Question

Parathormone influences calcium absorption in the small intestine by regulating the metabolism of
(a) Vitamin C
(b) Vitamin D
(c) Vitamin B
(d) Enterogastrone

Answer 1

Hint: Parathormone regulates the metabolism of fat- soluble substance which contains the steroid nucleus with cyclopentanoperhydrophenanthrene ring. Its deficiency causes rickets. Its production in the skin is directly proportional to the exposure to sunlight and inversely proportional to the pigmentation of the skin.

Complete step by step answer:
Parathyroid hormone regulates calcium levels within the blood, largely by increasing the amount once they are too low. It does this action through its actions on the kidneys, bones and intestine:
Bones – parathormone stimulates the discharge of calcium from large calcium stores within the bones into the bloodstream. This increases bone destruction and reduces the formation of the latest bone.
Kidneys – parathyroid hormone reduces the loss of calcium in the urine. Parathyroid hormone also stimulates the assembly of active vitamin D within the kidneys.
Intestine – parathyroid hormone indirectly increases calcium absorption from food in the intestine, by the effects of vitamin- D metabolism.
So, the right answer is, ‘Vitamin D.’

Additional information:
- The decrease in calcium ion concentration within the extracellular fluid causes the parathyroid glands to increase their rate of secretion within minutes.
- The increase in plasma calcium concentration of about 10 per cent causes a moment twofold or more increase within the speed of secretion of calcitonin, which is shown by the blue line.
- The primary stimulus for calcitonin secretion is increased plasma factor IV concentration.
- Control of Parathyroid Secretion by:
Calcium Ion Concentration
Conditions causing enlarged parathyroid
Rickets
Pregnancy
Lactation

- Conditions causing reduced sized parathyroid
Excess calcium in diet Increased vitamin D in the diet
Bone absorption caused by factors aside from PTH

Note:
- Parathormone provides a strong mechanism for monitoring the extracellular calcium and phosphate ion concentrations present in the blood by regulating intestinal reabsorption, renal excretion exchange. Thus, helps in controlling the calcium and phosphate ion concentration.
- Parathyroid hormone synthesized within the type of a preprohormone, which then cleaved to a prohormone then to the hormone itself which consist chain of 84 amino acids by the endoplasmic reticulum and Golgi body packaged in small vesicles from where they are transported to target site.