Merck Manual

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Overview of the Pituitary Gland


John D. Carmichael


Topic Resources



The Pituitary and Its Target Organs

The Pituitary and Its Target Organs

The pituitary has two distinct parts:


  • Back (posterior) lobe



Pituitary: The Master Gland



Target Organ or Tissue

Adrenocorticotropic hormone(ACTH)

Adrenal glands

Beta-melanocyte–stimulating hormone



Brain and immune system



Follicle-stimulating hormone

Ovaries or testes

Growth hormone

Muscles and bones

Luteinizing hormone

Ovaries or testes


Uterus and mammary glands


Mammary glands

Thyroid-stimulating hormone

Thyroid gland

Vasopressin (antidiuretic hormone)*


Locating the Pituitary Gland

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

Anterior lobe hormones








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 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.


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.



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