The endocrine system uses hormones to send information about changes in the environment around the body to bring about a designated response.

The endocrine system consists of all the endocrine glands in the body.

Endocrine glands are groups of cells that secrete hormones directly into the bloodstream.

Some examples include the pancreas, pituitary gland, and adrenal glands.

Target cells are cells that have specific receptors for a hormone. Once the hormone binds to the receptors, it stimulates the target cells to produce a response.

1. Hormones are chemical messengers that are produced in endocrine gland cells.
2. They are secreted directly into the blood when the gland is stimulated.
3. The blood transports hormones to their target cells.
4. Hormones bind to receptors on or in target cells.
5. Target cells are stimulated to produce a response.

1. Water soluble (hydrophilic)
2. Cannot diffuse across the phospholipid bilayer
3. Bind to receptors on the cell-surface membrane of their target cells to activate second messengers

The pituitary gland produces several different hormones, many of which in turn control the release of other hormones.

The pituitary gland is located at the base of the brain.

1. Communication: the nervous system uses action potentials transmitted along neurones, while the endocrine system uses hormones transmitted in the blood
2. Transmission speed: the nervous system is faster than the endocrine system
3. Duration of effect: effects of the nervous system have a shorter duration
4. Area of response: nervous system responses are localised, while endocrine system responses can be widespread

1. Lipid soluble (hydrophobic)
2. Can diffuse across the phospholipid bilayer
3. Bind to receptor molecules in the cytoplasm or the nucleus

When steroid hormones bind to steroid hormone receptors they form a hormone-receptor complex that can act as a transcription factor.