Question

Compare and contrast the effects of ParaThyroid Hormone (PTH), Calcitriol (vit D3) and Calcitonin on calcium metabolism, phosphate metabolism, and bone growth. What other hormones are involved in bone growth, what bone cells are affected, and how does each type affect bone structure and growth?

Answer 1

Parathyroid Hormone (PTH)

It is the hormone which is secreted by parathyroid gland in the neck & they are four in number.its main function is to maintain blood calcium levels normal & maintaining adequate calicium levels in the body.PTH also prevent low calcium levels in the blood by acting on bones.when blood calcium levels are low, PTH releases from parathyroid gland and acts on the bones and starts resorption of bones until calcium levels in the blood becomes normal.Excess release of PTH cause continuous resorbtion of bones and leads to osteoporosis.In osteoporosis the bones become weak and lead to destruction of bones.PTH also acts on the intestine and increases the vitamin D metabolism.PTH reduces the reabsorption of phosphate from the kidney that is it helps in excretion of phosphate.PTH helps in increase the uptake of phosphorus from intestine and bones into the blood

Calcitriol(vit D3)

It is active form of vitamin D.It is also a hormone involved in absorption of calcium and phosphorus and bone growth.It helps in absorption of the intestinal calcium.calcitriol helps in patients with hyperparathyroidism, osteoporosis and it helps in strengthening the bones.Normally calcitriol is synthesized in the kidney.calcitriol increases the absorption of phosphorus.

Calcitonin

calcitonin is reduces the blood calicium and phosphorus levels.It is exactly opposite to the action of parathyroid Hormone .it reduces the calcium levels by inhibiting osteoclasts.Osteoclasts are responsible for the destruction of bone calicium.So calcitonin decrease the blood calicium levels.calcitonin prevents from osteoporosis by inhibiting osteoclasts.calcitonin carries phosphate into the bone cells and prevent calicium out of the bone into blood.it increases phosphate levels in the bone and decrease the blood phosphate.

All the calcium regulating hormones have their actions on bones growth .other hormones include androgens , estrogens helps in bone formation.