Vitamin D

Question 1

Types of Vitamin D

Answer 1

Dietary forms:

1. ) ergocalciferol (vitD2 from plants)
2. ) Cholecalciferol (vitD3), made by the skin from cholestrol through the action of UVB

Calcitriol - active metabolite made in the kidney

Question 2

Good sources of vitamin D?

Answer 2

fatty fish, liver, egg yolk. Not milk unless it is fortified.

Question 3

How is active vitamin D formed?

Answer 3

It is formed by successive hydroxylation of vitamin D3, (1) cholecalciferol:
First in the liver to make (2) calcidol and then in the kidneys to make (3) calcitriol - active form which is also known as 1,25 dihydroxy vitamin D3.

Question 4

Roles of Vitamin D?

Answer 4

Main role: regulates calcium absorption adn the balance between blood and bones

Role 2: it is a steroid hormone in which it binds to a neclear receptor protein, forms a heterodimer with the vitamin A receptor and then it increases the expression of calcium binding protein genes.

Role 3: achieves maintanence of calcium plasma concentration through 3 ways: 1.) increased intestinal absorption, 2.) reduced excretion (stimulating reabsorption in distal renal tubules of kidneys), 3.) mobilisation of bone mineral

Role 4: maintain normal function of the parathyroid gland and the immune system.

Question 5

Vitamin D Deficiency

Answer 5

Since its main role is to regulate calcium absorption and the balance between bones and blood. It is also a steroid hormone. A deficiency of it results in the net loss of calcium (soft bones).

1. ) rickets - insufficient mineralisation of bones and tooth matrix in children
2. ) Osteomalacia - demineralisation of adult bones. Those at risk are population that are underexposed to the sun.

Question 6

Vitamin D toxicity if their is excess consumption

Answer 6

causes calcification in soft tissue and it is impossible to get through sun exposure.