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The Skeletal System. Functions. Support Structural support Framework for attachment Storage Calcium reserve Energy reserves (Lipids in yellow marrow) Blood Cell Production Rbc and wbc produced in red marrow Protection Surrounds soft tissues and organs Leverage
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Functions • Support • Structural support • Framework for attachment • Storage • Calcium reserve • Energy reserves (Lipids in yellow marrow) • Blood Cell Production • Rbc and wbc produced in red marrow • Protection • Surrounds soft tissues and organs • Leverage • Change magnitude and direction of forces generated by skeletal muscles
Macroscopic Features of Bone Structure • Long Bones • Longer than they are wide • Ex. Humerus, femur • Short Bones • Roughly equal length and width • Ex. Carpals, tarsals • Flat Bones • Thin and broad • Ex. Ribs, scapulae, parietal bones of skull • Irregular Bones • Complex shapes
Features of Long Bones • Diaphysis • Central shaft • Bone marrow • Loose connective tissue • Epiphysis • Epanded ends covered w/ articular cartilage • Compact bone • Dense/solid • Found in diaphysis • Spongy (cancellous) bone • Network of bony rods w/ spaces • Found in epiphysis • Periosteum • Covers outer surface of bone • Endosteum • Lines marrow cavity
Microscopic Features of Bone • Histology (central canal, osteocytes, lacunae, canaliculi) • Compact Bone • Haversian system (aka osteons) – arranged in circles • Spongy Bone • Trabecule (rods create network) • Cytology • Osteocytes – mature bone cells • Osteoclasts – giant multinucleated cells that secrete acids and enzymes to dissolve bony matrix and release Ca (osteolysis) • Osteoblasts – produce new bone (osteogenesis) and promotes Ca deposits in bone matrix
Compact Bone vs. Spongy Bone(Ground bone) (Cancellous bone) Note the absence of osteons in spongy bone
Bone Formation and Growth • Ossification – replacing other tissues with bone • Intramembranous – (flat) bone develops within membranes of connective tissue • Endochondrial – (long) bone replaces cartilage • http://commons.bcit.ca/biology/ossification/files/ossification1.html • Calcification – deposition of calcium salts • Body Proportions • Begins at 6 weeks (cartilage skeleton in utero) continues to age 18/25 • Requirements • Prenatal – minerals absorbed from mother (often loses bone mass) • Consume Ca and P from diet • Vitamin D3 allows absorption of Ca and P • Vitamin A and C needed for osteoblast activity
Bone Remodeling • Remodeling • Removal and replacement of protein and minerals from bone • Heavily stressed bones become thicker and stronger • Inactivity (even brief) causes atrophy (degeneration)
Homeostasis and Mineral Storage • 99% Ca deposited in skeleton • Ca+ ions play an important role in both neurological and muscular processes • Ca ion conc. are closely regulated • Parathyroid hormone (PTH) and calcitrol work together to elevate Ca levels in body fluids (bones become weaker) • Calcitonin depresses Ca levels in body fluids (bones become stronger)
Injury and Repair • http://video.google.com/videoplay?docid=-6243626796969590657&q=osteoblasts&total=10&start=0&num=10&so=0&type=search&plindex=1 • Fracture – any crack or break in a bone • Healing can take from 4 months to over a year! • Fracture hemotoma – large blood clot closes injured bv • External and internal calluses – thickenings resulting from mitotic divisions • http://commons.bcit.ca/biology/ossification/files/patho.html
Aging and Skeletal System • Reduction in bone mass occurs between ages 30 -40 • Women lose ~8% skeletal mass per decade • Men lose ~3% per decade • Epiphyses, vertebrae, and jaws most vulnerable • Osteoperosis – decrease in estrogen increases osteoclast activity (so does smoking); other causes include lack of Ca+ in diet, inactive lifestyle, and certain medications
