The endocrine system

• endocrine glands produce and secrete hormones, chemical substances that regulate the activity of cells or organs in the body
• the major glands of the endocrine system include the pituitary gland, adrenal glands and the reproductive organs
• each gland in the endocrine system produces different hormones, which regulate the activity of organs and tissues in the body
• hormones are chemicals that circulate in the bloodstream and are carried to target sites throughout the body
• although hormones come into contact with most cells in the body, a given hormone usually affects only a limited number of cells, known as target cells
• target cells respond to a particular hormone because they have receptors for that hormone
• cells that don't have such a receptor cannot be influenced directly by the hormone. when enough receptor sites are stimulated by hormones, this results in a physiological reaction in the target cell
• the pituitary gland produces hormones whose primary function is to influence the release of hormones from other glands, and in doing so regulate many of the body's functions
• the pituitary controlled by the hypothalamus, a region of the brain just above the pituitary gland
• the hypothalamus receives information from many sources about the basic functions of the body, and then uses this information to help regulate these functions
• the two adrenal glands sit on top of the kidneys. the name 'adrenal' relates to their location. each adrenal gland is made up of two distinct parts
• the outer part of each gland is called the adrenal cortex and the inner region is known as the adrenal medulla
• the adrenal cortex and the adrenal medulla have very different functions
• one of the main distinctions between them is that the hormones released by the adrenal cortex are necessary for life; those released by the adrenal medulla are not
• the adrenal cortex produces cortisol, which regulates or supports a variety of important bodily functions including cardiovascular and anti-inflammatory functions
• cortisol production is increased in response to stress. if the cortisol level is low, the individual has low blood pressure, poor immune function and an ability to deal with stress
• the adrenal medulla released adrenaline and noradrenaline, hormones that prepare the body for fight or flight
• adrenaline helps the body to respond to a stressful situation, for example by increasing hart rate and blood flow to the muscles and brain and helping with the conversion of glycogen to glucose to provide energy
• noradrenaline constricts the blood vessels, causing blood pressure to increase