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Parathyroid Gland (parathyroid hormone (regulation (stimulatory (decrease…
Parathyroid Gland
parathyroid hormone
secreted by chief cells
target: bone and kidney
principal regulatory of Ca homeostasis
increases blood Ca conc
stimulates movement of Ca and P from bone
increases renal phosphate clearance
increases Ca reabsorption in the kidney
stimulates production of active form of Vit D (aka calcitrol - also regulator of Ca)
regulation
stimulatory
decrease in blood Ca (EC ionized Ca)
for min to min control
calcitrol/Vit D (long term balance)
phosphate ions
inhibitory
increase in blood Ca
vitamin D
group of steroid molecules
essential for bone health
promotes mineralization of new bone
increases absorption of Ca from SI
promotes Ca and P reabsorption in the kidney
Vit D3 (cholecalciferol)
generated by skin when light E is absorbed
must be metabolized in the body to hormonally active form
Calcitrol (hormonally active form)
synthesis
cholecalciferol hydroxylated to 25-hydroxycholecalciferol
25-Vit D is substrate for 1-alpha-hydroxylase
produces calcitrol
regulation
production of 1-alpha-hydroxylase is tightly regulated
parathyroid hormone-related protein
secreted by certain tumors
causes hypercalcemia
stimulates resorption of Ca from bone
suppresses Ca loss in urine
regulate pancreatic beta islet cell mass
secreted by smooth muscle in response to stretch
causes relaxation and vasodilation
normal expression is critical in development of bones, teeth, cartilage, and mammary glands
calcitonin
(thyroid hormone)
produced by C cell in the thyroid (parafollicular cells)
stimulated by increased blood Ca
reduce blood calcium levels
suppress renal reabsorption of Ca
inhibits bone resorption (breakdown)