglobulins, Are Glycoprotein Molecules That Can Be Divided into Five Isotypes, or Classes
The B-Cell Population Produces Antibodies to Millions of Different AntigensfYet the Antibody-Antigen Interaction Is Specific
Expansion of an Antigen-Specific B-Memory Cell Population on Initial Antigen Exposure Results in a Faster, More Pervasive, Secondary Immune Response
REGULATION OF IMMUNE RESPONSES
The Actions, Secretions, and Surface Molecule Expression of Immune Cells Play an Important Role in Regulation of the Body's Immune Response

Books and textbooks on the discipline Veterinary anatomy and physiology of animals:

  1. Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p. - 2026 ãîä
  2. Das Pradip Kumar, Sejian V., Mukherjee J., Banerjee D. (eds.). Textbook of Veterinary Physiology. Springer,2023. — 795 p. - 2023 ãîä
  3. Skerritt G.. King's Applied Anatomy of the Abdomen and Pelvis of Domestic Mammals. Wiley-Blackwell,2022. — 180 p. - 2022 ãîä
  4. Rutland Catrin (ed.). Canine Genetics, Health and Medicine. ITexLi,2021. — 165 p. - 2021 ãîä
  5. Singh Baljit. Dyce, Sack and Wensing's Textbook of Veterinary Anatomy. 5th edition. — Elsevier,2018. — 1606 p. - 2018 ãîä
  6. Recce William O., Rowe Eric W.. Functional Anatomy and Physiology of Domestic Animals. 5th edition. — Wiley-Blackwell,2017. — 823 p. - 2017 ãîä
  7. Frandson Rowen D. et al.. Anatomy and Physiology of Farm Animals. 7th Edition. — John Wiley & Sons,2013. — 520 p. - 2013 ãîä
  8. Thomson C.E., Hahn C.. Veterinary Neuroanatomy. Boston: Elsevier,2012. — 378 p. - 2012 ãîä
  9. Dyce K.M., Wensing C.J.G.. Textbook of Veterinary Anatomy. 4th edition. — Saunders,2010. — 846 p. - 2010 ãîä
  10. De Iuliis G., Pulera D.. The Dissection of Vertebrates: A Laboratory Manual. Academic Press,2006. — 304 p. - 2006 ãîä
  11. O'Malley B.. Clinical Anatomy and Physiology of Exotic Species.Germany: Elsevier Saunders,2005. — 257 p. - 2005 ãîä
  12. Sebastiani A.M., Fishbeck D.W.. Mammalian Anatomy: The Cat. 2nd ed. — Morton Publishing Company,2005. — 192 p. - 2005 ãîä
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