MSK

Question 1

Bone function

Answer 1

o	Raises body against gravity
o	Determines body shape
o	Transmits body weight
o	Protects vital organs
o	Forms jointed lever system -> movement
o	Storage of bone marrow and minerals

Question 2

Types of bone:

Answer 2

o	Long bones:
	Tubular hollow shaft
	Expanded ends for articulation
	Femur and humerus – most bones
o	Short bones:
	Cuboidal shape
	Carpal bones (wrist)
o	Flat bones:
	Curved plates of bone
	Associated with protection
	Bones of the skull
o	Irregular bones:
	Various shapes
	Vertebrae -> spinal cord protection
o	Sesamoid bones:
	Round, oval bones embedded in tendon
	Patella – knee joint

Question 3

Axial vs appendicular:

Answer 3

o Axial – skull, vertebrae, ribcage, coccyx

o Appendicular – bones of the arms and legs, scapula, pelvis

Question 4

• Macro bone structure:

Answer 4

o	Cortical – dense and compact, only space for cells/blood vessels
o	Trabecular (spongy) – network of bony struts filled with bone marrow

Question 5

• Micro bone structure:

Answer 5

o Woven – quickly made, disorganised bone

o Lamellar – slowly made, organised layers of bone

Question 6

• Intermembranous ossification:

Answer 6

o Produces flat bones – skull, teeth, clavicle

1. Mesenchyme cells -> osteoprogenitor cells -> osteoblasts form primary ossification centre
2. Osteoblasts secrete collagen and proteins -> forms osteoid (bony matrix)
3. Osteoid is calcified -> engulfs osteoblasts to form osteocytes
4. Osteoid is randomly laid down around blood vessels -> trabeculated (osteoblasts are on periphery)
5. Peripheral osteoid becomes compact bone -> spongy bone contains bone marrow

Question 7

• Endochondral ossification:

Answer 7

o Produces most bones in body – long bone most common example
o Embryonically begins as a hyaline cartilage model

1. Collar formation:
2. Cavity formation:
3. Vascular invasion:
4. Elongations:
5. Epiphyseal ossification:

Question 8

1. Collar formation:

Answer 8

 Osteoprogenitor cells -> osteoblasts
 Osteoblasts secrete osteoid
 Bony collar formed around shaft (diaphysis

Question 9

2. Cavity formation:

Answer 9

 Cartilage in bone centre begins to ossify – primary ossification centre
 Inner cartilage can’t get nutrients -> degrades and forms cavity

Question 10

3. Vascular invasion:

Answer 10

 Vessels in periosteum invade cavity through nutrient foramen
 Vessels bring blood, nutrients and osteoblasts/osteoclasts
 Osteoclasts break down cartilage, osteoblasts secrete spongy bone

Question 11

4. Elongations:

Answer 11

 Increased cell numbers + osteoid -> elongation of diaphysis
 Vessels bud into cartilage at ends of bone – secondary ossification centre

Question 12

5. Epiphyseal ossification:

Answer 12

 Ends of bone form spongy bone

 Articular cartilage on end of bone – growth/epiphyseal plate on other side

Question 13

• Collagen:

structure + synthesis

Answer 13

o Structure – 3 collagen molecules -> tropocollagen -> collagen fibril
o Hydroxypoline holds together 3 collagen molecules – assisted by vitamin C
o Synthesis – collagen molecules inside cell -> tropocollagen outside cell

Question 14

(^) Types of collagen

Answer 14

I - skin
II - cartilage
III - liver, bone, spleen (reticulum)
IV - basement membrane
V - placenta

Question 15

• Calcium function and distribution:

Answer 15

o	Skeletal calcium – 1200g
o	Extracellular calcium – 1g
o	Functions:
	Normal blood clotting
	Muscle and nerve function
o	Blood distribution:
	Over half protein bound/complexed – not useable
	Under half ionised – useable
	Alkalosis causes more protein bound calcium – ALBUMIN

Question 16

• Calcium kinetics:

3 of them

Answer 16

o Gut – absorption in, faecal Ca out
o Kidney – reabsorption in, excretion out
o Bones – resorption in, formation out

Question 17

Ca absorption in the gut %%%%%

Answer 17

o Gut:
 Actively absorbed in duodenum and jejunum
 Passively absorbed in ileum and colon

Question 18

Ca absorption in the kidney %%%%%

Answer 18

 Majority passively reabsorbed in PCT and ascending loop

 Minority actively reabsorbed in DCT – under hormonal control

Question 19

• Calcium and phosphate regulation:

Answer 19

o Parathyroid hormone:
 Secreted by chief cells in 4 parathyroid glands
 Chief cells detect low serum calcium with Ca surface receptors
 Calcitriol regulates PTH – binds to vit D nucleus receptor
 Kidney actions:
• Increased calcium reabsorption in DCT
• Decreases phosphate reabsorption in PCT
• Increases 1,25 (OH)2 vit D metabolism
 Bone actions:
• Increases osteoclast activity, decreases osteoblast activity
• More Ca from bone degradation

Question 20

o Calcitriol:

Answer 20

 Skin – 7-dehydrocholesterol -> vitamin D (via UV)
 Liver – vitamin D -> 25-hydroxyvitamin D (not metabolically active)
 Kidney – 25-hydroxyvitamin D -> 1,25-dihydroxyvitamin D (active)
 High serum PTH/low serum calcium = more 1,25-OH vit D produced
 Stimulates increased Ca and phosphate absorption in gut

Question 21

-Phosphate

Answer 21

 FGF23 major regulator of phosphate metabolism
 Produced by osteocytes in response to increased phosphate levels, PTH and 1,25-OH vit D
 Decreases proximal tube reabsorption of phosphate and gut reabsorption of phosphate