Vitamin D/Calcium

Question 1

Vitamin D is converted to what in the liver?

Answer 1

25 Hydroxyvitamin D

Question 2

25 hydroxy vit D is converted to what in the kidneys?

Answer 2

1,25 hydroxyvitamin D

Question 3

What catalyses conversion of 25-hydroxyvit D in the kidneys?

Answer 3

1-alpha-hydroxylase

Question 4

What three actions does 1,25-hydroxyvitamin D cause?

Answer 4

1. Increased Ca & PO4 absorption in the GIT
2. Inc Ca absorption from the DCT in the kidney
3. Inc PO4 absorption from the PCT in kidney

Question 5

What are the biochemical abnormalities found in vitamin D deficiency?
(Vit D, PO4, Ca, PTH)

Answer 5

Decreased vitamin D
Decreased PO4
Decreased Ca
Increased PTH

Question 6

Biochemical abnormalities found in hypophosphatemic rickets?

Answer 6

Decreased PO4
Normal Ca
Normal PTH
High urinary PO4

Question 7

What does PTH do re: Ca/PO4;
Gut
Bone
Kidney

Answer 7

Gut: Increases reabsorption of Ca & PO4
Bone: Increases bone resorption
Kidney: inc Ca resorption, stimulates PO4 excretion

Question 8

What does Vitamin D do to Ca & PO4 in;
Bone
Gut
Kidney?

Answer 8

Bone: Increase reabsorption of Ca & PO4
Gut: Increase reabsorption of Ca & PO4
Kidneys: Inc Ca & PO4 reabsorption

Question 9

Parathyroid senses what type of Ca?

Answer 9

ionised Calcium

Question 10

What percentage of Calcium is ionised?

Answer 10

45% of total calcium

Question 11

Signs of Rickets on x-ray?

Answer 11

Splaying
Cupping
Fraying
Best seen on distal ulnar and knees

Question 12

Causes of hypercalcaemia? (Hi5s)

Answer 12

Hyperparathyroidism (familial, isolated, syndromic)
Idiopathic (William’s)
Infantile (fat necrosis, maternal hypoparathyroidism)
Infection (TB)
Infiltration (cancer, sarcoidosis)
Ingestions (milk-alkali syndrome, thiazide diuretics, vit A tox, Vit D tox)
Skeletal disorder (hypophosphatemia, immobilisation, skeletal dysplasia)