Calcium and Phosphate Regulation Flashcards
What three hormones regulate calcium and phosphate levels?
Parathyroid hormone (PTH), vitamin D (calcitriol), and calcitonin.
Which gland secretes parathyroid hormone?
The parathyroid glands.
What organ produces calcitonin?
The thyroid gland.
Where is vitamin D first synthesized?
In the skin from 7-dehydrocholesterol upon exposure to sunlight.
What organ converts vitamin D to its active form?
The kidneys.
What stimulates PTH release?
Low plasma calcium levels.
What is the effect of PTH on bone?
Stimulates bone resorption to release calcium and phosphate.
What enzyme does PTH activate in the kidneys?
1-alpha hydroxylase.
What does 1-alpha hydroxylase do?
Converts calcidiol to calcitriol (active vitamin D).
What part of the nephron does PTH act on?
The distal convoluted tubule.
What is the role of calcitriol in the gut?
Increases absorption of calcium and phosphate.
What is the feedback effect of calcitriol on PTH?
It inhibits PTH secretion.
Where is calcidiol (25-hydroxyvitamin D) formed?
In the liver.
What is the active form of vitamin D called?
Calcitriol (1,25-dihydroxy vitamin D3).
What triggers calcitonin release?
High plasma calcium levels.
What is the main function of calcitonin?
Lowers plasma calcium levels.
Does calcitonin play a major role in humans?
No, its role is minor compared to PTH.
What do osteoblasts do?
Build bone by producing collagen and minerals.
What do osteoclasts do?
Break down bone and release calcium and phosphate.
What receptor do osteoclast precursors express?
RANK receptor.
What does RANK ligand do?
Binds to RANK to activate osteoclasts.
What does OPG do?
Inhibits RANK ligand from activating osteoclasts.
How does PTH affect OPG production?
It inhibits OPG to promote osteoclast activation.
What role does M-CSF play in bone resorption?
Stimulates osteoclast proliferation and differentiation.
