The pituitary gland is a small oval endocrine gland that lies at the base of the brain. It is sometimes called the master gland of the body because all the other endocrine glands depend on its secretions for stimulation.
Functionally speaking, the pituitary is divided into two distinct lobes that arise from different embryological sources. The anterior (front) lobe, or adenohypophysis, grows upward from the pharyngeal tissue at the roof of the mouth. The posterior (back) lobe, or neurohypophysis, grows downward from neural tissue. It is structurally continuous with the hypothalamus of the brain, to which it remains attached by the hypophyseal, or pituitary, stalk. The hypothalamus controls almost all secretions of the pituitary. The posterior lobe is controlled by nerve fibers that originate in hypothalamic neurons and the anterior lobe by substances that are transported from the hypothalamus by tiny blood vessels (see image below).
Hormones
Hormones are chemicals which circulate in the blood stream and spread around the body to carry messages or signals to different parts of the body. The name hormone comes from the Greek word hormao meaning "I excite" and refers to the fact that each hormone excites or stimulates a particular part of the body known as the target gland.
Hormones are made in endocrineglands and passed from the cells of the gland directly into the blood flowing through the gland. Generally, the higher the amount of hormone that is in the blood, the greater the effect its the targets.
Hormones produced by the pituitary gland
The two sections of the pituitary gland produce a number of different hormones which act on different target glands or cells.
This diagram shows the relationship of the pituitary gland and the hypothalamus and the flow of hormone production.
Anterior Pituitary
Adrenocorticotrophic Hormone (ACTH)
Thyroid-Stimulating Hormone (TSH)
Luteinising Hormone (LH)
Follicle-Stimulating Hormone (FSH)
Prolactin (PRL)
Growth Hormone (GH)
Melanocyte-Stimulating Hormone (MSH)
Posterior Pituitary
Anti-Diuretic Hormone (ADH)
Oxytocin
The tissues in the anterior lobe secrete at least six different hormones. Growth hormone stimulates all the tissues in the body to grow by effecting protein formation.
The remaining five important hormones influence body functions by stimulating target organs. Adrenocorticotropic hormone (ACTH) controls the secretion of steroid hormones by the adrenal cortex, which affects glucose, protein, and fat metabolism; thyrotropin controls the rate of thyroxine synthesis by the thyroid gland, which is the principal regulator of body metabolic rate; prolactin, which regulates the formation of milk after the birth of an infant; and three separate gonadotropic hormones (follicle-stimulating hormone, luteinizing hormone, and luteotropic hormone) control the growth and reproductive activity of the gonads.
The release of each of the hormones from the anterior lobe is controlled by a specific substance secreted by nerve cells in the hypothalamus. These substances, called releasing factors, are transmitted by nerve fibers to tiny capillaries in the hypophyseal stalk. They move through blood vessels to the anterior lobe, where each releasing factor is responsible for the release of a specific pituitary hormone.
The two hormones that are produced by the posterior lobe, anti-diuretic hormone (ADH), and oxytocin, are synthesized by nerve cells in the hypothalamus. They are transported by nerve fibers to nerve endings in the posterior lobe, where they are released. Antidiuretic hormone (ADH or vasopressin), alters the permeability of the kidney tubules, permitting more water to be retained by the body. Oxytocin, which aids in the release of milk from mammary glands and causes uterine contractions. The only hormone that is synthesized by the intermediate lobe is the melanocyte-stimulating hormone, which appears to control skin pigmentation.
Stimulates the adrenal gland to produce a hormone called cortisol. ACTH is also known as corticotrophin.
TSH
Thyroid
Stimulates the thyroid gland to secrete its own hormone, which is called thyroxine. TSH is also known as thyrotrophin.
LH & FSH
Ovaries (Women) Testes (Men)
Controls reproductive functioning and sexual characteristics. Stimulates the ovaries to produce estrogen and progesterone and the testes to produce testosterone and sperm. LH and FSH are known collectively as Gonadotrophins. LH is also referred to as Interstitial cell stimulating hormone (ICSH) in males.
PRL
Breasts
Stimulates the breasts to produce milk. This hormone is secreted in large amounts during pregnancy and breastfeeding, but is present at all times in both men and women.
GH
All cells in the body
Stimulates growth and repair. Research is currently being carried out to identify the functions of GH in adult life.
MSH
Exact role in humans unknown, but increases skin pigmentation in amphibians.
ADH
Kidneys
Controls the blood fluid and mineral levels in the body by affecting water retention by the {kidney} kidneys. This hormone is also known as vasopressin or arginine vasopressin (AVP).
The secretion of hormones from the anterior pituitary is controlled by the production of hormones by the hypothalamus. Although there are a number of different hormones they can be split into two main types:
hormones that tell the pituitary to switch on production of a hormone (a releasing hormone); and
hormones that tell the pituitary to switch off production of a hormone (an inhibiting hormone).
The hormones secreted by the posterior pituitary are produced in the hypothalamus and then passed down a tube between the hypothalamus and the pituitary (the pituitary stalk) when they are then secreted into the blood.
In total more than 200 hormones or hormone-like substances have been discovered. In addition to the hormones listed in the table above, five of these hormones are controlled by hormones released by the pituitary.
Table of Hormones Under the Control of the Pituitary Gland
Hormone
Organ
Function
Cortisol
Adrenals
Cortisol has a number of functions. It promotes normal metabolism; maintains blood sugar levels and blood pressure; provides resistance to stress and acts as an anti-inflammatory agent. It also plays a part in regulation of fluid balance in the body.
Thyroxine
Thyroid
Thyroxine controls many body functions, including heart rate, temperature and metabolism. It also plays a role in the metabolism of calcium in the body.
Estrogen
Ovaries
Estrogen facilitates growth of the tissues of the sex organs and other tissues related to reproduction. Estrogen also acts to strengthen bones and has a protective effect on the heart.
Progesterone
Ovaries
Progesterone promotes the changes in the uterus that occur in preparation for the implantation of a fertilized ovum and prepares the breasts for milk production.
Testosterone
Testes
Testosterone is responsible for the characteristics of the masculine body, including hair growth on the face and body and muscle development. Testosterone is essential for the production or sperm and also acts to strengthen bones.
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