TIS

Chapter 2
Geriatrics: Section I - Bone Growth


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


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