Chapter 2
Geriatrics: Section I - Bone Growth
| TIS | Chapter 2 | |
1) Intramembranous bone
* pre-existing tissue is mesenchyme
* mesenchymal cells turn into osteoblasts
2) Endochondral bone
* pre-existing tissue is hyaline cartilage
II. ENDOCHONDRAL BONE GROWTH
1) Begin with hyaline cartilage model
* perichondrium surrounds cartilage
2) Cartilage model will enlarge
* chondrocytes enlarge, resorb part of cartilage
* rest of cartilage undergoes calcification
* chondrocytes die, leaving hardened matrix
3) At the SAME TIME, perichondrium is invaded by smal blood vessels
* cells turn into osteoblasts
* periochondrium transformed into periosteum
4) Osteoblasts secrete osteoid onto the calcified cartilage
* periosteal bone collar
5) Blood vessels and osteoblasts penetrate inside and occupy spaces in shaft
* bone matrix replaces cartilage
6) Process #5 is repeated at the ends (epiphyses) of the bone
7) Cartilage removed, except at articular surfaces of bone and ends of diaphysis
* cartilage plate between epiphyses and diaphysis:
epiphyseal plate
* lengthwise bone growth
* plate active for 15-25 years
8) As bone develops, new bone is being laid on outside by osteoblasts
* osteoclasts remove bone from inside of diaphysis, creating the medullary cavity
Process of bone formation and removal: bone remodelling
III. DISORDERS OF BONE
A. Rickets:
* found in young children
* caused by Vitamin D deficiency, resulting in poor absorption of calcium
* bone matrix is laid down, but not enough calcium to harden matrix
B. Osteomalacia:
* adults - Vitamin D deficiency
* bone becomes demineralized, warps under gravity
* common in women w/poor diets, repeat pregnancies, little exposure to sunlight
C. Osteoporosis: reduction in bone mass, making skeleton fragile
* common disorder, esp. among elderly
* causes: inadequate calcium uptake, reduced physical activity, & hormonal deficiency
IV. BONE FRACTURES
A. Kinds of fractures:
1. Simple (bone doesn't break through skin) vs. Compound (bone breaks through skin)
2. Partial (bone incompletely broken) vs. Complete (fracture separates bone into two parts)
3. Direction of fracture:
a) spiral: fracture line twisted as it is broken
b) transverse: (complete) fracture occurs at right angles to shaft
c) oblique: fracture occurs at slant to bone shaft
B. Fracture Repair:
1. When bone is broken, blood vessels are torn: a blood clot (fracture hematoma) forms
2. Circulation to nearby osteons is disrupted
* localized death (necrosis) of bone
3. A callus is formed at site of fracture (fibrous CT & cartilage)
* repaired blood vessels enter callus
4. Periosteum lays down a sleeve of bone around callus
* cartilage callus broken down and replaced by bone
