Parathyroid physiology

Question 1

1. Describe the physiological roles for calcium and phosphate.

Answer 1

Calcium

• structural->bone
• 2nd messenger
• ca2+ dependent exocytosis
• Excitability–> decreased Ca2+= increased excitability
• —due to charge screening and perceived potential

Phosphate

• structural-> bone
• energy storage/currency
• essential component of RNA and DNA
• regulation of cellular systems through phosphorylation

Question 2

2. Illustrate the various compartments involved in calcium and phophate homeostasis and identify the mechanisms for distribution of calcium and phosphate between plasma and the bone.

Answer 2

Gut, Feces, Kidney, Urine, Bone

Blood- 8-10 mg/dL, 50 % is bound to albumins, 10 % as a salt, 40% free

osteocytic process-net exchange of 10 grams of calcium per day

osteoclastic property–> slow, net exchange of 280 mg/day of both calcium and phosphate

Question 3

3. Describe the regulation of PTH release.

Answer 3

peptide hormone, calcium dependent exocytosis from chief cells in para thyoid gland

• -when calcium gets low, parathyroid goes high
• there is a calcium sensor (Gq) on the cell surface. when receptor is not bound, PTH released

Question 4

4. List the actions of PTH.

Answer 4

excretes phosphate in the urine

holds onto calcium in the kidney

increases the hydroxylation of vit D3 to absorb calcium from gut

Question 5

5. Diagram the steps of Vitamin D synthesis and their regulation.

Answer 5

Vit D3 is produced in the skin or absorbed in the gut. In the liver it is hydroxylated to 25-OH-D3 in th eliver, its then hydroxylated again to 1,25-(OH)2-D3 (active form) in the kidney or deactivated into 24,25-(OH)2-D3 in the kidney

Question 6

6. List the actions of Vitamin D.

Answer 6

promotes gut absopriton of calcium by increasing calbindin on all cells in the intestinal wall

Question 7

what is normal serum calcium

what is normal serum phosphate

Answer 7

8-10 mg/dL

3-6 mg/dL

Question 8

how much calcium is bound to albumins?

Answer 8

50%

Question 9

what is net change of osteocytic process per day?

what is net change of osteoclastic process per day?

Answer 9

10 grams of calcium only

280 mg of both calcium and phophate

Question 10

what is psuedo hyperparathyoidism?

Answer 10

PTH receptors dont work