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Overview of the Pituitary Gland

By

John D. Carmichael

, MD, Keck School of Medicine of the University of Southern California

Last full review/revision Mar 2021| Content last modified Mar 2021
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The pituitary is a pea-sized gland that is housed within a bony structure (sella turcica) at the base of the brain. The sella turcica protects the pituitary but allows very little room for expansion.

The pituitary controls the function of most other endocrine glands and is therefore sometimes called the master gland. In turn, the pituitary is controlled in large part by the hypothalamus, a region of the brain that lies just above the pituitary. By detecting the levels of hormones produced by glands under the pituitary's control (target glands), the hypothalamus or the pituitary can determine how much stimulation the target glands need.

The Pituitary and Its Target Organs

The pituitary has two distinct parts:

  • Front (anterior) lobe, which accounts for 80% of the pituitary gland's weight

  • Back (posterior) lobe

The lobes are connected to the hypothalamus by a stalk that contains blood vessels and nerve cell projections (nerve fibers, or axons). The hypothalamus controls the anterior lobe by releasing hormones through the connecting blood vessels. It controls the posterior lobe through nerve impulses.

The hormones produced by the pituitary are not all produced continuously. Most are released in bursts every 1 to 3 hours, with alternating periods of activity and inactivity. Some of the hormones, such as adrenocorticotropic hormone (ACTH), growth hormone, and prolactin, follow a circadian rhythm: The levels rise and fall predictably during the day, usually peaking just before awakening and dropping to their lowest levels just before sleep. The levels of other hormones vary according to other factors. For example, in women, the levels of luteinizing hormone and follicle-stimulating hormone, which control reproductive functions, vary during the menstrual cycle.

Pituitary: The Master Gland

The pituitary, a pea-sized gland at the base of the brain, produces a number of hormones. Each of these hormones affects a specific part of the body (a target organ or tissue). Because the pituitary controls the function of most other endocrine glands, it is often called the master gland.

Hormone

Target Organ or Tissue

Adrenocorticotropic hormone(ACTH)

Adrenal glands

Beta-melanocyte–stimulating hormone

Skin

Endorphins

Brain and immune system

Enkephalins

Brain

Follicle-stimulating hormone

Ovaries or testes

Growth hormone

Muscles and bones

Luteinizing hormone

Ovaries or testes

Oxytocin*

Uterus and mammary glands

Prolactin

Mammary glands

Thyroid-stimulating hormone

Thyroid gland

Vasopressin (antidiuretic hormone)*

Kidneys

Locating the Pituitary Gland

* These hormones are produced in the hypothalamus but are stored in and released from the pituitary.

Anterior lobe hormones

The anterior lobe of the pituitary produces and releases (secretes) six main hormones:

  • Adrenocorticotropic hormone (ACTH), also called corticotropin, which stimulates the adrenal glands to produce cortisol and other hormones

  • Follicle-stimulating hormone and luteinizing hormone (the gonadotropins), which stimulate the testes to produce sperm, the ovaries to produce eggs, and the sex organs to produce sex hormones (testosterone and estrogen)

  • Growth hormone, which regulates growth and physical development and has important effects on body shape by stimulating muscle formation and reducing fat tissue

  • Prolactin, which stimulates the mammary glands of the breasts to produce milk

  • Thyroid-stimulating hormone, which stimulates the thyroid gland to produce thyroid hormones

The anterior lobe also produces several other hormones, including one that causes the skin to darken (beta-melanocyte–stimulating hormone) and ones that inhibit pain sensations (enkephalins and endorphins) and help control the immune system (endorphins).

Posterior lobe hormones

The posterior lobe of the pituitary produces only two hormones:

  • Vasopressin

  • Oxytocin

Oxytocin causes the uterus to contract during childbirth and immediately after delivery to prevent excessive bleeding. Oxytocin also stimulates contractions of the milk ducts in the breast, which move milk to the nipple (the let-down) in lactating women. Oxytocin has some additional roles in both men and women.

Pituitary gland malfunction

The pituitary gland can malfunction in several ways, usually as a result of developing a noncancerous tumor (adenoma). The tumor may overproduce one or more pituitary hormones, or the tumor may press on the normal pituitary cells, causing underproduction of one or more pituitary hormones.

The tumor may also cause enlargement of the pituitary gland Enlargement of the Pituitary Gland Enlargement of the pituitary gland is usually due to a tumor but may be due to bleeding into the gland or involvement by some other disease, such as tuberculosis or sarcoidosis. In some cases... read more , with or without disturbing hormone production. Sometimes there is overproduction of one hormone by a pituitary tumor and underproduction of another at the same time due to pressure.

Sometimes excess cerebrospinal fluid can fill the space around the pituitary gland and compress it (resulting in empty sella syndrome Empty Sella Syndrome In empty sella syndrome, the sella turcica (the bony structure at the base of the brain that houses the pituitary gland) fills with cerebrospinal fluid, partially or completely compressing the... read more ). The pressure may cause the pituitary to overproduce or underproduce hormones.

Too little or too much of a pituitary hormone results in a wide variety of symptoms.

Overproduction of pituitary hormones causes disorders, including

Underproduction of pituitary hormones causes disorders, including

Doctors can diagnose pituitary gland malfunction using several tests. Imaging tests, such as a computed tomography (CT) or magnetic resonance imaging (MRI), can show whether the pituitary has enlarged (for example, if a pituitary tumor Enlargement of the Pituitary Gland Enlargement of the pituitary gland is usually due to a tumor but may be due to bleeding into the gland or involvement by some other disease, such as tuberculosis or sarcoidosis. In some cases... read more is present) or shrunk (for example, in hypopituitarism Hypopituitarism Hypopituitarism is an underactive pituitary gland that results in deficiency of one or more pituitary hormones. Symptoms of hypopituitarism depend on what hormone is deficient and may include... read more ). Such tests can usually determine whether a tumor exists in the gland.

Doctors can measure the levels of pituitary hormones, usually by a simple blood test. Doctors select which pituitary hormone levels they want to measure depending on the person's symptoms. Sometimes, levels of pituitary hormones are not easy to interpret because the levels vary greatly during the day and according to the body's needs. For these hormones, measuring a random blood sample does not provide useful information.

For some of those hormones, doctors give a substance that would normally affect hormone production and then they measure the level of the hormone. For example, if a doctor injects insulin, the levels of ACTH, growth hormone, and prolactin should increase. Rather than measuring growth hormone levels directly, doctors often measure another hormone, insulin-like growth factor 1 (IGF-1). Growth hormone is produced in bursts and its levels quickly fall, but IGF-1 levels reflect the overall daily production of growth hormone. For all of these reasons, interpreting the results of blood tests for pituitary hormones is complex.

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Endocrine Glands
The endocrine system is made up of glands and organs that regulate and control many bodily functions by producing and secreting hormones, chemicals that affect various bodily activities. Which of the following is known as the master gland because it helps regulate the function of many of the body’s endocrine glands?
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