Maintenance of Calcium balance

Parathormone,Vit D and Calcitonin act together to maintain calcium homeostasis.

Parathormone(PTH)

Secreted when serum calcium falls.

Increase calcium levels by:

  1. Promoting bone resorption
  2. Increased calcium absorption from intestine(via vit D)
  3. Increased reabsorption of Calcium from renal tubules.(Phoshate reabsorption reduced)

Overall effect: Increase S.Ca2+, decrease S.Phosphate.

Vitamin D

Stimulus of secretion: Decreased S.Ca2+,decreased S.PO4-,Increased PTH.

Acts by:

  1. Promoting bone resorption.
  2. Increased PO4- and Ca2+ absorption from intestine
  3. Increased Ca2+ and PO4- reabsorption from renal tubules.

Overall effect:Increase both S.Ca2+ and S.PO4-

Calcitonin

  1. Stimulated by increased S.Ca2+
  2. Acts by a single mechanism: Decrease bone resorption

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