The smallest Endocrine Gland.
The Parathyroid gland is located posteriorly in the surface of the thyroid gland. Usually, an individual has four to six of it, 8 being the greatest number.
Its main cells are:
a) parathyroid chief cell
b) oxyphil cell
These cells are spread through out the parathyroid gland. They are packed closely to the capillaries, which differentiates this gland from the thyroid gland.
The major role of parathyroid gland is to secrete parathyroid hormone. This hormone is the major regulator of calcium, phosphate and magnesium in the blood.
It increases the blood’s calcium and phosphate by bone resorption. As the values of calcium and magnesium increase, the PTH acts in the kidney by excreting the excess amount of Ca2+, and Mg2+ in the urine.
This process also applies to the values of HPO42-, it also decreases its concentration in the blood through excretion in the urine.
Another role of PTH is to secrete calcitriol, which is the active form of Vit. D. It is also known as 1, 25-dihydroxy vitamin D.
The role of calcitriol is to increase the absorption of calcium, magnesium and phosphate in the gastrointestinal tract.Reference:
Principles of Human Anatomy And Physiology by Tortora & DericksonPhoto of ">parathyroid gland