Endocrinology 101

What is the Endocrine System?

The endocrine system is a complex collection of hormone-producing glands that control basic body functions such as metabolism, growth and sexual development. The amount of hormones produced by each gland is carefully balanced. Too much or too little of a certain hormone can have effects throughout the body and cause various endocrine disorders.

Many of the hormones produced by the endocrine glands interact with each other to maintain balance. The endocrine system consists of:

pituitary gland - secretes hormones to stimulate the adrenals, thyroid, pigment-producing skin cells and gonads (ovaries and testes). Also secretes a growth hormone, an antidiuretic hormone, prolactin (a hormone which affects milk production after childbirth), and oxytocin (a hormone which plays a role in childbirth).
hypothalamus - secretes hormones that stimulate or suppress the release of hormones in the pituitary gland.
pancreas - secretes insulin and glucagon, which affect the body's absorption of glucose, the body's main source of energy.
adrenal cortex - secretes hydrocortisone, which affects metabolism. Also secretes androgen hormone and aldosterone, which affect blood pressure and saline balance.
thyroid gland - secretes thyroxin, triiodothyronine and calcitonin, which affect metabolism, body heat, and bone growth.
parathyroid glands - secretes a parathyroid hormone, which affects calcium levels in the blood.
gonads - the male and female reproductive glands (testes and ovaries). The testes secrete testosterone, which stimulate sperm production and other male characteristics. The ovaries secrete estrogen and progesterone, which affect many aspects of the female body, including menstrual cycles and pregnancy.

The exocrine glands actually secrete their substances through ducts to particular areas. Examples of exocrine glands include the salivary glands and the sweat glands. The endocrine glands, on the other hand, secrete the hormones they produce directly into the bloodstream. Most endocrine glands are controlled by trophic (stimulating) hormones secreted by the pituitary gland. The pituitary gland, in turn, is controlled by hormones secreted by the hypothalamus in the brain.