How does the pituitary gland work?

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

• Hormones that control other hormone-producing glands
• Hormones that have a direct effect on the body

The hormones that control glands include:

• 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 hormones that have a direct effect include:

• 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 (breast) 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 make more of thyroid-stimulating hormone. The thyroid gland then produces more thyroid hormones.

The posterior lobe of the pituitary gland mainly consists of 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.

The tissue between the anterior and posterior lobes also makes hormones. Melanocyte-stimulating hormones (MSH) are produced in this intermediate lobe. They stimulate the production of things like melanin in the skin. Melanin is a pigment that protects against harmful ultraviolet sun rays. MSH also controls our appetite and affects our sex drive.