Lecture 22: Ca metabolism Flashcards
What regualtes Ca concentrations:
Ca, Vit D and PTH are responsible for Ca homeostasis
What are the main organs involved in Ca homeostasis:
Intestine
Kidneys
Bones (stores)
How is Ca found?
iCa - 50%
Protein bound - 40%
Ion-complexed - 10%
Write an overview on PTH:
- Chief cells of parathyroid gland
- Released within minutes of decreased Ca
- Main defender of the serum Ca
How does PTH act?
- Stimulates osteoclastic bone resorption
- Stimulates renal tubular reabsorption of Ca2+
- Stimulates renal 1-hydroxylation of 25(OH)D
Restores serum Ca by acting on all effector organs. Bone and kidney directly; Intestine indirectly
Insert the diagram
Slides 2-3
insert slide five
thanks
What regulates PTH?
- Serum ionized Ca (most imp) (decreases PTH)
- Serum phosphate (increases PTH)
- Serum 1,25 dihydroxyvitamin D (decreases PTH)
Describe how ECF Ca is found:
45-50% ionized, bioactive
5-10% complexed with anions i.e HCO3
45-50% protein-bound, albumin and globulins
Describe how Ca can induce PTH release:
Ca binds the receptor with Mg as a cofactor to decreased PTH released from cheif cells
How does CaR regulate renal tubular Ca handling:
Ca binds CaR and decreases the absorption via:
- Paracellularly
- Na,Cl,K pumps and K efflux pumps (i.e the gradients that create the gradient for Ca paracellular transport)
Describe Vit D metabolism:
slide 10
Does calcitonin regulate serum Ca?
no
What is PTHrP?
PTH related peptide
- Important paracrine regulator of breast, skin and bone development.
- Not a physiological regulator of serum Ca BUT in excess acts same was as PTH and can cause hypercalcemia
What are the PTH-dependent causes of hypercalcemia?
Primary hyperparathyroidism
FHH/Inactivating CaSR mutations