Vitamin D and Immune Function

Question 1

What does PTH stimulate?

Answer 1

Renal 1 alpha- hydroxylase which converts 25-hydroxycholecalciferol to 1,25 diydroxycholecalciferol which stimulates intestinal Ca++ absorption

Question 2

What is the active form of vitamin D?

Answer 2

1,25 dihydroxycholecalciferol

Question 3

What does vitamin D promote?

Answer 3

Mineralization of new bone by increasing both plasma Ca++ and phosphate so that they can be deposited in new bone mineral

Question 4

What is vitamin D responsible for in the intestines?

Answer 4

1) Increases both Ca++ and phosphate absorption

2) Induces the synthesis of calbindin D-28 K

Question 5

What is vitamin D responsible for in the kidney?

Answer 5

Increase both Ca++ and phosphate absorption

Question 6

What does PTH do in the kidney?

Answer 6

Increases Ca++ but decreases phosphate absorption

Question 7

What is vitamin D responsible for in bone?

Answer 7

Acts synergistically with PTH to stimulate osteoclast activity and bone resorption

Question 8

Why would vitamin D stimulate bone resorption?

Answer 8

Mineralized “old” bone is resorbed to provide more Ca++ and phosphate to ECF so that new bone can be mineralized (aka bone modeling)

Question 9

What does vitamin D deficiency cause in children?

Answer 9

Rickets

Question 10

What happens to the bones in a child with rickets?

Answer 10

There isn’t enough Ca++ and phosphate available to mineralize the growing bones.

Question 11

What is rickets characterized by?

Answer 11

Growth failure and skeletal deformities

Question 12

What does vitamin D deficiency cause in adults?

Answer 12

Osteomalacia

Question 13

What happens to bones in osteomalacia?

Answer 13

The new bone fails to mineralize so it softens the weight bearing bones

Question 14

How can vitamin D deficiency also play a role in hyperparathyroidism?

Answer 14

Vitamin D deficiency can lead to hypocalcemia which in turn overstimulates the parathyroid to secrete excessive PTH secondary to hypocalcemia

Question 15

What are sources of vitamin D?

Answer 15

1) Sunlight

2) Dietary sources like oily fish

Question 16

How does sunlight provide vitamin D?

Answer 16

Solar UV B penetrates the skin and converts 7-dehydrocholesterol to pre-vitamin D3 which is rapidly converted to vitamin D3

Question 17

Can you get too much vitamin D from the sun?

Answer 17

No, any excess is destroyed by the sunlight

Question 18

Besides adverse effects on bone, what other diseases are associated with vitamin D deficiency?

Answer 18

1) CV disease
2) Cancer
3) Infection
4) MS
5) Childhood asthma
6) Tuberculosis

Question 19

What cells express vitamin D receptors?

Answer 19

All cells

Question 20

What are some functions of vitamin D?

Answer 20

1) Controls over 200 genes
2) Decreases cellular proliferation
3) Potent immunomodulator
4) Control inflammation
5) Muscle strength
6) Blood pressure

Question 21

Are PTH levels high or low in chronic renal failure?

Answer 21

High (secondary response)

Question 22

Can chronic renal failure cause osteomalacia?

Answer 22

Yes, due to deficiency of vitamin D (decrease plasma Ca++, increase plasma phosphate)

Question 23

What is chronic renal failure characterized by?

Answer 23

Decrease production of 1,25-dihydroxycholecalciferol