Chapter 12 — Chapter 12 — Human Skeletal and Muscular Systems

Bone: hard connective tissue — matrix of collagen fibres (flexibility) and calcium phosphate (hydroxyapatite, hardness). Cells: osteoblasts (build bone, secrete matrix), osteocytes (mature bone cells in lacunae, maintain matrix, connected by canaliculi), osteoclasts (large multinucleate, resorb bone, release Ca²⁺). Compact bone: dense, outer layer, Haversian systems (osteons) — central Haversian canal with vessels and nerves surrounded by concentric lamellae; Volkmann's canals. Spongy (cancellous) bone: trabeculae network with red marrow, at ends of long bones; lighter. Long bone: diaphysis (shaft with marrow cavity, yellow marrow), epiphyses, periosteum, endosteum, articular cartilage. Cartilage: chondrocytes in lacunae in a firm flexible matrix (chondroitin), avascular, perichondrium. Hyaline (glassy, fine collagen; articular surfaces, nose, trachea, costal), elastic (elastic fibres; ear pinna, epiglottis), fibrocartilage (dense collagen bundles; intervertebral discs, pubic symphysis, menisci).