Pituitary Gland

Overview and Anatomical Structure

The pituitary gland, often referred to as the "Master Gland," is a small but crucial endocrine organ located at the base of the brain. It consists of two distinct parts that arise from different embryological origins and have unique functions: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

• Anterior Pituitary (Adenohypophysis): Develops from an infolding of the oral ectoderm (Rathke's pouch) in the roof of the mouth. It migrates upward and separates from the oral cavity, associating with the neural portion of the pituitary.

• Posterior Pituitary (Neurohypophysis): Develops as a downward extension (diverticulum) from the neuroectoderm of the developing brain, remaining physically connected to the brain via the infundibulum.

• The two parts meet to form the complete pituitary gland, with the anterior portion composed of epithelial cells and the posterior portion of neural tissue.

Functional Significance

• The pituitary gland regulates the activity of several other endocrine glands, earning its title as the "Master Gland."

• It plays a central role in growth, metabolism, reproduction, and water balance.

Anterior Pituitary (Adenohypophysis)

Hormones of the Anterior Pituitary

The anterior pituitary produces six major protein-based hormones, all of which act through second messenger systems. Many of these hormones are termed tropic hormones (or have "tropin" in their names), indicating that they stimulate other endocrine glands.

• Growth Hormone (GH) / Somatotropin: Stimulates growth in most tissues, especially muscles and bones, by promoting amino acid uptake and protein synthesis.

• Thyroid Stimulating Hormone (TSH) / Thyrotropin: Acts specifically on the thyroid gland, stimulating the production and release of thyroid hormones.

• Adrenocorticotropic Hormone (ACTH) / Corticotropin: Stimulates the adrenal cortex to secrete glucocorticoid hormones (such as cortisol).

• Follicle Stimulating Hormone (FSH): In females, promotes growth and maturation of ovarian follicles; in males, stimulates sperm production.

• Luteinizing Hormone (LH): In females, triggers ovulation and formation of the corpus luteum; in males, stimulates interstitial cells in the testes to produce testosterone.

• Prolactin (PRL): Primarily acts on female mammary glands to stimulate milk production after childbirth. (Minimal function in males.)

All anterior pituitary hormones are protein-based and utilize second messenger signaling pathways.

Summary Table: Anterior Pituitary Hormones

Posterior Pituitary (Neurohypophysis)

Hormones of the Posterior Pituitary

The posterior pituitary does not synthesize hormones itself; instead, it stores and releases two hormones produced by the hypothalamus. Both are protein-based and act via second messenger systems.

• Antidiuretic Hormone (ADH) / Vasopressin: Promotes water reabsorption in the kidneys, reducing urine output and increasing blood volume and pressure. In some animals, it also causes vasoconstriction, further raising blood pressure.

• Oxytocin: Stimulates uterine contractions during labor and milk ejection (let-down) from mammary glands in females. (Minimal function in males.)

Summary Table: Posterior Pituitary Hormones

Key Concepts and Definitions

• Tropic Hormones: Hormones that stimulate other endocrine glands to secrete their hormones.

• Second Messenger System: A method of cellular signaling in which a hormone binds to a receptor on the cell surface, triggering a cascade of intracellular events (often involving cyclic AMP or Ca2+).

• Infundibulum: The stalk that connects the pituitary gland to the hypothalamus.

Example: Hormonal Regulation

• When the body needs to grow, the hypothalamus signals the anterior pituitary to release GH, which then stimulates tissues to grow and repair.

• During dehydration, the hypothalamus triggers the release of ADH from the posterior pituitary, causing the kidneys to conserve water.

Additional info:

• The pituitary gland is protected within the sella turcica, a bony cavity at the base of the skull.

• Disorders of pituitary function can lead to conditions such as gigantism, dwarfism, diabetes insipidus, and inappropriate lactation.