It is a pea-sized gland found within a bony structure called a Turkish chair, located at the base of the brain.
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.
The pituitary gland has two distinct parts:
- The frontal or anterior lobe 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 hypothalamus controls the anterior lobe, 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 important hormones:
- Growth hormone regulates growth and physical development and significantly affects body shape by stimulating muscle formation and reducing adipose tissue.
- Thyroid-stimulating hormone stimulates the thyroid gland to produce thyroid hormones.
- Adrenocorticotropic hormone, also called corticotropin, stimulates the adrenal glands to produce cortisol and other hormones.
- The follicle-stimulating hormone and luteinizing hormone (gonadotropins) stimulate the testes to produce sperm, the ovaries to produce eggs, and sexual organs to produce sex hormones (testosterone and estrogen).
- Prolactin stimulates the mammary glands of the breasts to produce milk.
- The beta- melanocyte-stimulating hormone causes the darkening of the skin.
- The enkephalins and endorphins inhibit pain sensations and stimulate the immune system.
Hormones of the posterior lobe
The posterior lobe produces two hormones:
- Vasopressin regulates fluid excretion in the kidneys and controls the body’s water balance.
- 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 due to developing a noncancerous tumor (adenoma).
The tumor may encourage overproduction or 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.
The production of too small or too many hormones produces various 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 women when they are not pregnant.
- Erectile dysfunction: prolactin.
Disorders resulting from the underproduction of hormones include:
- Central insipid diabetes: vasopressin.
- Hypopituitarism: multiple hormones.
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.