The human body

How does the pituitary gland work?

The pituitary gland regulates various body functions and plays an important role in balancing hormone levels in the body. It is a protrusion at the base of the brain and about the size of a pea or cherry. The gland lies well protected in a small bony cavity of the skull, level with the eyes, and roughly in the middle of the head.

Illustration: Pituitary gland – Location and individual parts, as described in the articleThe pituitary gland: Location and individual parts

Together with the hypothalamus – which belongs to a part of the brain known as the diencephalon – the pituitary gland controls the involuntary (vegetative) nervous system. This part of the nervous system manages the balance of energy, heat and water in the body, which includes things like body temperature, heartbeat, urination, sleep, hunger and thirst. The pituitary gland also produces a number of hormones that either regulate 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, each with their own functions:

  • Anterior lobe
  • Posterior lobe
  • The part that joins the two lobes (pars intermedia)
  • Pituitary stalk, which forms the connection to the diencephalon

Anterior lobe

The anterior lobe makes up about three quarters of the overall mass of the pituitary gland. It produces two kinds of hormones:

  1. Hormones that control other hormone-producing glands
  2. Hormones that have a direct effect on the body

The group of hormones that control glands includes:

  • Thyroid-stimulating hormone (TSH): regulates hormone production in the thyroid gland.
  • Adrenocorticotropic hormone (ACTH): stimulates the adrenal glands to produce hormones such as adrenalin (epinephrine) or steroids.
  • Follicle-stimulating hormone (FSH): regulates hormone production in the ovaries and testicles.
  • Luteinizing hormone (LH): 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): has an effect in many parts of the body – particularly the liver, bones, fat tissue and muscle tissue.
  • Prolactin: influences the mammary glands and ovaries.

The hormones are released into the bloodstream by the pituitary gland and then travel through the blood vessels until they reach the various organs they have an effect on. TSH, for example, stimulates the thyroid gland to increase or reduce the production of thyroid hormones, depending on how much is needed. Prolactin stimulates the growth of girls’ mammary glands in puberty, suppresses ovulation in pregnant women, and triggers the production of breast milk after giving birth.

The production of hormones in the anterior lobe itself is regulated in two ways:

  • Through the hypothalamus, which makes hormones (known as “releasing hormones”) that increase the production of hormones in the anterior lobe or hormones (known as “inhibiting hormones”) that reduce it.
  • Through hormone levels in the blood: For instance, if the level of thyroid hormones in the body is high enough, the pituitary gland stops producing the hormone that stimulates the thyroid gland. This works the other way round, too: If the level of thyroid hormones is too low, the pituitary gland and hypothalamus increase the production of thyroid-stimulating hormone. The thyroid gland then produces more thyroid hormones.

Posterior lobe

The posterior lobe of the pituitary gland mainly consists of entangled nerve fibers coming from the hypothalamus. Two different hormones are stored in the posterior lobe. They are released if needed:

  • Oxytocin: affects the womb and mammary glands, and causes contractions in childbirth, for instance.
  • Antidiurietic hormone (ADH): regulates water uptake in the kidneys and makes the blood vessels narrower.

The posterior lobe of the pituitary gland is directly connected to the hypothalamus through the pituitary stalk.

Intermediate part (pars intermedia)

Hormone-producing tissue is found between the anterior and posterior pituitary, too. Melanocyte-stimulating hormones (MSH) are produced in this intermediate part of the pituitary gland. They stimulate the production of things like melanin in the skin. Melanin is a pigment that protects against harmful ultraviolet sun rays. MSH also regulates our appetite and influences our sex drive.