Pituitary Gland: Definition, Function, Morphology and Associated Disorders

It is a pea-sized gland found within a bony structure, called a Turkish chair, located at the base of the brain.

Function

The Turkish chair protects the pituitary but allows very little space for its expansion.

The pituitary gland is responsible for controlling the activity of most endocrine glands, so it is also known as the master gland.

By detecting the levels of hormones produced by the glands under the control of the pituitary gland, the pituitary gland can determine how much stimulation the target glands need.

Morphology

The pituitary gland has two distinct parts:

  • Frontal or anterior lobe, which represents 80% of the weight of the pituitary gland.
  • Posterior lobe.

The lobes are connected to the hypothalamus by a stem that contains blood vessels and projections of nerve cells, nerve fibers or axons.

The anterior lobe is controlled by the hypothalamus and it does so by releasing the hormones through the blood vessels and the posterior lobe controls it through the nerve impulses.

The hormones produced by the pituitary gland are not all produced continuously.

The pituitary gland can control the release of hormones every 1 to 3 hours or with alternating periods of activity and inactivity.

Some hormones, follow a circadian rhythm: the levels increase and decrease during the day, reaching the maximum point, before the awakening and reaching the minimum levels before sleeping.

The levels of other hormones also vary during the menstrual cycle such as luteinizing hormone and follicle stimulating hormone, which control reproductive functions.

Hormones of the anterior lobe

The anterior lobe of the hypophysis secretes six major hormones:

  • Growth hormone, which regulates growth and physical development and has important effects on body shape by stimulating muscle formation and reducing adipose tissue.
  • Thyroid stimulating hormone, which stimulates the thyroid gland to produce thyroid hormones.
  • Adrenocorticotropic hormone, also called corticotropin , which stimulates the adrenal glands to produce cortisol and other hormones.
  • The follicle-stimulating hormone and luteinizing hormone (gonadotropins), which stimulate the testes to produce sperm and the ovaries to produce eggs and sexual organs to produce sex hormones (testosterone and estrogen).
  • Prolactin, which stimulates the mammary glands of the breasts to produce milk.
  • The beta- melanocyte- stimulating hormone that causes darkening of the skin.
  • The enkephalins and endorphins, which inhibit the sensations of pain and stimulate the immune system.

Hormones of the posterior lobe

The posterior lobe produces two hormones:

  1. Vasopressin, which regulates the excretion of fluid in the kidneys and therefore controls the body’s water balance.
  2. Oxytocin, which controls contractions of the uterus during and after delivery, to prevent excessive bleeding, also stimulates the contractions that move breast milk to the nipple.

Disorders of the pituitary gland

The pituitary gland may present functioning problems, usually as a result of developing a noncancerous tumor (adenoma).

The tumor may encourage overproduction or a deficient production of one or more hormones, when it puts pressure on the normal cells of the pituitary gland.

The tumor can also cause enlargement of the pituitary gland.

Sometimes, excess cerebrospinal fluid can fill the space around the pituitary gland and compress it, causing the empty chair syndrome.

The pressure can cause the pituitary to modify the level of production of the hormones.

symptom

The production of too small or too many hormones produces a wide variety of symptoms.

The disorders that result from the overproduction of hormones include:

  • Acromegaly or gigantism: growth hormone.
  • Galactorrhea: the secretion of breast milk by men or by women when they are not pregnant.
  • Erectile dysfunction: prolactin.

Disorders resulting from the underproduction of hormones include:

  • Central insipidal diabetes: vasopressin.
  • Hypopituitarism : multiple hormones.

Diagnosis

Doctors can diagnose the malfunction of the pituitary gland by several tests.

Imaging tests, such as computed tomography or magnetic resonance imaging, can show if the pituitary gland has enlarged or shrunk.

Such tests can usually determine if there is a tumor in the gland.

It is possible to measure hormone levels, usually by a simple blood test.

The medical specialists select which levels of hormones they want to measure according to the person’s symptoms.

Sometimes, hormone levels are not easy to interpret because the levels vary a lot during the day and according to the requirements of the organisms.

To measure some of these hormones, it is necessary to administer some substances that would normally affect the production of hormones, such as insulin, which affects the levels of the adrenocorticotropic hormone, growth hormone and prolactin for these reasons, interpreting the results of blood tests for Hormones is very complex.