Calcium metabolism

Question 1

Name 3 Common metabolic bone disorders

Answer 1

○ Osteoporosis
○ Osteomalacia/Rickets
○ Paget’s disease

Question 2

An ___ in calcium will cause a failure of depolarisation

Answer 2

increase

Question 3

A ___ in calcium will cause a very trigger happy neurological system leading to epilepsy and fits

Answer 3

decrease

Question 4

99% of calcium stored in?

Answer 4

bone

Question 5

In what forms is calcium found most abundantly?

Answer 5

Free (ionised) - 50% - BIOLOGICALLY ACTIVE

Question 6

In what forms is calcium found?

Answer 6

1. Free (ionised) - 50%
2. Protein-bound - 40% - bound to albumin
3. Complexed - 10% - citrate/phosphate

Question 7

A patient has liver disease which calcium reading is most representative of their true calcium? why?

Answer 7

corrected calcium

low albumin can cause low total calcium reading

Question 8

free calcium is what % of total serum calcium?

Answer 8

50%

Question 9

how to calculate corrected calcium?

Answer 9

Total serum calcium + 0.02

x (40 - albumin)

Question 10

PTH obtains calcium from which THREE sources?

Answer 10

○ Bone (osteoclast activation)
○ Gut (absorption)
○ Kidneys (calcium reABsorption and renal 1a-hydroxylase activation)

Question 11

what is the role of 1a-hydroxylase in increasing calcium ?

Answer 11

it results in the production of calcitriol (1,25-dihydroxycholecalciferol) - from kidney

which helps absorb calcium from gut

Question 12

2 hormones involved in calcium homeostasis?

Answer 12

PTH

Vitamin D3 (steroid hormone) (1,25)

Question 13

25-OH vit d3 is made where?

Answer 13

liver

Question 14

calcitriol 1,25-dihydroxycholecalciferol D3 is made where?

what’s the trigger?

Answer 14

kidney

trigger - PTH

Question 15

which vitamin d3 is the only active form?

Answer 15

calcitriol 1,25-dihydroxycholecalciferol

Question 16

when you measure blood vitamin d which form is it usually?

Answer 16

25-OH D3

Question 17

which is the vitamin d from plants?

Answer 17

D2 is from plants – ergocalciferol.

Question 18

when UV hits the skin how is vitamin d made?

Answer 18

converts 7-dehydrocholesterol to

cholecalciferol (D3)

Question 19

which enzyme catalyses the conversion of cholecalciferol to 25-hydroxycholecalciferol

and where?

Answer 19

25-hydroxylase in the liver

Question 20

why can sarcoid cause high calcium?

Answer 20

1a hydroxylase expression in lung

Question 21

what do PTH and vit d do to Phosphate?

Answer 21

vit d - Increased PO4 absorbed from gut

PTH - PO4 loss in urine

Question 22

differnence between osteoporosis and osteomalacia?

Answer 22

osteoporosis - normal structure but less bone

osteomalacia - abnormal structure as low calcium due to vitamin d deficiency

Question 23

2 types vit d deficiency?

Answer 23

Childhood - Rickets

Adults - Osteomalacia

Question 24

Biochemical picture in osteomalacia?

Answer 24

□ Low Calcium
□ Low Phosphate
□ High ALP - increased resorption

§ Looser’s zones - pseudofractures

Question 25

symptoms in rickets vs osteomalacia?

Answer 25

``` Rickets § Bowed legs § Costochondral swelling § Widened epiphyses at wrists § Myopathy - no fracture risk ``` osteomalacia bone and muscle pain, fracture risk

Question 26

what is secondary hyperparathyroidism ?

Answer 26

Vitamin D deficiency which leads to osteoclasts eating up the bone to liberate calcium and normalise the plasma calcium levels

Question 27

why can kidney failure lead to osteomalacia?

Answer 27

insufficient 1a hydroxylase = vit d deficiency

Question 28

biochemical picture in osteoporosis?

Answer 28

□ Normal Calcium | □ Normal Phosphate

Question 29

where do fractures occur in osteoporosis?

Answer 29

wrist (Colle's), hip and spine

Question 30

Hyperthyroidism and Cushing's syndrome can cause osteoporosis because?

Answer 30

increased catabolism

Question 31

major cause of osteoporosis in women?

Answer 31

oestrogen loss in menopause

Question 32

treatment for osteoporosis?

Answer 32

○ Drugs: § Vitamin D § Bisphosphonates - reduce breakdown § Teriparatide (PTH derivative) - build bone § Strontium (anabolic and anti-resorptive) § HRT (oestrogens) § SERMs (e.g. raloxifene) - agonist at bone

Question 33

Mmemonic for hyperPTH hypercalcaemia?

Answer 33

BONES: path bone disease STONES MOANS: constipation, pancreatitis GROANS - psych; confusion

Question 34

patients presents with Polyuria / polydipsia Constipation Neuro – confusion / seizures / coma what do they have?

Answer 34

hypercalcaemia symptoms not unless calcium is at least 3

Question 35

patient with symptoms of hypercalcaemia what is first thing to do?

Answer 35

Is it a genuine result (repeat) total vs adjusted then measure PTH levels

Question 36

High Calcium High PTH is ?

Answer 36

primary HyperPTH

Question 37

High Calcium Normal PTH is ?

Answer 37

Cancer sarcoid Vit d overdose thyrotoxicosis

Question 38

what is PO4 in primary HyperPTH?

Answer 38

LOW

Question 39

what condition is there hypercalceamia with no symptoms? what is the aetiology?

Answer 39

familial benign hypercalcaemia, mutation in the CaSR

Question 40

most common cause of hypercalceamia?

Answer 40

primary HyperPTH

Question 41

NON PTH related hypercalcaemia. Which cancers can cause hypercalcaemia?

Answer 41

Bone metastases (eg breast Ca) small cell lung Ca - PTHrP release ``` Haematological malignancy (eg myeloma) cytokines ```

Question 42

patient taking Chlorothiazide is brought in with constipation and flank pain radiating from loin to groin. on examination he does not know the day or year. what could be the problem? how to manage?

Answer 42

He is taking Thiazide diuretics which is causing symptoms of hypercalcaemia through renal Ca2+ transport. Management; 1. Fluids+++ 2. Bisphosphonates eg zolendronic acid (if cause known to be cancer) otherwise avoid

Question 43

mechanism of hypercalcaemia of malignancy?

Answer 43

the tumours: 80% - production of PTHrp 20% - osteolytic bone mets 1% - pth producing tumours, vit d producing tumours and others

Question 44

side effects of bisphosphonates?

Answer 44

osteonecrosis of jaw and teeth acute renal failure