40. PITUITARY GLAND

Pituitary Gland

The pituitary gland (hypophysis) is a small but vital endocrine gland located beneath the brain in the sella turcica of the sphenoid bone. It is connected to the hypothalamus by a stalk-like structure called the infundibulum. The gland consists of two lobes derived from different embryological origins:

  • Anterior lobe (Adenohypophysis): Developed from ectodermic tissue of the roof of the mouth.
  • Posterior lobe (Neurohypophysis): Derived from ectodermic tissue of the floor of the brain.

Anterior Pituitary Gland (Adenohypophysis)

The hypothalamic hormones regulate the secretion of adenohypophyseal hormones. Although not directly connected to the hypothalamus, the two communicate through a portal circulatory system.

The anterior pituitary secretes several important hormones that regulate a wide range of body activities, particularly influencing other endocrine glands (called tropic or tropic hormones).

Hormones Secreted by Adenohypophysis

  1. Human Growth Hormone (HGH or Somatotrophin):
    • Promotes growth of tissues, bones, and muscles.
    • Stimulates protein synthesis, reduces glucose use for ATP, and promotes fat metabolism.
    • Regulated by Growth Hormone Releasing Hormone (GHRH) and Growth Hormone Inhibiting Hormone (GHIH).
    Disorders: Hyposecretion causes pituitary dwarfism; hypersecretion in childhood causes gigantism, and in adults causes acromegaly.
  2. Thyroid Stimulating Hormone (TSH or Thyrotrophin): Stimulates synthesis and release of thyroid hormones (T3 and T4) from the thyroid gland. Controlled by thyrotrophic releasing hormone from the hypothalamus.
  3. Follicle Stimulating Hormone (FSH):
    • Stimulates ovarian follicle development and estrogen secretion in females.
    • In males, promotes sperm development (spermatogenesis).
    • Controlled by hypothalamic gonadotropin releasing hormone (GnRH).
  4. Luteinizing Hormone (LH):
    • Stimulates ovulation and formation of corpus luteum in females.
    • Stimulates secretion of progesterone and estrogen in females, and testosterone in males.
    • Also referred to as Interstitial Cell Stimulating Hormone (ICSH) in males.
  5. Prolactin (PRL):
    • Initiates and maintains milk production by mammary glands.
    • Stimulated by Prolactin Releasing Hormone (PRH) and inhibited by Prolactin Inhibitory Hormone (PIH).
    • Highest levels occur during pregnancy and lactation.
  6. Adrenocorticotropic Hormone (ACTH): Regulates secretion of glucocorticoids by the adrenal cortex. Stimulated by Corticotrophin Releasing Hormone (CRH) during stress or hypoglycemia.
  7. Melanocyte Stimulating Hormone (MSH): Increases skin pigmentation in some animals; its role in humans is not well understood.

Posterior Pituitary Gland (Neurohypophysis)

The posterior pituitary releases two main hormones — Antidiuretic Hormone (ADH) and Oxytocin. These are produced by neurosecretory cells in the hypothalamus and transported to the pituitary via a carrier protein called neurophysin.

Hormones of Neurohypophysis

  1. Antidiuretic Hormone (ADH or Vasopressin):
    • Promotes water reabsorption in the kidney tubules, reducing urine output.
    • Maintains body fluid balance and causes vasoconstriction, increasing blood pressure.
    • Secretion is regulated by body hydration levels and osmoreceptors in the hypothalamus.
  2. Oxytocin:
    • Stimulates uterine contractions during childbirth.
    • Triggers milk ejection (“let-down reflex”) during breastfeeding.
    • Released in response to nerve impulses during labor and nipple stimulation.

Note: The roles of oxytocin in males and non-pregnant females are not fully understood.

Detailed Notes:

For PDF-style full-color notes, open the complete study material below.

PATH: PHARMD/ PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ HUMAN ANATOMY AND PHYSIOLOGY/ PITUITARY GLAND.

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