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  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 - sification/files/ossification1.html sification/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 D 3 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 &q=osteoblasts&total=10&st art=0&num=10&so=0&type=search&plindex= &q=osteoblasts&total=10&st art=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 o.html o.html

Types of Fractures

Aging and Skeletal System Reduction in bone mass occurs between ages 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

Bone Markings