What three hormones regulate body Ca2+ levels?
- Vitamin D
Parathyroid gland chief cell release of PTH is regulated by a ____________.
Ca-sensing receptor (CaSR)
NOTE: Active Vitamin D3 supresses PTH synthesis and stimulates CaSR synthesis. CaSR inhibits PTH. PTH blockage occurs in two places. It block the gene from being transcibed and its released from stored vesicles is also blocked when calcium is high.
What effect does PTH have on bone?
- Stimulates bone osteoblasts to increase growth and metabolic activity
- Stimulates bone resorption and releases calcium and phosphate into blood
What effect does PTH have on the kidneys?
- Increases calcium reabsorption and reduces reabsorption of phosphate
- Stimulates synthesis of Vitamin D3
- Inhibits resorption of Na+ and bicarbonate in the proximal tubule and stimulates a Na+-H+ exhanger
NOTE: The kidneys are the only place we can really make adjustment in the levels of calcium and phosphate
What effect does PTH have on the intestine?
Increases calcium and phosphate reabsorption via vitamin D
In osteons, there is a ________ where blood vessels are coming in.
Osteocytes make contact with the cytoplasmic processes of their counterparts via a network of small transverse canals, or ________.
Describe the fast exhange of bone Ca2+
- Moved from the labile pool (in canaliculi) in the bone fluid into the plasma by means of PTH-activated Ca2+ pumps located in the osteocytic-osteoblastic bone membrane
Describe the slow exchange of bone Ca2+
- Ca 2+ is moved from the stable pool in the mineralized bone into the plasma by means of PTH-induced dissolution of bone (via osteoclasts)
Which cells secrete calcitonin?
Parafollicular (C cells) of the thyroid gland
*It is synthesized as the preprohormone and released in response to high plasma calcium
NOTE: Parathyroid hormone pretty much maintains physiological balance. If we ger really far out of the physiological range and have high high levels of calcium then calcitonin will respond.
Feedback regulation of the Synthesis and Secretion of PTH & Calcitonin
What is the principal action of Vitamin D?
Increased intestinal absorption of Ca2+ and (PO4)3-
Which enzyme is required to create the active form of Vitamin D?
*1-alpha-hyroxylase is stimulated by PTH and suppressed by Vitamin D
What effect does Vitamin D3 have on plasma phosphate levels?
It increases (PO4)3- levels
PTH acts __________ (indirectly/directly) on the intestine.
What effect does a decrease in plasma phosphate have on PTH levels?
A decrease in in plasma phosphate leads to an increase in plasma calcium, which would lead to a decrease in PTH.
NOTE: A decrease in plasma phosphate also leads to an increase in Vitamin D3.
Primary hyperparathyroidism causes:
- Kidney stones
Secondary hyperparathyroidism causes:
- Slowly developing renal failure generated by hyperphosphospahtemia and hypocalcemia
- Accelerated bone resorption
Symptoms of hypoparathyroidism