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.

Where neuroendocrine cells are located

Neuroendocrine cells are found in almost every organ of the body. They are mainly found scattered in the gastrointestinal (GI) tract (including the small intestine, rectum, stomach, colon, esophagus and appendix), the gallbladder, the pancreas (islet cells) and the thyroid (C cells). Neuroendocrine cells are also commonly found in the lungs or airways into the lungs (bronchi), as well as the respiratory tract of the head and neck. The neuroendocrine cells scattered throughout these organs are often referred to as the diffuse neuroendocrine system.

The pituitary gland, the parathyroid glands and the inner layer of the adrenal gland (adrenal medulla) are almost all made up of neuroendocrine cells.

Other sites of neuroendocrine cells include the thymus, kidneys, liver, prostate, skin, cervix, ovaries and testicles.

Diagram of part of the neuroendocrine system
Diagram of part of the neuroendocrine system

What neuroendocrine cells do

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.

Expert review and references

  • American Cancer Society . Gastrointestinal Carcinoid Tumors . 2015 :
  • American Society of Clinical Oncology. Neuroendocrine Tumor. 2014:
  • Carcinoid Neuroendocrine Tumour Society (CNETS) Canada . Neuroendocrine Tumours: Reference Guide for Patients and Families . 2013 :
  • Gomez-Hernandez K, Ezzat S . Clinical presentations of endocrine diseases. Mete O, Asa SL (eds.). Endocrine Pathology. United Kingdom: Cambridge University Press; 2016: 1:1-55.
  • Inzani F, Rindi G . Neuroendocrine neoplasms of the pancreas. Mete O, Asa SL (eds.). Endocrine Pathology. United Kingdom: Cambridge University Press; 2016: 18D:726-742.
  • Macmillan Cancer Support. Neuroendocrine Tumours (NETs). 2013:
  • Martini FH, Timmons MJ, Tallitsch RB. Human Anatomy. 7th ed. San Francisco: Pearson Benjamin Cummings; 2012.
  • Penn Medicine. All About Carcinoid and Neuroendocrine Tumors. University of Pennsylvania; 2011:
  • Serra S . Endocrine lesions of the gastrointestinal tract. Mete O, Asa SL (eds.). Endocrine Pathology. United Kingdom: Cambridge University Press; 2016: 17:677-717.
  • Young B, O'Dowd G, Woodford P (eds.). Wheaters's Functional Histology. 6th ed. Churchill Livingston; 2014.

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