Chapter 55 - Skeletal Development

Question 1

Intramembranous ossification

Answer 1

formation of calcified osteoid matrix INSIDE of a cartilage framework

flat bones, clavicles, and the skull

Question 2

Endochondral ossification

Answer 2

occurs at growth plates and within fracture callous and is characterized by osteoid production ONTO a cartilage anlage

Question 3

cellular zones of the physis

Answer 3

1. reserve zone - sparse distribution of cells in a vast matrix, chondrocytes are not participating in longitudinal growth, type II collgen is highest here
2. proliferative zone - longitudinal columns of flattened cells, uppermost cell is the progenitor cell and is responsible for longitudinal growth
   - maturation zone
3. hypertrophic zone - weakest layer, novel matrix protein synthesis occurs here, chondrocytes participate in matrix mineralization thru alkaline phosphatase synthesis, neutral protease synthesis, type X collagen synthesis

Question 4

what effect does PTH have on physeal chondrocytes

Answer 4

preferentially effects proliferative and upper hypertrophic zone chondrocytes
- has a direct mitogenic effect on these chondrocytes
- increases proteoglycan synthesis

Question 5

the level of vitamin D metabolites is highest in which physeal regoin>

Answer 5

the proliferative zone
- no metabolites are found in the hypertrophic zone

Question 6

what is the weakest region within the physis?

Answer 6

zone of hypertrophy

Question 7

hypophosphatasia

Answer 7

Autosomal recessive defect in alkaline phosphatase
normal levels of calcium nd phosphate
inability to calcify matrix
WIDENED hypertrophic zone
zone of provisional calcification never forms

Question 8

hypophosphatemic rickets

Answer 8

X-linked dominant
low serum calcium
low serum phosphorous
alkaline phosphatase activity is high
abnormal conversion of vitamin d to its metabolites

Question 9

bacterial infection affects which portoin of the epiphyseal plate?

Answer 9

metaphyseal region

Question 10

radiation affects which region of the epiphyseal plate preferentially?

Answer 10

zone of proliferation

Question 11

XR findings unique to rickets

Answer 11

widened zone of hypertrophy
metaphyseal flaring

Question 12

scurvy

Answer 12

vitamin C deficiency
decreased chondroitin sulfate and collagen synthesis
seen preferentially at the metaphysis where tI collagen is highest

Question 13

XR findings of scurvy

Answer 13

frenkel lines - radiodense lines representing the zone of provisional calcification
metaphyseal flaring
metaphyseal osteopenia