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 and similar substances (peptides) 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, which include controlling:

• 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 or peptides released by neuroendocrine cells and what they do.

• Serotonin (5-HT or 5-hydroxytryptamine) is a chemical released by nerve cells (neurotransmitter) that helps with digestion. A lot of the body’s serotonin is found and made in the neuroendocrine cells of the GI tract where it controls the movement of food through the GI tract.
• Gastrin 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.
• Epinephrine (adrenaline) is made by neuroendocrine cells of the adrenal gland. It is released during times of stress, like when you feel fear, and increases heart rate and blood pressure.
• Growth hormone is made in the pituitary gland. It promotes the growth and development of bones and muscles.