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Anatomy and physiology of the neuroendocrine system
The neuroendocrine system is made up of a network of cells that are distributed throughout the body. The word neuroendocrine refers to 2 qualities of these cells: they have a similar structure to nerve cells (neurons) and produce hormones like endocrine cells. Neuroendocrine cells release hormoneshormonesA substance that regulates specific body functions, such as metabolism, growth and reproduction. into the bloodstream in response to chemical signals from other cells or messages from the nervous system. These hormones work like neurotransmitters. Neurotransmitters are chemicals released by a nerve cell to transmit signals or impulses from one nerve cell to another nerve cell or other specialized cells.
The neuroendocrine system is formed by the diffuse neuroendocrineneuroendocrineReferring to or having to do with the neuroendocrine system or the cells and organs that make up this system. system and the endocrineendocrineThe group of glands and cells in the body that make and release hormones (which control many functions such as growth, reproduction, sleep, hunger and metabolism) into the blood. system. It is made up of cells that produce and release hormones.
Diffuse neuroendocrine system
The diffuse neuroendocrine system is made up of neuroendocrine cells scattered throughout the body.
- Neuroendocrine cells in the digestive system regulate intestinal movements and the release of digestive enzymes.
- Neuroendocrine cells in the respiratory system are believed to play a role in the developmental stages of the respiratory organs. They also regulate respiratory function.
- There are small neuroendocrine organs, known as paraganglia, along the spinal column. They include the adrenal medulla inside the adrenal gland and paraganglia outside the adrenal gland. They produce the hormones epinephrine and norepinephrine. These hormones control blood pressure and heart rate.
- Neuroendocrine cells are also found in non-neuroendocrine glands and are scattered in the skin, thymus, prostate and other tissues.
The endocrine system is formed by the endocrine glands, which are ductless glands that secrete hormones directly into the blood or lymph fluid. The actions of these hormones vary according to the gland and specific type of hormone produced.
The endocrine system is made up of pituitary, pineal, thyroid, parathyroid and adrenal glands, pancreatic islet cells (also known as islets of Langerhans) and the ovaries or testicles.
- The pituitary, pineal and parathyroid glands are neuroendocrine glands.
- The thyroid gland is not a neuroendocrine gland, but it contains scattered neuroendocrine cells known as C cells.
- The adrenal glands are made up of a non-neuroendocrine area called the cortex, and a central neuroendocrine gland called the medulla.
- The pancreas is an exocrine gland, but contains scattered groups of neuroendocrine cells called pancreatic islets.
- The ovaries and testicles are not neuroendocrine glands, but contain scattered neuroendocrine cells.
Neuroendocrine cells are highly specialized nerve-like cells that release hormones in response to a neurological or chemical signal. The hormones released by the cells enter the blood and travel throughout the body to reach their target cells. Each type of hormone binds to a specific receptor on the target cell. The target cell responds to this hormone by changing specific cellular functions, such as metabolism, growth and reproduction. Complex feedback mechanisms involving the nervous system, endocrine system and diffuse neuroendocrine system control the levels of hormones in the body.
Examples of hormones and their action include:
- Insulin is produced by the pancreatic islet cells. It reduces the sugar levels in the body when they are too high. (Hypoglycemia is too little sugar in the bloodstream. Hyperglycemia is too much sugar in the bloodstream.)
- Serotonin is released by the neuroendocrine cells of the gastrointestinal tract. It regulates intestinal movement.
- Growth hormone is produced in the pituitary gland. It stimulates growth of bone and tissue.