disorders of calcium and bone metabolism (see yr1)

Question 1

Ca2+ / PTH relationship

Answer 1

high Ca2+ plasma levels = decreased PTH
low Ca2+ plasma levels = increased PTH release

Question 2

action of PTH (4)

Answer 2

1. bone - activates osteoclasts => calcium and HPO42- released
2. intestines - absorption of calcium increased
3. kidneys (Calcium) - PTH binds to a specialized receptor on the surface of distal tubule cells, which triggers an intracellular signalling pathway that ends up increasing calcium reabsorption (i.e. less clacium secreted)
4. kidneys (phosphate) - inhibits the sodium-phosphate cotransporter in the PCT, decreasing phosphate reabsorption, and increasing urinary excretion of phosphate

Question 3

what molecules regulate calcium homeostasis (3)

Answer 3

1. PTH
2. calcitonin
3. vitamin D

Question 4

role of calcitonin in calcium homeostasis (2)

Answer 4

1. decreases plasma calcium levels
2. increases renal calcium excretion

Question 5

role of vit D in calcium homeostasis

Answer 5

promotes calcium absorption in the gut => it increases plasma levels of calcium

Question 6

ultimate effects of PTH on calcium and phosphate levels

Answer 6

increases serum calcium and decreases serum phosphate

Question 7

what does high Ca, low PTH indicate

Answer 7

other causes e.g. malignancy, sarcoidosis, throtoxicosis, berilyosis

Question 8

what does high CA, normal/raised PTH indicate (2)

Answer 8

1. if Ca:Cr ratio <0.01 then familial benign hypercalcaemia (usually FH aswel)
2. if Ca:Cr ratio >0.01 the primary hyperparathyroidism

Question 9

what is a complication of a parathyroidectoy

Answer 9

loss of voice - recurrent laryngeal nerve is easy to damage during surgery leading to vocal chord paralysis

Question 10

if Ca2+ levels and phosphate levels are deranged in the same direction what does this indicate

Answer 10

Vit D problem

Question 11

if Ca2+ levels and phosphate levels are deranged in opposite directions what does this indicate

Answer 11

PTH problem

Question 12

osteomalacia vs osteoporosis

Answer 12

osteomalacia - “soft bones”, a metabolic bone disease in which there is inadequate mineralisation of the bony osteoid due to vitaminD deficency
osteoporosis - inappropriate osteoclast:osteoblast ratio leading to decreased bone density due to high resorption rate

Question 13

osteromalacia presentation (4)

Answer 13

see yr1 DM
1. bone pain
2. myopathy
3. looser’s zone (pseudo fractures)
4. abnormal biochemistry

Question 14

rickets presentation (4)

Answer 14

1. bowed legs
2. costrochondral swelling
3. widened epiphyses at wrists
4. myopathy

Question 15

what sign might be seen on imaging of an osteoporotic vertebral fracture

Answer 15

winking owl sign (axial view)

Question 16

osteoprosis mgx (6)

Answer 16

1. conservative (exercise, smoking alcohol, diet, weight loss)
2. bisphosphonates
3. vit D/Ca
4. denosumab
5. PTH derivative
6. HRT - oestrogens (may increase risk of VTE and breast cancers tho)

Question 17

Ca, Phosphate, PTH, ALP, vit D levels in primary hyperparathyroidism

Answer 17

Ca - high
phosphate - low
PTH - high
ALP - high/normal
vit D - normal

Question 18

Ca, Phosphate, PTH, ALP, vit D levels in osteomalacia

Answer 18

Ca - low/normal
phosphate - low
PTH - high
ALP - high
vit D - low

Question 19

what is corrected serum calcium

Answer 19

Serum calcium must be ‘corrected’ with reference to albumin levels - The proportion of extracellular calcium that is ionised or ‘free’ is dependent on the amount bound to albumin

Question 20

what factor affects Ca-albumin binding levels

Answer 20

pH - Acidosis leads to a decrease in calcium binding with albumin and alkalosis an increase