anatomy Bone Tissue

Four classes of bones by shape

Long, short, flat, and irregular bones.

Examples of long bones

Femur, humerus, radius, ulna, tibia, and fibula.

Shape of short bones

Cube-like, with roughly equal lengths and widths.

Examples of short bones

Carpals (wrist bones) and tarsals (ankle bones).

Shape of flat bones

Plate-like structures with broad surfaces.

Examples of flat bones

Ribs, scapulae, and most bones of the skull.

Irregular bones

Bones with varied, complex shapes, such as vertebrae and facial bones.

Sesamoid bones

Small, nodular bones embedded within tendons (e.g., the patella).

Epiphysis

The expanded end of a long bone that articulates with another bone.

Articular cartilage

Hyaline cartilage layer coating the articulating portion of an epiphysis.

Diaphysis

The shaft of a long bone.

Periosteum

A tough, fibrous vascular covering enclosing a bone, except for articular cartilage.

Functions of periosteum

Helps form and repair bone tissue; provides attachment sites for tendons/ligaments.

Compact bone vs. Spongy bone location

Compact bone forms the diaphysis wall; spongy bone largely fills the epiphyses.

Trabeculae (bony plates)

Branching bony plates that make up spongy bone.

Medullary cavity

A hollow chamber/canal running through the diaphysis of a long bone.

Endosteum

A thin membrane of connective tissue lining the medullary cavity.

Marrow

Specialized soft connective tissue filling bone spaces (red or yellow marrow).

Osteocytes

Mature bone cells located in tiny, bony chambers called lacunae.

Canaliculi

Tiny canals through which cellular processes of osteocytes pass to share nutrients.

Composition of bone intercellular matrix

Inorganic salts (calcium phosphate) and organic collagen fibers.

Osteon (Haversian system)

The cylinder-shaped structural unit of compact bone.

Perforating canals (Volkmann's canals)

Canals connecting central canals, containing larger blood vessels and nerves.

Intramembranous bones

Bones originating within sheet-like layers of connective tissue (e.g., flat skull bones).

Endochondral bones

Bones originating as hyaline cartilage models that are later replaced by bone.

Osteoblasts

Bone-forming cells that deposit bony matrix.

Osteoclasts

Multinucleated cells that break down calcified bone matrix.

Epiphyseal plate

A band of hyaline cartilage between the diaphysis and epiphysis where growth occurs.

Bone homeostasis (remodeling)

Continuous action of osteoclasts resorbing bone and osteoblasts depositing bone.

Vitamin D function in bone

Necessary for proper absorption of calcium in the small intestine.

Vitamin C requirement in bone

Required for collagen synthesis.

Growth hormone effect on bone

Stimulates division of cartilage cells in epiphyseal plates.

Hematopoiesis

The process of blood cell formation.

Red marrow vs. Yellow marrow

Red marrow forms blood cells; yellow marrow stores fat.

Average number of bones in adult human skeleton

206 bones.

Two major divisions of the skeleton

Axial skeleton and appendicular skeleton.

Axial skeleton components

Skull, hyoid bone, vertebral column, and thoracic cage.

Appendicular skeleton components

Pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

Pectoral girdle components

Scapulae (shoulder blades) and clavicles (collarbones).

Pelvic girdle components

Two hip bones (coxal bones) connecting the lower limbs to the sacrum.