1. Skeletal System Lecture #2
LTs 2, 4 & 5
Skeletal Overview

2. The skeleton protects, supports and permits movement
Classification of 206 bones:
Long bones – limbs, finger, palm, arch of foot
Short bones – wrists, ankles
Flat bones – cranium, sternum, ribs, (patella)
Irregular bones – sacrum, vertebrae, hyoid

3. Development of bone
Chondroblasts – cartilage forming cells of earliest stages of fetal development
At 2-3 months in utero the cartilage models begin to dissolve and are replaced by bone = ossification
When chondroblasts die the matrix they produced breaks down making room for blood vessels

6. Bone Development cont’d
Blood vessels carry osteoblasts (Gk bone + to form) from the periosteum into the area where the matrix was.
Osteoblasts secrete osteoid (a mixture of proteins and collagen) that becomes bone
Osteoblasts also secrete enzymes that help
form hydroxyapatite (crystals of hard mineral salts around the osteoid matrix)

7. Bone Development cont’d
Mature osteocytes become embedded in hardened lacunae & maintain bone matrix
Bones lengthen throughout childhood & adolescence because of the growth plate in each epiphysis
As bone lengthens the plates at each end grow farther apart
Bones also grow in width as osteoblasts lay down bone just below periosteum

8. Bone development controlled by hormones
Growth hormone during preadolesence
Sex hormones during puberty stimulate growth plates at first
By 18 in women and 21 in men those same sex hormones signal the growth plates to stop growing
Growth plates close but bones can still grow wider

9. 8 Types of Fractures Simple – skin intact Compound – skin pierced
Complete – bone in 2 parts
Partial – longitudinal break
Greenstick – outer arc of bone only
Impacted – bone ends wedged into each other
Comminuted – “shattered”
Spiral – ragged break due to twisting

10. Repair - fractures
First a blood clot or hematoma forms at the break site as the bone bleeds
Inflammation, swelling & pain immobilize the area
Repair begins within days as fibroblasts migrate to the area & form a fibrocartilage callus-
collagenous fibers bind ends together
A bony callus is formed as osteoblasts lay down trabeculae replacing the fibrocartilage callus-joins bones
Remodeling – compact bone is laid down on outsides by osteoblasts and osteoclasts reabsorb the spongy bone  medullary cavity

12. Repair
Bones rarely break in the same place twice because the repaired area is thicker than the original bone
The repair process slows with age and applications of weak electrical current can increase the rate of healing – perhaps by attracting osteoblasts