The neuroendocrine system

The neuroendocrine system is made up of special cells called neuroendocrine cells. They are spread throughout the body. Neuroendocrine cells are like nerve cells (neurons), but they also make hormones like cells of the endocrine system (endocrine cells). They receive messages (signals) from the nervous system and respond by making and releasing hormones. These hormones control many body functions.

Neuroendocrine cells make and release hormones in response to neurological or chemical signals. The hormones then enter the blood and travel throughout the body to other cells (target cells). The hormones attach to specific receptors on target cells, which cause changes in the cells and what they do.

Neuroendocrine cells have many functions. These cells control:

• the release of digestive enzymes to break down food
• how fast food moves through the GI tract
• air and blood flow through the lungs
• blood pressure and heart rate
• the amount of sugar (glucose) in the blood
• bone and muscle growth and development

The following are examples of hormones that neuroendocrine cells release.

Serotonin (5-HT or 5-hydroxytryptamine) is mostly made by neuroendocrine cells of the GI tract. It helps control the movement of food as you digest it. A smaller amount of serotonin is made in the brain by nerve cells and helps with other body functions.

Somatostatin is made by many organs, including the GI tract, pancreas and hypothalamus. It prevents the body from releasing growth hormone, thyroid-stimulating hormone and other hormones to control body functions.

Gastrin is made by neuroendocrine cells of the stomach. It tells the stomach to release acid and enzymes to help with digestion.

Insulin is made by pancreatic islet cells. It lowers the level of sugar (glucose) in the blood when it’s high. It controls when cells absorb (take up) sugar for energy.

Glucagon is also made by pancreatic islet cells. It increases the level of glucose in the blood when it’s low. It controls when the liver and other body tissues release stored sugar into the blood.

Cholecystokinin is made by neuroendocrine cells in the duodenum. It tells the gallbladder to release bile and the pancreas to release digestive enzymes to help with digestion.

Epinephrine (adrenaline) is made by neuroendocrine cells of the adrenal gland. It is released when you are stressed or feel fear and increases heart rate and blood pressure.

Growth hormone is made by neuroendocrine cells of the pituitary gland. It promotes the growth and development of bones and muscles.

Adrenocorticotrophic hormone (ACTH) is also made in the pituitary gland. It tells the adrenal glands to make cortisol and other steroid hormones.

Other hormones made by neuroendocrine cells of the pituitary gland include follicle-stimulating hormone (FSH), luteinizing hormone (LH) and thyroid-stimulating hormone (TSH).