Ca Homeostasis

Question 1

What does Ca regulate in the body?

Answer 1

1. neuromuscular transmission-movement/breathing
2. uterine smooth muscle contraction
3. arterial smooth muscle contraction
4. cardiac contraction- BP
5. bone development-growth
6. delivery of infant, milk ejection, menstruation

Question 2

What controls Ca regulation?

Answer 2

1. hormones, PTH
2. calcitonin, vit D
3. phosphates
4. osteoblasts/osteoclasts
5. age
6. diet
7. drugs
8. disease

Question 3

Where does PTH directly affect Ca?

Answer 3

1. bone
2. kidney

Question 4

Where does PTH indirectly affect Ca?

Answer 4

intestine

Question 5

What effects does PTH have on the bone?

Answer 5

1. increase Ca by activation of osteoclasts chipping away outer layer of bone to release Ca into the blood
2. modulates osteoblasts and increases total number of osteoblasts
3. stimulates cAMP production in osteoblasts

Question 6

What effects does PTH have on the intestine?

Answer 6

regulates Ca absorption through the intestine via formation of calcitriol in the kidneys

Question 7

How does PTH affect the kidneys?

Answer 7

1. promotes Ca reabsorption (decrease excretion) through the distal convoluted tubules of the nephron through trp Vanilloid type V Ca channels
2. prevents phosphate reabsorption (increase excretion) in the proximal convoluted tubule by down-reg of Na-dependent phosphate transporter

Question 8

Which form of vit D increases absorption of Ca into the body through the intestine?

Answer 8

1,25-diOH Vitamin D3 (CALTIRIOL)

Question 9

How does calcitriol increase absorption of Ca?

Answer 9

1. calcitriol complexes with the vit D3 receptor in the nucleus and binds to the Vitamin D Response Element (VDREs) located on specific genes
2. the result is inhibition or activation of these genes (ex. activation of Ca/PO4 co transporter gene –> upregulation of Ca/PO4 co transporters in the intestine –> increased absorption of Ca