Calcuim and Phosphate metabolism Flashcards
What is the distribution of calcium in the body?
- 1st largest pool- ~90% calcium in bone in form of hydroxyapatite crystals.
- 2nd largest pool : intracellular calcium mitochondria and ER
- Smallest pool : ECF (interstitial calcium and blood calcium.
What are the two primary calcium channels in the cell membrane and their controls?
- Voltage gated channels: Muscles and nerve cells. These are controlled by electric membrane potential.
- Ligand Gated channels: When ligand binds to receptor it opens channel. Most cells have this and is controlled by hormones and neurotransmitters.
How is calcium absorbed in the intestine?
absorption occurs by either passive diffusion: If there is high calcium content in the lumen. Or active transport when there is low calcium in the lumen. This is regulated by vitamin D.
How is calcium reabsorbed in the kidney?
• Ca++ reabsorbed at proximal tubules, then distal tubules then ascending loop of henlee.
What is the calcium distribution in the bone?
• soluble portion of bone ( amorphous crystal and soluble calcium) which is between osteoblasts and osteocytes.
What are the cell types in the parathyroid gland?
◦ Chief cells create PTH
◦ Oxyphil cells: Fxn’s unknown
How do the Chief cells in the parathyroid gland sense calcium and magnesium levels to initiate the synthesis and release of PTH?
• Chief cells have a calcium sensor which, when decrease is detected it will cause release of PTH
What is the overall effect of PTH on calcium and phosphate metabolism?
Effect of PTH is to increase calcium and decrease phosphate.
What are the effects of PTH on amorphous bones?
◦ Transfer calcium across the osteoblast-osteocyte membrane
◦ No effects of phosphate concentrations in the blood
What are the effects of PTH on stable bones?
- PTH stimulates osteoblasts to secrete receptor activator of nuclear factor kappa b ligand ( RANK or RANK L). RANK L will activate Osteoclast precursor, which will create an active osteoclast.
- This will also cause inhibition of OPG or osteoprogesterin, which competes to bind with ligand, and will decrease the creation of osteoclasts.
What are the effects of PTH in the kidney?
- PTH will decrease Phosphate reabsorption in the proximal convoluted tubules.
- Ca++ reabsorption increases in the distal convoluted tubules.
How does PTH regulate the synthesis of the active vitamin D?
- PTH can promote the fxn of 1a - hydroxylase which will produce calcitriol. This will also be the reason 24-hydroxylase is produced which can also be formed because of high serum phosphate. The result is 24-25 (OH)2 D (inactive)
- 24- hydroxylase inactivates 1,25 (OH)2 D.
- feedback regulations. ***
How does the active vitamin D regulate calcium and phosphate metabolism?
1.) Ca++ absorption in intestine
2.) Ca++ absorption in kidney
3.) Ca++ and phosphate release in bone.
All will result in increase in calcium
What are the primary functions of calcitonin?
- Calcitonin counteracts the fxns of vitamin D and PTH.
- Inhibits osteoclasts and stimulates osteoblasts- decrease in mvmt of ca++ from labile bone calcium pool to the ECF.
- Inhibits Ca2+ absorption in the GI,
- Increases renal excretion of calcium and phosphate.
- This can lead to hypocalcemia and hyphosphatemia.
How does too much blood transfusion cause hypocalcemia?
When given too much blood (i.e transfusion) the blood product will have too much citrate and EDTA which can chelate Ca++ (or make it form a complex that is not absorbable
