Pituitary Gland- The Master Gland
The pituitary gland is also called as hypophysis or Master Gland. This is known as master gland as it not only secretes many hormones but also regulates the function of other hormone-secreting glands. It releases nine important hormones – ACTH (Adrenocorticotrophic hormone), TSH (Thyroid Stimulating Hormone), LH (Luteinising Hormone), FSH (Follicle Stimulating Hormone), PRL (Prolactin), GH (Growth hormone), MSH (Melanocyte Stimulating hormone), ADH (Antidiuretic Hormone), Oxytocin. Hence it can be concluded why pituitary gland is the master gland. All are peptide hormones which bind to membrane (extracellular) receptors. Most of them use cyclic-AMP as the second messenger.
▶The Location and Anatomy of the Pituitary Gland
The hypothalamus is a small region present directly above the brain stem. This manipulates the hormone release by controlling the pituitary gland.
The pituitary gland is present just below the hypothalamus. It lies at the base of the brain. It is of the size of a pea. There are various nerves surrounding the gland-like the nerve that control the sense of smell, on the top of the pituitary gland there is the presence of nerves of vision. This gland is nestled between the temporal lobes. The pituitary gland connects to the rest of the brain using the pituitary stalk (infundibulum) which sends electrical signals to the hormones down the gland.
The pituitary gland consists of two lobes namely the anterior pituitary gland secreting 7 hormones and posterior pituitary secreting 2 hormones.
▶Anterior Pituitary Gland
It is controlled by regulatory hormones from hypothalamic neurons. The hypophyseal portal system transports hypothalamic hormones directly to anterior pituitary target cells. It is regulated by negative feedback control.
Thyroid-Stimulating Hormone (TSH)
• Triggers thyroid hormone release, called thyroxine.
Adrenocorticotropic Hormone (ACTH)
• Stimulates glucocorticoid release from the adrenal gland
Follicle-Stimulating Hormone (FSH)
• Stimulates estrogen secretion, egg production (females), sperm production (males)
Luteinizing Hormone (LH)
• Triggers ovulation, progestin production (females), androgen production (males). It is also known as interstitial cell-stimulating hormone (ICSH)
LH and FSH are collectively known as gonadotrophins.
• Stimulates mammary gland development and milk secretion
Growth hormone (GH)
• Stimulates cell growth via somatomedins released from liver
Posterior Pituitary Gland
Releases hormones from hypothalamic axons
Antidiuretic Hormone (ADH)
• Reduces water loss in the urine
• Increases thirst
• Stimulates uterine contraction, milk delivery
• Stimulates prostate gland smooth muscle