A regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action.

A synthetic substance with a similar effect to that of an animal or plant hormone.

i. Thyroxine is the main hormone secreted into the bloodstream by thethyroid gland. It plays vital roles in digestion, heart and muscle function, brain development and maintenance of bones.

ii. Oxytocin is a peptide hormone and neuropeptide. Oxytocin is normally produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, sexual reproduction, childbirth, and the period after childbirth

iii. Testosterone is the primary male sex hormone and an anabolic steroid. In male humans, testosterone plays a key role in the development of male reproductive tissues such as testes andprostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and thegrowthofbodyhair.

iv. The hormone acts mainly in the functional unit of the kidneys to aid in the conservation of sodium, secretion of potassium, water retention and to stabilize blood pressure.