Zheng RS 2- Parathyroid Hormone Physiology

Question 1

What cells secrete PTH?

Answer 1

Chief cells

Question 2

How does the parathyroid gland know when to secrete PTH? What is the main inhibitor of this secretion?

Answer 2

Calcium sensing receptor, which is also on C-cells.

Calcium is the main inhibitor of PTH secretion

Question 3

What is the half-life of PTH?

Answer 3

Around 4 minutes

Question 4

What receptor does PTH bind to? Where is this receptor most abundant?

Answer 4

PTH1R, a GPCR that is most abundant on bone and kidney

Question 5

What is the mechanism for PTH’s 2 functions on the kidneys?

Answer 5

PTH limits calcium excretion in the kidneys by inserting apical calcium channels in the distal tubular cells

In the proximal tubular cells, PTH stimulates the degradation of Na/Pi cotransporters, inhibiting phosphate reabsorption

Question 6

What effect does PTH have on vitamin D?

Answer 6

PTH will upregulate the activity of 1a-hydroxylase, which converts vitamin D from a metabolite to its active form.

Question 7

What effect does PTH have on the intestine? What is the mechanism for how to accomplishes this?

Answer 7

By activating vitamin D, PTH indirectly leads to the absorption of calcium form the intestine.

It will stimulate the expression of calcium channels, calcium pumps and calbindin

Calcium will enter the cells via calcium channels, bind to many proteins including calbindin, and be transported across the basolateral membrane via Ca2+ pumps and a Na/Ca2+ cotransporter

Question 8

What causes familial hypocalciuric hypercalcemia?

Answer 8

A mutation of the calcium-sensing receptor