Parathyroid gland
There are four small parathyroid gland.
Two embedded in posterior surface of each lateral lobe of thyroid gland.
They are surrounded by fine connective tissue capsule.
They are small light colored clumps that stick out surface of thyroid gland.
Size; 4 glands, each about 3-8mm long and 2-5mm wide.
Each mass is about 40mg.
Parathyroid gland composed of two major cells;
1. Chief cells (produce parathyroid hormone)
2. Oxyphils cells
Parathyroid hormone (PTH) or Parathormone
Parathyroid gland secrete parathyroid hormone (PTH).
Secretion is regulated by blood calcium level.
When they fall, secretion of PTH is increases and vice-versa.
Function
The main function of PTH is to increase blood calcium level when it is low.
PTH is major regulator of level of calcium, magnesium and phosphate ions in blood.
This is achieved by indirectly increasing amount of calcium absorbed from small intestinal mucosal cells.
Enhancing reabsorption of calcium by renal tubule.
If these sources provide inadequate supplies then PTH stimulates osteoclasts (bone destroying cells) and calcium is released from bones into blood.
Para hormone and calcitonin from thyroid gland act in complementary manner to maintain blood calcium levels within normal range. This is needed for;
Muscle contraction, nerve transmission, blood clotting, normal action of many enzyme.
Vitamin D is required for absorption of calcium from digested food.
Regulation of Secretion
Production of hormone directly controlled by calcium concentration of blood.
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