Hormones are signal molecules that the body uses to regulate the physiological functions of organs, tissues, and cells. They follow the lock-and-key mechanism in their mode of action because they target specific receptions in cells, tissues, and organs within the body. The major endocrine glands are the pineal gland, pituitary glands (anterior and posterior), thyroid gland, adrenal gland (medulla and cortex), ovary, testes, pancreas, kidney, and hypothalamus. The pineal gland releases melatonin and regulates circadian rhythm in the body, while pituitary glands secrete growth hormone, prolactin, oxytocin, and follicle-stimulating hormone.
Adrenal glands secrete hormones such as glucocorticoids and epinephrine hormones involved in regulating metabolic activities in the body. Ovary and testes release estrogens and androgens, respectively, which are sex hormones functioning to regulate reproduction processes. The pancreas produces insulin and glucagon thatregulate glucose levels in the body, whereas the kidney releases the renin hormone involved in controlling osmotic pressure in the blood.