The endocrine system

Endocrine glands

Produce and secrete hormones (chemical substances that regulate the activity of cells or organs in the body). The four major glands produces different hormones which regulate the activity of organs and tissues in the body.

Pituitary gland

Produces hormones that influence the release of hormones from other glands and regulate body functions. It is controlled by the hypothalamus which receives information from many sources about the basic functions of the body, then uses this information to help regulate these functions. It produces hormones that travel in the bloodstream to their specific target and can directly cause changes in physiological processes in the body. Or it stimulates other glands to produce other hormones.

Hormones produced by the adrenal glands (adrenal cortex)

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 inability to deal with stress. The adrenal cortex also produces aldosterone which is responsible for maintaining blood volume and blood pressure.

Hormones produced by the adrenal glands (adrenal medulla)

The adrenal medulla releases adrenaline and noradrenaline which are hormones that prepare the body for fight or flight. Adrenaline helps the body respond to a stressful situation, for example, increasing heart 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.

Hormones produced by the pituitary gland (anterior)

The anterior pituitary gland releases ACTH as a response to stress. ACTH stimulates the adrenal glands to produce cortisol . It also produces LH and FSH which in females stimulates the ovaries to produce oestrogen and in males stimulate the testes to produce testosterone and sperm.

Pituitary glands (anterior and posterior)

The pituitary gland has two main parts; anterior (front) and posterior (back). These two parts release different hormones which target different parts of the body. The two sections of the pituitary gland produce a number of different hormones, which act of different target glands or cells.

Hormones produced by the pituitary gland (posterior)

The posterior pituitary gland releases oxytocin which stimulates contraction of the uterus during childbirth, and is important for mother-infant bonding.

Adrenal glands

The two adrenal glands sit on top of the kidneys and is made up of two parts. The outer part if each gland is the adrenal cortex and the inner part is the adrenal medulla. The two parts are very different but one of the main distinctions is that the hormones released by the adrenal cortex are necessary for life and those released buy the adrenal medulla are not.

Timing and levels of hormone release

Timing is critical for normal functioning, as are the levels of hormones released. Too much or too little at the wrong time can result in dysfunction of bodily systems.

The 4 main endocrine glands

1) Pituitary gland - known as the 'master gland' which regulates the ES 2) Adrenal gland - facilitates the release of adrenaline as part of the fight-or-flight response 3) Testes - facilitate the release of testosterone (male hormone) 4) Ovaries - facilitates the release of oestrogen and progesterone (female hormones)

Endocrine system regulation

A signal is sent from the hypothalamus to the pituitary gland in the form of a 'releasing hormone'. This causes the pituitary to secrete a 'stimulating hormone' into the bloodstream which signals the target gland to secrete its hormone. As levels of this hormone rises in the bloodstream, the hypothalamus shuts down secretion of the releasing hormone and the pituitary gland shuts down secretion of the stimulating hormone, resulting in stable concentrations of hormones circulating in the bloodstream.

Hormones

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, it only affects a limited number of cells, known as target cells. Target cells respond to a particular hormone because they have receptors for that hormone. When enough receptor sites are stimulated by hormones, this results in a physiological reaction in the target cell.

Negative feedback

High levels of hormones produced in other endocrine glands can stop the hypothalamus and pituitary releasing more of their own hormones. This is called negative feedback and prevents hormone levels from rising too high.

Endocrine system

A network of glands throughout the body that manufacture and secrete chemical messengers known as hormones. It works alongside the nervous system to regulate vital physiological processes of the human body. Instead of using nerves to transmit information, it uses blood vessels to deliver hormones to their target sites in the body.