Editing Parathyroid (section)

== '''Physiology''' ==

=== '''Control of PTH secretion''' ===

** Calcium binds to calcium-sensing receptors on the surface of the chief cells and inhibits PTH secretion and PTH gene expression
** High calcium also enhances PTH degradation
** Conversely, low calcium increases PTH secretion and expression
** The active form of vitamin D can bind to receptors on chief cells and inhibit PTH gene expression and parathyroid cell proliferation

=== '''PTH synthesis''' ===

=== '''PTH function''' ===

** Half-life of PTH is 3-5 minutes (range 1-21 minutes)
** Kidney - acts on ascending limb of the loop of Henle and distal convoluted tubule of the kidneys to enhance calcium reabsorption, inhibit phosphate reabsorption, and increase phosphate excretion causing phosphaturia. Also stimulates conversion of vitamin D to active metabolite, which then increases intestinal absorption of dietary calcium in the small intestine. Effects take minutes to hours.
** Bones - increases bone remodelling and release of calcium and phosphate from the skeleton. With chronically elevated PTH, the net effect bone resorption leading ot osteopaenia and osteoporosis. Effects take hours to days.



[[Category:Anatomy]]