OP Part A Khan Study Guide Answers

What is hydroxyapatite?

storage of calcium / skeleton form/ basically our bones

What are the normal functions of osteoblasts and osteoclasts?

osteoblasts- bone formation

osteoclasts- bone resorption

Discuss phosphate:

a) functions

b) absorption

Functions- regulate kinases, bone structure, energy

Absorption- through the intestines by passive diffusion

Discuss calcium metabolism

Absorbed in intestines, then travels to bone, filtered and reasborped in the kidney, then excereted by the kidneys

Differentiate sources of Vit D2 and Vit D3

Vit D2- PLANTS

Vit D3- ANIMALS, or by UV Light

Do Vit D2 and Vit D3 have different biological properties?

NO

What is the precursor of Vit D in the skin

7- dehydrocholesterol

Distinguish Ergocalciferol side chain

Distinguish Cholecalciferol side chain

Details of 1st hydroxylation to form calcitriol

For the 1st hydroxylation we either take Cholecalciferol or Ergocalciferol and add an -OH group on position 25 to form 25-hydroxycholecalciferol. This takes place in the liver.

Details of 2nd hydroxylation to form calcitriol

For the 2nd hydroxylation we take the 25-hydroxycholecalciferol and add an -OH group to position one to form calcitriol. This takes place in the kidneys.

Which hydroxylation is hormone dependent/independent?

1st hydroxylation- hormone INDEPENDENT

2nd hydroxylation- hormone DEPENDENT

Know effects of Vit D on:

• kidney

• bone secretion

• intestine

kidney- increase Ca and P reabsorption

bone secretion- increase osteoclast activity

intestine- increase Ca and P absorption

Regulation of PTH secretion by Vit D

• Basically Vit D turns off PTH

• More specifically: Vit D binds to nuclear receptors in PTH gland and inhibits PTh synthesis and release

Receptor activation of Vit D

• Vitamin D receptor is a nuclear receptor not located in the nucleus, but travels to the nucleus (if that makes sense)

How is PTH secretion regulated by Ca levels?

High Ca= Inhibit PTH secretion

Low Ca= activate PTH secretion

Discuss PTH’s effect on the kidney

• increase Ca reabsorption

• decrease P reabsorption

NOTE: opposite of Vit D

Discuss PTH’s catabolic effect on bone

Path: PTH—> PTH receptor (osteoblast) —> RANKL→ RANK→ Osteoclast precursor->osteoclast

• we stimulate osteoclasts to resorb bone

Discuss PTH’s anabolic effect on bone

• stimulate osteoblast maturation

• inhibit osteoblast cell death

• release growth factors from osteoblasts

Discuss PTH’s effect on the intestine

• increase calcium absorption

• increase phosphorus absorption

Which gland is calcitonin secreted from?

Thyroid

Is the total sequence of AA needed for calcitonin?

YES

What are triggers for calcitonin release?

• increase serum Ca

What are calcitonin’s effects?

• directly inhibits bone resorption

• inhibits Ca and P reabsorption from kidney

• decrease Ca absorption from GIT

What is FGF’s role in phosphate metabolism?

• promotes urinary phosphate excretion

• suppresses Vit D activation