Endocrine bone disorders

Question 1

What is the make up of bone?

Answer 1

Organic: osteoid unmineralised bone
Inorganic: calcium hydroxyapatite crystals 65%mass

Question 2

What is the process of osteoclast differentiation?

Answer 2

RANKL is expressed on osteoblasts

RANK-R on osteoclast precursors bind to this and stimulates osteoclast formation

Question 3

What is an inhibitor of osteoclast formation?

Answer 3

Osteoprotegerin: decoy receptor for RANKL

Question 4

Describe the relationship between PTH and vitamin D

Answer 4

1. Increase bone reabsorption (release Ca and phosphorous)

2. Kidney is stimulated to make calcitriol -> small intestine increases absorption of dietary calcium

Question 5

What is the affect of hyper/hypocalcaemia on AP generation?

Answer 5

Hypercalcaemia: Inhibits Na+ influx, less excitability
Hypocalcaemia: Greater Na+ influx, more excitability

Question 6

What are the main signs of hypocalcaemia?

Answer 6

Paraesthesia
Convulsions
Arrythmias
Tetany

Question 7

What are the clinical tests for hypocalcaemia?

Answer 7

Chvostek’s sign: twitch on zygomatic arch

Trousseau’s sign: BP cuff causes carpopedal spasm

Question 8

Describe the synthesis of active vitamin D in the body

Answer 8

Vitamin D is synthesised in the liver
25hydroxyvitamin D
In the kidneys using 1-alpha hydroxyls -> 1, 25dihhydroxycholecalciferol