Bone Physiology

Question 1

What is the epiphysis

Answer 1

Head
Articular surface

Question 2

What is the diaphysis

Answer 2

Shaft

Question 3

What is the metaphysis

Answer 3

Growth plate

Question 4

What are 3 examples of flat bones

Answer 4

Skull, ribs and sternum

Question 5

What are the 4 bone types

Answer 5

Sesamoid
Short
Irregular
Alveolar bone of the jaw

Question 6

What is intramembranous formation

Answer 6

Bone forms directly from mesenchymal cells

Question 7

What is endochondral ossification

Answer 7

Bone forms from a cartilaginous template
Morphogenesis and growth phases

Question 8

What happens during intramembranous formation

Answer 8

Mesenchymal condensations form early in embryogenesis
Differentiate into osteoblasts form osteoid which mineralises

Question 9

How is intramembranous formation genetically regulated

Answer 9

By patterning genes encoding transcription factors such as homeobox (HOX) or paired box (PAX)

Question 10

What is the first stage of endochondral ossification

Answer 10

Mesenchymal cells form condensations (lateral plate mesoderm)

Question 11

What is the second stage of endochondral ossification

Answer 11

Differentiate into chondrocytes and begin to proliferate and secrete cartilaginous matrix

Question 12

What is the third stage of endochondral ossification

Answer 12

Chondrocytes differentiate into hypertrophic chondrocytes

Question 13

What is the last stage of endochondral ossification

Answer 13

Blood vessels invade cartilaginous matrix. Surrounding perichondrial cells differentiate into osteoblasts forming the primary ossification centre

Question 14

What is the secondary ossification of endochondral ossification

Answer 14

Appear in the epiphyses forming the articular surfaces of the bone

Question 15

What are the 5 zones of the growth plate

Answer 15

Resting zone
Proliferative zone
Pre hypertrophic zone
Hypertrophic zone
Invasion zone

Question 16

How are chondrocytes arranged in the growth plate

Answer 16

In columns

Question 17

How is proliferation and differentiation in growth plate

Answer 17

Are tightly regulated

Question 18

Which type of bone is the main site of calcium exchange

Answer 18

Trabecular, spongy, cancellous

Question 19

What are 3 types of cells in bone marrow

Answer 19

Erythrocytes
Lymphocytes
Cells of the myeloid lineage

Question 20

What do bone lining cells detect

Answer 20

Changes in loading environment and expose bone surface for resorption

Question 21

What is the main mechano sensitive bone cell

Answer 21

Osteocytes

Question 22

What is osteoblastic lineage

Answer 22

Stromal precursors that are capable of forming either osteoblasts or adipose cells

Question 23

What is osteoclastic lineage

Answer 23

Myeloid

Question 24

What are 4 physiological factors that impact on bone homeostasis

Answer 24

Fluctuations in serum calcium
Changes in mechanical loading
Repair of micro fractures
Hormonal status

Question 25

What are the 5 stages of bone formation and resorption

Answer 25

Resting bone surface Resorption Reversal Bone formation Mineralisation

Question 26

What do osteoblasts synthesise

Answer 26

The organic matrix of bone (osteoid) and control its mineralisation

Question 27

After finishing making new bone what 3 cells can osteoblasts differentiate into

Answer 27

Osteocytes Bone lining cells Undergo apoptosis

Question 28

What do osteoclasts form from

Answer 28

Pluripotent CD34+ mononuclear phagocytes precursors that can form many myeloid cell types

Question 29

What 2 physiological regulators are osteoclast differentiation and bone resorption

Answer 29

Low serum Ca2+ levels (calcium homeostasis) Decreases in mechanical loading

Question 30

What 3 pathological regulators of osteoclasts

Answer 30

Disruption of steroid hormone levels Inflammation Cancer

Question 31

What does RANKL bind to

Answer 31

It’s receptor RANK on osteoclast precursors

Question 32

What does osteoblastic osteoprotegerin (OPG) do

Answer 32

Further layer of control which is a soluble decoy receptor for RANKL

Question 33

What is the first process of bone resorption

Answer 33

Attaches to surface through a5 b3 integrin interaction with RGD containing proteins

Question 34

What is the second process of bone resorption

Answer 34

Polarisation of osteoclast formation of ruffled border, actin ring and sealed zone

Question 35

What is the third process of bone resorption

Answer 35

Acidification of the sealed zone by active transport of H+ to breakdown mineral component of bone. Oc pH maintained by Cl-/HCO3- exchanger on basolateral surface

Question 36

What is the fourth process of bone resorption

Answer 36

Release of cathepsin K and other proteases that digest collagen

Question 37

What is the fifth process of bone resorption

Answer 37

Creates a resorption pit 4-5uM deep