뒤로Bone and Cartilage Structure and Function
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Three types: hyaline (most abundant, glassy, flexible support), elastic (more elastic fibers, found in external ear and epiglottis), and fibrocartilage (thick collagen fibers, resists compression and stretch, found in menisci and intervertebral discs).
Appositional growth: new matrix secreted on cartilage surface by perichondrium cells.
Interstitial growth: chondrocytes divide within lacunae, expanding cartilage from inside.
Support body framework, protect organs, anchor muscles for movement, store minerals (calcium, phosphate), produce blood cells in marrow, store triglycerides in yellow marrow, and produce hormone osteocalcin.
Long bones: longer than wide, with shaft and two ends.
Short bones: cube-shaped (e.g., wrist bones).
Flat bones: thin, flattened (e.g., sternum, skull bones).
Irregular bones: complex shapes (e.g., vertebrae, hip bones).
Axial skeleton: skull, vertebral column, rib cage; supports and protects.
Appendicular skeleton: limbs and girdles; facilitates movement and manipulation.
Consists of diaphysis (shaft) with medullary cavity containing yellow marrow, epiphyses (ends) with spongy bone and articular cartilage, periosteum covering outside, and endosteum lining internal surfaces.
Compact bone: dense, smooth outer layer.
Spongy bone: internal, porous network of trabeculae filled with marrow.
Periosteum: outer fibrous and osteogenic layers covering bone except joints.
Endosteum: delicate membrane lining internal bone surfaces and canals.
Osteoprogenitor cells: stem cells that become osteoblasts.
Osteoblasts: bone-forming cells secreting osteoid.
Osteocytes: mature bone cells maintaining matrix.
Bone lining cells: maintain matrix on inactive surfaces.
Osteoclasts: bone-resorbing cells breaking down matrix.
Osteon is the structural unit of compact bone, composed of concentric lamellae with collagen fibers alternating direction to resist torsion, surrounding a central canal with blood vessels and nerves.
Tiny canals connecting osteocytes in lacunae, allowing nutrient and waste exchange and cell communication through gap junctions.
Organic: cells and osteoid (collagen and ground substance) provide tensile strength and flexibility.
Inorganic: hydroxyapatite mineral salts provide hardness and resistance to compression.
Bone forms by replacing hyaline cartilage; involves bone collar formation, cartilage calcification, periosteal bud invasion, diaphysis elongation, and secondary ossification centers in epiphyses.
Bone develops directly from mesenchymal fibrous connective tissue membranes, forming flat bones like skull and clavicles through ossification centers and osteoid secretion.
1. Resting zone (inactive cartilage)
2. Proliferation zone (rapid cell division)
3. Hypertrophic zone (enlarging chondrocytes)
4. Calcification zone (matrix calcifies, chondrocytes die)
5. Ossification zone (new bone forms)
Continuous cycle of bone resorption by osteoclasts and bone deposition by osteoblasts, regulated by hormones and mechanical stress to maintain bone strength and calcium homeostasis.
Parathyroid hormone (PTH) increases blood Ca2+ by stimulating osteoclasts.
Calcitonin lowers blood Ca2+ but has minor effect in adults.
Vitamin D enhances calcium absorption.
Bones remodel and grow stronger in response to mechanical stress, with thickening where stress is greatest and trabeculae aligned along lines of compression.
1. Hematoma formation
2. Fibrocartilaginous (soft) callus formation
3. Bony (hard) callus formation
4. Bone remodeling to restore original shape
Comminuted (multiple fragments), compression (bone crushed), spiral (twisting), epiphyseal (at growth plate), depressed (inward skull fracture), greenstick (incomplete break in children).
Bone resorption exceeds deposition, causing porous, fragile bones prone to fractures, especially in postmenopausal females due to decreased estrogen.
Disorders of poor bone mineralization due to vitamin D or calcium deficiency; rickets affects children causing bone deformities, osteomalacia affects adults causing soft bones.
Excessive and disorganized bone remodeling leading to weak, deformed bones with high spongy to compact bone ratio; often affects spine, pelvis, femur, and skull.
Bone mass decreases with age due to increased resorption; more incomplete osteons, less mineralization, slower fracture healing; females more affected due to hormone changes.