Pituitary Gland Health Article

Definition

The pituitary gland is located at the base of the brain and is part of the endocrine system. It is sometimes called the hypophysis, from two Greek words that mean "to grow beneath." The pituitary is responsible for the hormonal regulation of several body processes, including water retention, breast milk synthesis and release, human growth, and thyroid gland secretions.

Description

The pituitary is one of the most extensively researched glands in the endocrine system. In humans, it is located at the base of the brain just beneath the hypothalamus. There are three separate lobes (or sections) of the pituitary: the anterior lobe, the posterior lobe and the intermediate lobe. Therefore, it is sometimes considered as three different glands. In addition, there is a small stem called the pituitary stalk that connects the pituitary to the hypothalamus.

The pituitary gland is formed during early fetal development. An understanding of its formation explains its position in the endocrine system as well as its neurological importance. Early in the development of the fetus, a small sac of cells forms at the top of the oral cavity and moves upward. These cells are known as Rathke's pouch. At the same time, a small fold of neural tissue extends downward from the hypothalamus. During fetal development, the two structures continue to move toward each other; they meet and fuse to form the anterior (originally Rathke's pouch) and posterior (from the hypothalamus) lobes of the pituitary.

The hypothalamus, which is located just above the pituitary gland, is a region in the forebrain that is responsible for regulating all lobes of the pituitary. The pituitary releases, but does not necessarily synthesize, nine different hormones. Neurohormones are synthesized by the hypothalamus and transported to the posterior pituitary. The release of hormones from each lobe of the pituitary is regulated differently.

Anterior pituitary

The anterior pituitary is sometimes called the adenohypophysis. It constitutes about 80% of the pituitary by weight. The cells of the anterior pituitary act like true endocrine cells. Instead of containing neurons, the anterior pituitary receives chemical signals through the blood and releases hormones in response. It has a direct connection with the hypothalamus through blood vessels. Various cells in the anterior pituitary release the following hormones:

• Gonadotrophs release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
• Lactotrophs release prolactin (PRL).
• Corticotrophs release adrenocorticotropic hormone (ACTH).
• Somatotrophs release growth hormone (GH).
• Thyrotrophs release thyroid-stimulating hormone (TSH).

Posterior pituitary

The posterior pituitary is sometimes referred to as the neurohypophysis because it acts like an extension of the nervous system. As opposed to the anterior pituitary, which is connected to the hypothalamus via the circulatory system, the posterior pituitary receives nerve impulses from the same nerve cells that innervate the hypothalamus. The posterior pituitary releases oxytocin and antidiuretic hormone (ADH, or vasopressin).

Intermediate pituitary

The intermediate lobe is not a complete "lobe" in humans. Instead it is a simple structure comprised of just a few cells. The intermediate pituitary is an important structure in many lower vertebrates, but it has very little significance in humans. In lower vertebrates, the intermediate

KEY TERMS

Acromegaly—Abnormal enlargement of such parts of the body as the hands, face, head, and feet.

Adenohypophysis—Another name for the anterior lobe of the pituitary.

Antidiuretic hormone (ADH)—A hormone released by the posterior lobe of the pituitary gland that increases the absorption of water by the kidneys. It is also known as vasopressin.

Diabetes insipidus—A disorder characterized by increased urine production resulting from inadequate levels of ADH.

Gonadotropins—Hormones that affect the development or activity of the ovaries or testes.

Hypophysis—Another name for the pituitary gland.

Hypopituitarism—A condition produced by deficient activity of the anterior lobe of the pituitary gland. It is characterized by obesity, incomplete sexual maturation, and in extreme cases, dwarfism.

Hypothalamus—A region in the forebrain that regulates the functions of the autonomic nervous system by vascular communication. The hypothalamus governs the functions of both lobes of the pituitary gland.

Neurohypophysis—Another name for the posterior lobe of the pituitary.

Oxytocin—A hormone produced by the posterior pituitary that stimulates the movement of breast milk from the sacs in which the milk is produced to the larger ducts from which the milk is ejected.

Peptide—A compound containing two or more amino acids, in which the carboxyl group of one acid is linked to the amino group of the other.

Vasopressin—Another name for ADH.

pituitary releases melanocyto-stimulating hormone. This hormone stimulates the growth of melanocytes, which are cells that produce a dark pigment called melanin.

Function

The pituitary gland is an organ that is part of the endocrine system, along with many other glands and organs. It is regulated by the hypothalamus, and it in turn regulates the secretion of many different hormones that are essential to human health.