Ca homeostasis Flashcards
How is there a substantial gradient for Ca to move it into the cytoplasm?
-Bulk of intracellular is sequestered in organellar compartments. Free Ca in the cytosol is much lower
What are virtual efflux mechanisms?
Regulate the Ca rise in cells by Na/Ca exchanger and Ca pumps
What percentage of Ca is filtered at the glomerulus?
60% the rest is bound to proteins
What amount of filtered Ca is reabsorbed?
98-99%
Does the kidney secrete Ca?
No
Describe the paracellular Ca absorption in the PT?
Na is reabsorbed through transcellular reabsorption and this concentrates Ca. The Ca then goes across the tight junctions similar to Cl
How is Ca absorbed in the DT?
This is transcellular. Ca enters through ion channel (ECaC) and binds to calbindin which releases it at the basolateral membrane. Ca exits across the basolateral membrane through Na/Ca exchangers and Ca pumps
What is a reservoir for Ca?
Bone
What is the effect of PTH on bone?
Bone to plasma Ca distribution and bone resorption
What is effect of PTH on kidney?
Enhance reabsorption of Ca and Vitamin D activation
What inhibits PTH when there is high Ca levels?
CaSR
What effect does PTH have on ECaC?
Increases the gating of Ca through adenylate cyclase and phospholipase C pathways
What is the effect of Thiazide diuretics on Ca absorption?
Thiazide inhibits the NaCl cotransporters so there is a greater Na gradient which Ca depends on. This means it is more available for Ca absorption
What are the sources of Vitamin D?
- UV stimulates production by the skin
- Ingest from food
Where is the first hydroxylation of Vitamin D?
Liver
