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- http://commons.bcit.ca/biology/os

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 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=-6243626

796969590657&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

Types of Fractures

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

Bone Markings

Bone Markings