Parathyroid hormones

Source of secretion:

Parathyroid hormone (PTH) is secreted by the chief cells of parathyroid glands.

Chemistry:

It is a protein hormone having 84 amino acids and has molecular weight of 9500.

Metabolic role:

The main role of the PTH is to maintain blood calcium level. It also controls the blood phosphate level.

1. Effect on blood calcium level:

• The main action of PTH is to maintain blood calcium level by:

1. Increasing the reabsorption of calcium from the bones.
2. Increasing the reabsorption of calcium from renal tubules.
3. Increasing the absorption of calcium from the GI tract.

2. Effect on blood phosphate level:

• PTH decreases blood level of phosphate by stimulating the urinary excretion.

3. PTH also helps in the activation of Vitamin D. It does so by converting 25-hydroxycholecalciferol to 1, 25 dihydroxy cholecalciferol (calcitriol).