Bone Anatomy and Tissue Quiz

Bone Anatomy

• Bones are mineralized connective living tissue, not static. They have growth and death cycles.
• Bones have blood vessels (arteries and veins) and nerves for supply.
• They are made up of compact and spongy tissues.
• Bones form the basis of the skeleton, consisting of osseous cells and having a dense, hard structure.
• The outer layer is compact tissue, and the inner layer is cancellous (spongy) tissue.
• A hollow space within long bones is called the medullary cavity.

Bone Structures

• Periosteum: A thick, outer membrane layer, absent over articular ends. It differentiates into two types of membranes:
  • External fibrous layer: Attaches to muscles, tendons, ligaments and blood vessels.
  • Internal osteogenic layer: Acts as a bone-forming layer, helping in retaining partially fractured fragments.
• Endosteum: Lines the medullary cavity of long bones, also known as the medullary membrane. It is highly vascularized and contains a nerve supply.
• Marrow: A soft, fatty substance filling the medullary cavity and cancellous tissue spaces in long bones. Two types:
  • Red marrow: Reddish in color, found in young animals, consisting of fat cells.
  • Yellow marrow: Yellowish in color, found in adult animals, consisting of fat cells.

Parts of a Long Bone

• Diaphysis: The middle part of the long bone, forming its shaft, and ossifies from the primary ossification center.
• Epiphysis: Generally forms the ends of long bones, with three types:
  • Pressure epiphysis: Carries the body weight (e.g., head and condyles of the femur.)
  • Traction epiphysis: Formed by the pull of muscles (e.g., trochanter of the femur.)
  • Atavistic epiphysis: When one bone attaches to another for nutrition (e.g., coracoid process of the scapula).
• Metaphysis: Located between diaphysis and epiphysis.
• Epiphyseal cartilage: A plate of hyaline cartilage found between the diaphysis and epiphysis in growing long bones. In adults, it is replaced by bone.

Compact Bone Tissue

• Haversian system (Osteons): A definite pattern of bony tissue arrangement.
• Haversian canal: A narrow, hollow space that runs through compact bone and carries blood vessels and nerves.
• Haversian lamellae: Concentric layers of osseous deposition surrounding the Haversian canal, ranging from 2-6 layers.
• Lacunae: Tiny spaces between lamellae that house osteocytes.
• Canaliculi: Radiating canals extending from lacunae, connecting osteocytes to the Haversian canal.
• Haversian cylinder: A structural unit of compact bone.

Cancellous Bone Tissue

• Cancellous tissue is made up of thin bony plates in divergent directions.
• Haversian systems are absent in cancellous bone.
• It is found in smaller amounts in the shaft and more at the extremities of long bones.
• It comprises the main mass in short and irregular bones.

Bone Cells

• Osteoblasts: Bone-forming cells derived from mesenchymal cells, producing calcium ions and alkaline phosphatase for matrix precipitation. Their nucleus is eccentric, and they have numerous cytoplasmic processes.
• Osteoclasts: Multinucleated cells that resorb bone. Their cytoplasmic processes are absent and they have a brush border.
• Osteocytes: Derived from osteoblasts, residing in lacunae within the bone matrix, with numerous cytoplasmic processes and a centrally located nucleus.

Bone Composition

• Organic matter: Makes up 30-40% of bone, contributing to its growth and development. It includes membranes, cartilage, marrow, vessels, and nerves.
• Inorganic matter: Comprises 60-70% of bone, providing strength and hardness. The major inorganic component is calcium phosphate (86%), with smaller amounts of calcium carbonate, magnesium phosphate, and sodium carbonate/fluoride.

Ossification

• Ossification is the process of bone formation.
• Intra-membranous ossification: A type of bone formation originating from mesenchymal cells, predominantly in flat bones of the skull. Osteoblasts produce collagen matrix, which then calcifies.
• Endochondral ossification: A type of bone formation that begins in cartilage models, primarily forming most long bones. Cartilage cells differentiate, and eventually are replaced by bone. This process occurs in three stages:
  • Stage I: Formation of the hyaline cartilage model and the development of periosteum.
  • Stage II: Formation of the sub-periosteal collar bone and the invasion of the periosteal bud.
  • Stage III: Formation of the lamellated bone, replacement of bone matrix by osteocytes, and the expansion of the marrow cavity.

Types of Bones

• Long bones: Found in limbs, characterized by a shaft and two expanded ends containing a medullary cavity filled with marrow (e.g., femur, humerus).

• Short bones: Small, piece-like bones, found in joints, assisting mobility (e.g., carpals).

• Flat bones: Flat, irregular, plate-like bones enclosing body cavities and having wide and extensive muscle attachments; composed of two compact bone layers with spongy tissue between (e.g., scapula, bones of the skull).

• Irregular bones: Unpaired, irregular shaped bones helping in various muscle attachments; composed of spongy bone covered by compact bone (e.g., vertebrae).

• Pneumatic bones: Some long bones having air cavities inside their bodies (e.g., humerus of birds, certain skull bones).

• Sesamoid bones: Small, seed-like bones developing within tendons; assisting in reducing friction.

• Visceral Bones: Found within the viscera of animals and birds (e.g., os-optic -eyes of birds, os-cordis-heart of ox, os-penis-penis of dog).