Write short notes on the functions of the following hormones :

(a) Parathyroid hormone (PTH)

(b) Thyroid hormone

(c) Thymosins

(d) Androgens

(e) Estrogens

(f) Insulin and glucogon

(a) Parathyroid hormone 

The principal/chief cells of the parathyroid produce the parathyroid hormone, also called the parathormone. The function of this hormone is 

• To maintain calcium and phosphate balance in the blood and other tissues.
• To increase calcium reabsorption from the intestine as well as from the nephrons of the kidney
• To initiate bone resorption (e.g. reabsorption of calcium from bones), in case the blood calcium levels drop.

(b) Thyroid hormone

Both the thyroid hormones T${}_4$ (Thyroxine) and T${}_3$ (active form) are secreted by the thyroid gland.

• The thyroid hormones control the metabolism of carbohydrates, protein and fats. They play an important role in regulating the Basal Metabolic Rate (BMR)
  
• They are also important for maintenance of water and electrolyte balance. 
  
• Thyroid hormones also regulate the RBC production.
  
• The thyrocalcitonin maintains the blood calcium levels and promotes the bone formation.
  

(C) Thymosins

The thymus actively secretes the hormones called thymosins (only till pre-pubescence)

• The stimulation, development and differntiation of T-lymphocytes.
• The development of cell-mediated immunity (T-lymphocytes mediated immunity)
• The production of antibodies (Humoral immunity).

(d) Androgens

• Androgens are the hormones which are responsible for the development of secondary sexual characters. The Leydig cells of testis produce androgens such as testosterone. 
  
• Androgens are also produced by the adrenal cortex of the adrenal gland and the ovaries 

(e) Estrogens

• In Non-pregnant females, they are predominantly secreted by the ovaries. However, during pregnancy, the placenta secretes a lot of estrogens.
• The three types of estrogens are; $\beta$-estradiol, estrone and estriol.
• The most active and the principal estrogen produced by the ovaries is the  $\beta$-estradiol. 
• They play an important role in the growth and development of ovarian follicles and breast
• They are responsible for the development of secondary sexual characteristics (e.g. high pitch voice)
• They inhibit osteoclastic activity and stimulate bone growth. Osteoporosis in menopausal women is because of reduced estrogen levels.

They also influence the texture of the skin and female sexual behaviour

(f) Insulin and Glucagon

Glucagon

• It increases the blood glucose levels by initiating glycogenolysis (glycogen degradation) and stimulating gluconeogenesis (synthesis of glucose from non-carbohydrate molecules) in the liver cells.
• Since it increases the blood glucose levels it is a hyperglycemic (hyper-more, glycemic-sugar levels) hormone
• It also initiates lipolysis (degradation of lipid) in the adipose tissue.

Insulin

• It is released when the glucose level in the blood raises.
• It lowers blood sugar levels in different ways; increasing the uptake of glucose by all the cells in the body, initiating glycogenesis (glycogen synthesis) in the liver and muscle.
• It initiates lipogenesis (synthesis of lipids/fat) and storage of fat in adipose tissue and inhibits gluconeogenesis
• It is a hypoglycemic (hypo=less) hormone as it reduces the sugar levels in the blood