Calcium homeostasis & vitamin D

Question 1

How is vitamin D converted to its active form in the body?

Answer 1

UVB rays in sunlight convert cholesterol in skin to vitamin D

Some is ingested in the diet (oily fish)

Processed by liver

Processed by kidney to form active form 1,25-dihydroxyvitamin D

Question 2

What is the active form of vitamin D?

Answer 2

1,25-dihydroxyvitamin D

Question 3

What does vitamin D do it the body?

Answer 3

Increases calcium and phosphorous absorption in gut, and reabsorption in kidney

Retains Ca and P in the body

Question 4

What hormone is secreted when serum calcium levels are low. Where is it released from?

Answer 4

Parathyroid hormone

From the parathyroid glands

Question 5

What does parathyroid hormone do?

Answer 5

Increases serum calcium

Question 6

How does parathyroid hormone increase serum calcium?

Answer 6

REABSORPTION
of calcium in the DCT of the kidney nephrons

ABSORPTION
active absorption in duodenum & jejunum (controlled by vit D)

RESORPTION
rapid release via calcium on bone surface
or
increased osteoclast action provides a slower release of calcium

Question 7

What hormone is secreted when serum calcium levels are too high. Where is it released from?

Answer 7

Calcitonin

From C-cells of thyroid gland

Question 8

What does calcitonin do?

Answer 8

Decreases serum calcium

Question 9

How does calcitonin decrease serum calcium?

Answer 9

Decreases bone resorption