Thyroid hormones play an important role in the regulation of the basal metabolic rate. These hormones also support the process of red blood cell formation. Thyroid hormones control the metabolism of carbohydrates, proteins and fats. Maintenance of water and electrolyte balance is also influenced by thyroid hormones.
Thyroid gland also secretes a protein hormone called thyrocalcitonin (TCT) which regulates the blood calcium levels. . . Parathyroid Gland In humans, four parathyroid glands are present on the back side of the thyroid gland, one pair each in the two lobes of the thyroid gland (Figure .
b). The parathyroid glands secrete a peptide hormone called parathyroid hormone (PTH). The secretion of PTH is regulated by the circulating levels of calcium ions. Parathyroid hormone (PTH) increases the Ca + levels in the blood.
PTH acts on bones and stimulates the process of bone resorption (dissolution/ demineralisation). PTH also stimulates reabsorption of Ca + by the renal tubules and increases Ca + absorption from the digested food. It is, thus, clear that PTH is a hypercalcemic hormone, i.e., it increases the blood Ca + levels. Along with TCT, it plays a significant role in calcium balance in the body.
. . Thymus The thymus gland is a lobular structure located between lungs behind sternum on the ventral side of aorta. The thymus plays a major role in the development of the immune system.
This gland secretes the peptide hormones called thymosins . Thymosins play a major role in the differentiation of T-lymphocytes , which provide cell-mediated immunity . In addition, thymosins also promote production of antibodies to provide humoral immunity . Thymus is degenerated in old individuals resulting in a decreased production of thymosins.
As a result, the immune responses of old persons become weak. The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine . These are commonly called as catecholamines . Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones or hormones of Fight or Flight .
These hormones increase alertness, pupilary dilation, piloerection (raising