The human endocrine system

• The endocrine system is composed of glands that secrete hormones directly into the bloodstream.
• Hormones are large molecules. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer
• The pituitary gland in the brain is a ‘master gland’. It secretes several hormones that act on other glands to stimulate other hormones to be released.
• Adrenaline is produced by the adrenal gland. It boosts the delivery of oxygen and glucose to the brain and muscles and prepares the body for ‘flight or fight’
• Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.
• The control of thyroxine levels involves negative feedback. Negative feedback tends to stabilise a system. Any change in the system leads to a response that tends to reverse the change