Unit 2

Question 1

Intramembranous Ossification location

Answer 1

Bone me of the skull and part of clavicle

Question 2

Intramembranous ossification process

Answer 2

1. Mesenchyne clustering
   Formation of osteoid
   Differentiation into osteoblasts/osteocytes
2. Compact bone formation
   Initiated by trapped vessels

Question 3

Endochondral ossification steps:

Answer 3

1. Cartilage model in early embryonic life.
   Model grows
   Calcification
2. Perichondrium
   Blood vessels encircle cartilage model
   Osteoblast differentiation
   Bone layer produced: periosteum
3. Primary center of ossification established
   Blood vessel penetrates
   More ossification
4. Medullary cavity established
   Spongy bone eroded by osteoclasts
5. Secondary centers of ossification
   After birth at epiphyses
6. Maturity
   Spongy bone in epiphyses
   Articulate cartilage remains
   Growth continues until plate ossifies

Question 4

Intramembranous ossification process:

Answer 4

1. Mesenchyme clustering
   Formation of osteoid and differentiation into osteoblasts/osteocytes
2. Compact bone formation
   Initiated by trapped vessels

Question 5

Appositional growth

Answer 5

Increasing diameter, outer layer deposited and inner layer reabsorbed

Question 6

Blood Ca too high (calcitrol)

Answer 6

Calcitrol: increases blood calcium absorption in intestines
-increases osteolysis
Inhibits calcium excretion

Question 7

Low ca blood level

Answer 7

Parathyroid hormone
Stimulus: blood calcium low (8.5 mg/dl)
Receptor: ca sensing (chief) cells of the PTG
Control center: chief cells of PTG
Message:PTH
Effectors: osteoclasts, kidney tubule cells, intestinal cells
Response: stimulated osteoclasts, kidneys reabsorb more ca, kidneys synthesize calcitrol, intestines more permeable to ca, inhibit collagen synthesis in osteoblasts, bone deposition inhibited

Question 8

Blood levels high

Answer 8

Stimulus: Blood ca levels high (11 mg/dl)
Receptors: C cells of the thyroid gland
Control center: C cells of the thyroid gland
Message: Calcitonin
Effectors: Osteoclasts, kidney tubule cells, intestinal cells
Response: osteoclasts inhibited, ca reabsorption at kidney tubules (excretion), ca reabsorption inhibited at intestines

Question 9

Osteoblasts

Answer 9

Bone building cells
Turn osteoid into bone
Mature into osteocytes

Question 10

Osteogenic cells

Answer 10

Derived from mesenchyme

For growth and repair

Question 11

Osteocytes

Answer 11

Mature bone cells
Live in lacunae
Communicate via canaliculi
Can build or break bone

Question 12

Osteoclasts

Answer 12

Break down bone matrix
Allow for osteolysis…
Release ca
Multinucleate

Question 13

Hydroxyapatite

Answer 13

Calcium and phosphate salt