6.2.1 The Function of the Endocrine System

• The human endocrine system is composed of glands that secrete chemicals called hormones directly into the bloodstream
• The blood carries the hormone around the body, and when it reaches a target cell/organ it produces an effect
• Compared to the nervous system the effects of hormones are slower but they act for longer
• Important structures in the endocrine system are:
  • Pituitary gland: the ‘master gland’ making hormones e.g. Follicle Stimulating Hormone
  • The pancreas: produces insulin which regulates the blood glucose level
  • The thyroid: produces thyroxine which controls the metabolic rate and affects growth
  • Adrenal glands: produces adrenaline
  • Ovaries (females): produce estrogen
  • Testes (males): produce testosterone

The major endocrine glands in the body secrete hormones which circulate around the body in the bloodstream

• The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions
• These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects
  • For example, in certain conditions, the pituitary gland makes and secretes thyroid-stimulating hormone (TSH) which stimulates the thyroid to release thyroxine

Hormones are synthesized and released into the bloodstream from a gland (such as the pituitary gland) and circulate in the bloodstream, having an effect on target cells