INTRODUCTION TO BONE PHYSIOLOGY

14.1.1 Definition of Bones

Bones are rigid organs that form the skeletal system of vertebrates, including mammals, birds, reptiles, amphib­ians, and fish. They serve as the structural framework of the body, providing support, protection, and anchorage for muscles.

14.1.2 Importance of Bones in Animals

a. Structural Support:

Bones provide structural support for the body, giving it shape and stability. They form the framework that holds the body upright and allows animals to move.

b. Protection of Vital Organs:

Bones serve as protective coverings for vital organs such as the brain, spinal cord, heart, and lungs. The skull protects the brain, while the ribcage shields the heart and lungs from injury.

c. Muscle Attachment:

Bones serve as attachment sites for muscles, tendons, and ligaments. Muscles attach to bones via tendons, allowing movement of body parts when muscles contract.

d. Facilitation of Movement:

Bones, along with muscles and joints, enable animals to move. They form levers that muscles pull on to produce movement. Different shapes and arrangements of bones facilitate various types of movement, from running and jumping to flying and swimming.

e. Blood Cell Production:

Within the cavities of certain bones, such as the marrow cavity of long bones, hematopoiesis occurs. Hematopoiesis is the process of blood cell formation, including red blood cells, white blood cells, and platelets. These blood cells play vital roles in oxygen transport, immune response, and blood clotting.

f. Mineral Storage and Homeostasis:

Bones store essential minerals such as calcium and phos­phorus, which are important for bone strength and integ­rity.

14.1.3 Overview of Bone Structure

1. M acroscopic Structure:

a. Compact Bone: Also known as cortical bone, compact bone forms the dense outer layer of bones. It consists of multiple layers called lamellae, which are arranged in concentric circles around central canals called Haversian canals. These canals contain blood vessels, lymphatic vessels, and nerves that supply nutrients to the bone tissue.

b. Spongy Bone: Also called cancellous or tra­becular bone, spongy bone forms the inner layer of bones. It consists of a network of bony trabeculae or spicules separated by spaces filled with bone marrow. Spongy bone pro­vides structural support while reducing the overall weight of the bone.

2. Microscopic Structure:

a. Osteocytes: Osteocytes are mature bone cells embedded within the bone matrix. They main­tain bone tissue by regulating mineral content and responding to mechanical stress.

b. Osteoblasts: Osteoblasts are bone-forming cells responsible for synthesizing and secret­ing organic components of the bone matrix, such as collagen. They play a crucial role in bone growth and repair.

c. Osteoclasts: Osteoclasts are multinucle­ated cells responsible for bone resorption, the process of breaking down bone tissue. They secrete enzymes and acids that dissolve

FIGURE 14.1 Physiology of bones in brief

mineralized bone matrix, releasing calcium and phosphorus into the bloodstream.

d. Bone Matrix: The bone matrix consists of organic and inorganic components. The organic matrix is predominantly composed of collagen fibers, which provide tensile strength and flexibility to the bone. The inorganic matrix consists primarily of hydroxyapatite crystals, composed of calcium phosphate, which provides compressive strength and rigidity to the bone.

e. Bone Marrow: Bone marrow is a soft, gelati­nous tissue found within the medullary cavi­ties of long bones and in the spaces between trabeculae of spongy bone. It consists of two types: red bone marrow, responsible for hema­topoiesis (blood cell formation), and yellow bone marrow, primarily composed of adipo­cytes (fat cells).

14.1.4 Terminologies and Key Words

The following are a few basic terminologies which a veteri­nary orthopedic surgeon should be aware of.

1. Bone Composition: Bones are composed of organic components (e.g., collagen) and inorganic components (e.g., hydroxyapatite) that provide strength, flexibility, and rigidity to bone tissue.

2. Bone Development: Bones develop through pro­cesses such as intramembranous ossification and endochondral ossification, with growth occurring at epiphyseal growth plates during childhood and adolescence.

3. Bone Remodeling: Boneremodelinginvolvesthecon- tinuous balance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation, which is regulated by various factors including hor­mones, mechanical stress, and nutritional status.

4. Mechanical Properties: Bones exhibit mechani­cal properties such as strength, elasticity, and toughness, which are influenced by factors such as bone density, structure, and mineralization.

5. Factors Affecting Bone Health: Nutrition, exer­cise, hormonal balance, genetics, age, and devel­opmental stage are important factors affecting bone health in animals.

6. Bone Diseases and Disorders: Common bone diseases and disorders in animals include osteo­porosis, osteoarthritis, rickets, osteomalacia, and bone fractures, which can impact mobility, quality of life, and overall health.

7. Comparative Bone Physiology: Bone physiology varies among different animal species based on factors such as size, habitat, locomotor behavior, and evolutionary adaptations.

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