How does the pituitary gland work?
The pituitary gland (hypophysis) controls important body functions and the hormonal system. It is a protrusion at the base of the brain and about the size of a pea or cherry, which is why it is called “hypophysis” (Greek for “growth attached below”). The gland lies well protected in a small cavity of the cranial bones, level with the nose, and in the middle of the head.
The pituitary gland and the hypothalamus – a part of the interbrain – both control the involuntary nervous system, which manages the balance of energy, heat and water in the body. Body temperature, heart beat or the amount of urine are all regulated this way, for example, and so are sleep, hunger and thirst. The pituitary gland also produces a series of hormones that either control most of the other hormone glands in the body or have a direct effect on specific organs.
The pituitary gland is made up of four parts:
- Anterior lobe of pituitary (anterior pituitary)
- Posterior lobe of pituitary (posterior pituitary)
- The intermediate part between both lobes (pars intermedia)
- Pituitary stalk, which forms the connection to the interbrain
The anterior and the posterior lobe function independently of each other. Whereas the posterior lobe is directly connected to the interbrain (hypothalamus), there is no such connection from the anterior pituitary, where hormones are produced.
The anterior lobe makes up about three quarters of the overall mass of the hypophysis and consists of gland tissue. Two kinds of hormones are made here:
- Hormones that control other hormone glands
- Hormones that have a direct effect on the body
The group of glands that control hormones includes:
- Thyroid-stimulating hormone (TSH), which regulates hormone production in the thyroid gland,
- Adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to produce hormones,
- Follicle-stimulating hormone (FSH), which regulates hormone production in the ovaries and testicles,
- Luteinizing hormone (LH), which also has an effect on hormone production in the ovaries and testicles.
The group of hormones that have a direct effect includes:
- Growth hormone (GH), also called somatotropic hormone (STH), which has an effect particularly on the liver and the bones, and on fat, muscle and many other tissues and organs in the body
- Prolactin, which influences the mammary glands and ovaries.
The hormones are released by the pituitary gland into the bloodstream and then reach the various organs they have an effect on. TSH, for example, stimulates the thyroid gland to produce more or less thyroid hormones, depending on how much is needed. Prolactin stimulates breast growth in puberty, sets off milk production in the breasts and suppresses ovulation.
There are two mechanisms that regulate hormone production in the anterior lobe itself:
- Releasing or inhibiting hormones produced by the hypothalamus.
- Hormone level in the blood: When the level of thyroid hormones in the body is high enough, for example, the pituitary gland stops producing the hormone that stimulates the thyroid gland. This works the other way round, too: When the hormone level is too low, hypophysis and hypothalamus increase the production of thyroid-stimulating hormone. The thyroid gland will then produce more thyroid hormones.
You can read more about how the thyroid gland works here.
The posterior lobe mainly consists of entangled nerve fibers coming from the hypothalamus. The posterior lobe stores two different hormones, which are released if needed:
- Oxytocin has an effect on the womb and the mammary glands,
- Vasopressin, also called antidiuretic hormone (ADH), influences the kidney and blood vessels.
In pregnant women, oxytocin causes contractions during labor, for example. Vasopressin plays an important role in the regulation of the amount of water in the body.
Intermediate part (Pars intermedia)
In the intermediate part between the anterior and the posterior pituitary, there is also tissue that produces a hormone:
- Melanocyte-stimulating hormone (MSH) or intermedin, which mainly affects the skin, but also the nerve cells in the brain.
MSH stimulates melanin production in the skin, a pigment that protects against the harmful ultraviolet rays of the sun. MSH also regulates our appetite and influences sexual drive.
The pituitary stalk connects the posterior lobe directly to the interbrain, or more precisely, to the hypothalamus.
Author: German Institute for Quality and Efficiency in Health Care (IQWiG)