(a) Parathyroid hormone $(\mathbf{P T H})$
- When the level of calcium ions in the plasma decreases, PTH is secreted.
- It increases the level of $\mathrm{Ca}^{2+}$ ions in the blood/ plasma by
(i) bone reabsorption (demineralisation/ dissolution of bones).
(ii) stimulating reabsorption of $\mathrm{Ca}^{2+}$ ions by the renal tubules.
(iii) stimulating the absorption of $\mathrm{Ca}^{2+}$ from the alimentary canal.
(iv) since it increases the level of $\mathrm{Ca}^{2+}$ ions in the blood, it is called hypercalcemic hormone.
- Along with TCT, PTH plays an important role in the calcium balance of the body.
(b) Thyroid hormones: Two types of thyroid hormones -
(i) Tetraiodothyronine $\left(\mathrm{T}_4\right)$
(ii) Triiodothyronine( $\left.\mathrm{T}_3\right)$
Thyroid hormones perform the following functions :
(i) They regulate the basal metabolic rate.
(ii) They control the metabolism of carbohydrates, fats and protein.
(iii) They influence the maintenance of water and electrolyte balance.
(iv) They support the process of red blood cells formation.
(c) Thymosin : Thymosin is secreted by thymus and plays a major role in the differentiation of Tlymphocytes, which provided cell mediated immunity. Thymosins also promote production of antibodies to provide humoral immunity.
(d) Androgens : Androgens are secreted from the leydig cells of testis.
Functions:
(i) Androgens regulate the development, maturation and functioning of the male secondary sex organs.
(ii) They stimulate spermatogenesis.
(iii) They act on the CNS and the influence on male sexual behaviour.
(iv) They produce anabolic effects on proteinsand carbohydrate metabolism.
(e) Estrogens: Ovarian hormone.
Functions: Stimulates the growth and functioning of female sex organs.
- It stimulates the development of female sexcharacteristics.
- It regulates the female sexual behaviour.
(f) Insulin and Glucagon: Secreted by pancreas.
- Insulin is a peptide hormone which plays a major role in the regulation of glucose homeostasis. Insulin mainly acts on hepatocytes and adipocytes (cells of adipose tissue) and enhancing cellular glucose uptake and utilisation.
- Glucagon is also a peptide hormone and plays
an important role in maintaining the normal blood glucose levels.
- Glucagon acts mainly on the liver cells (hepatocytes) and stimulates glycogenolysis resulting in an increased blood sugar (hyperglycemia).
- This hormone also stimulates the process of gluconeogenesis which also contributes to hyperglycemia.
- Glucagon reduces the cellular glucose uptake and utilisation. Thus glucagon is a hyperglycemic hormone.