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The median eminence is a brain structure that secretes substances controlling the pituitary gland and regulates reproduction, growth, stress, and metabolism. It has four zones and nerve cells that release dopamine, GHRH, somatostatin, and CRH. Damage can affect hormone production and cause symptoms.
Located at the base of a brain structure called the hypothalamus, the median eminence normally secretes substances that control the pituitary gland, which releases many of the body’s hormones. The median eminence is typically found behind the location where the optic nerves cross and is also near the neural connection between the hypothalamus and the pituitary gland. Nerve extensions called axons extend into the structure from other parts of the brain. The external part generally has a network of nerve endings and small portal blood vessels that carry substances to the pituitary gland.
Neurons that release substances such as dopamine, growth hormone-releasing hormone (GHRH), somatostatin, and corticotropin-releasing hormone (CRH) usually terminate in the median eminence. The compounds released by these cells can enter the blood when needed. The internal portal system typically comprises three cellular layers that control secretion based on signals sent and received. Nerve endings and neurological components called glial cells are found in the region, although synapses, or the communicating ends of nerve cells, are not typically found here.
The median eminence typically acts as a link between neurological hormonal control and the endocrine system. Reproduction, growth, stress and metabolism can all be regulated by activity in this part of the brain. The blood barrier in the structure is usually porous, so it can respond to chemical signals in the circulatory system as well as other parts of the brain called the circumventricular organs. It is also part of the pituitary portal system, where nerve signals are typically sent to the body’s endocrine glands.
Under the microscope, the median eminence usually has four different zones, which are differentiated by the types of cells located in each. Areas include ventricular, myelinated axon, neural outline, and capillary zones. Nerve cell terminals in the capillary area are normally connected to openings in small blood vessels where secretions can pass into the blood.
The overall function of the median eminence can change with age. Also capable of secreting gonadotropin-releasing hormone (GnRH), the region can slow down the release of this substance; typically does so when a mammal is not reproducing; the pattern in which this occurs often depends on age and species. Damage to the median eminence, which can disrupt communication between different cells, sometimes affects the function of the pituitary gland. The abnormal hormone production can then cause various symptoms, including extreme thirst or frequent urination.
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