SKELETAL SYSTEM 5 Functions of the Skeletal System

SKELETAL SYSTEM

5 Functions of the Skeletal System • Support/structure – upright posture • Movement – attachment for muscles of movement (skeletal muscles) • Protection – surrounds many organs • Mineral storage – mostly calcium, also phosphorous, Na, K • Blood cell formation – produced by red marrow in some bones (hematopoiesis)

BONES= CONNECTIVIE TISSUE -- very active, living , in constant state of fluctuation, not lifeless

Classification of Bones

A. LONG- long, longitudinal axes, expanded ends EX: forearm, thigh bone [femur] B. SHORT- cubelike EX: bones of wrist, ankle [tarsal of ankle] C. FLAT- platelike with broad surfaces EX: ribs, scapula, skull [parietal bone of skull] D. IRREGULAR- variety of shapes, connected to other bones EX: facial bones, [vertabrae] E. SESAMOID- small, nodular embedded in tendons EX: [patella]

Parts of a Bone Epiphysis – expanded ends of the bone • articulates (contacts) other bones • coated w/ a type of articular cartilage (hyaline cartilage) Diaphysis – long central shaft, b/w the epiphyses Periosteum – sheet of dense, connective tissue • covers bones except where artic cart. is present. • Many blood vessels, osteoblasts (bone cells) • Merges w/ tendons and ligaments • bone repair and growth

Medullary Cavity – hollow space in diaphysis • filled w/ yellow marrow (fat for energy storage; body has ability to change yellow marrow red marrow if needed). • interior is lined w/ a membrane called endosteum.

2 Types of Bone Tissue Compact bone – solid, strong, resistant to bending – make up the walls of diaphysys -- small amount covers outside of epiphyses Spongy (cancellous) bone – many, tiny, interconnecting plates of bone – mostly in epiphysys; small amount in the diaphysis. – contains small spaces filled w/ red marrow

MICROSCOPIC STRUCTURE • 3 Types of Bone Cells Osteoblasts – “youthful” bone cells -- build bone tissue -- secrete a large amount of mesenchyme (bone matrix), which hardens to become bone tissue Osteocytes – “older”, mature bone cells -- produce less mesenchyme -- trapped in a chamber (lacunae) Osteoclasts – have the job of crushing, or breaking down bone tissue

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