Anatomy of the Pituitary Gland

The pituitary gland is a pea-sized gland that acts as the master gland of the endocrine system.

  • Location: It is securely located in a bony cavity of the skull called the sella turcica.
  • Connection: It is attached to the hypothalamus by a thin stalk called the infundibulum.

It is anatomically divided into two major portions:

1. Adenohypophysis (Anterior Pituitary)

This is the true glandular part. It consists of two portions:

  • Pars distalis: This is the major region, commonly called the 'anterior pituitary'.
  • Pars intermedia: A small intermediate zone. Important Note for NEET: In humans, this region is almost merged with the pars distalis.

2. Neurohypophysis (Posterior Pituitary)

  • Also known as the Pars nervosa.
  • Crucial Fact: It does NOT synthesize any hormones of its own. It only stores and releases hormones that are actually synthesized by the hypothalamus and brought down via axons.

Hormones of Adenohypophysis

The adenohypophysis is the glandular part of the pituitary. It is further divided into:

1. Pars Distalis (Anterior Pituitary)

Produces six major peptide hormones:

  1. Growth Hormone (GH): Stimulates overall body growth and protein synthesis.
    • Over-secretion (Childhood): Leads to Gigantism (abnormal increase in height).
    • Low secretion (Childhood): Leads to pituitary Dwarfism (stunted growth).
    • Acromegaly: Excess secretion of GH in adults (especially middle age). It leads to severe disfigurement (especially of the face, hands, and feet) and can lead to premature death if unchecked.
  2. Prolactin (PRL): Regulates the growth of mammary glands and the formation (synthesis) of milk in them.
  3. Thyroid Stimulating Hormone (TSH): Stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.
  4. Adrenocorticotrophic Hormone (ACTH): Stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.
  5. Luteinizing Hormone (LH):
    • Males: Stimulates the synthesis and secretion of androgens (like testosterone) from the testis.
    • Females: Induces ovulation of fully mature follicles (Graafian follicles) and maintains the corpus luteum (the remnant of the follicle after ovulation).
  6. Follicle Stimulating Hormone (FSH):
    • Males: Regulates spermatogenesis (along with androgens).
    • Females: Stimulates the growth and development of ovarian follicles.
    • Note: Because LH and FSH target the gonads, they are collectively called Gonadotrophins.

2. Pars Intermedia

Secretes only one hormone:

  • Melanocyte Stimulating Hormone (MSH): Acts on melanocytes (melanin-containing cells) and regulates the pigmentation of the skin.

Hormones of Neurohypophysis (Posterior Pituitary)

These hormones are synthesized in the hypothalamic nuclei and transported axonally to the neurohypophysis for storage and release:

  1. Oxytocin: Acts primarily on smooth muscles of our body, stimulating their contraction.
    • Females: Stimulates vigorous contraction of the uterus during childbirth (foetal ejection reflex) and the ejection of milk from the mammary gland.
  2. Vasopressin (Anti-Diuretic Hormone / ADH):
    • Acts mainly at the kidney.
    • Stimulates the resorption of water and electrolytes from the distal tubules (DCT) of the nephron.
    • Function: Reduces the loss of water through urine (prevents diuresis).
    • Disorder: Deficiency of ADH or receptor failure leads to Diabetes Insipidus, characterized by excessive water loss in urine and intense thirst.

The Pituitary Gland

1. Anterior Pituitary Hormones Mnemonic (FLAG PT):

  • FSH
  • LH
  • ACTH
  • GH
  • Prolactin
  • TSH

2. Prolactin vs. Oxytocin (The Milk Rule):

  • Prolactin = Production (Synthesizes milk).
  • Oxytocin = Oozing (Ejects milk out).

3. Vasopressin's Other Name: Vasopressin = ADH (Anti-Diuretic Hormone). Think "Anti-Peeing" hormone. It saves water by pulling it back into the blood from the kidneys. Without it, you get Diabetes Insipidus (tasteless, watery urine).

💡 Questions and Answers

Q1. Which hormone is responsible for the milk ejection reflex?

A1: The hormone responsible for the milk ejection reflex is Oxytocin. It helps in pushing milk out from the mammary glands after it has been produced.

Key points:

  • Oxytocin = milk ejection
  • Prolactin = milk production

Q2. What is the condition caused by excess secretion of Growth Hormone in adults?

A2: If Growth Hormone is secreted in excess in adults, it causes Acromegaly. In this condition, bones of the face, hands, and feet become abnormally enlarged.

Key points:

  • Excess GH in adults = Acromegaly
  • Excess GH in children = Gigantism

Q3. Name the two hormones collectively known as gonadotrophins.

A3: The two hormones called gonadotrophins are LH and FSH because they act on the gonads.

Key points:

  • LH + FSH = Gonadotrophins

Q4. Where is the pituitary gland located?

Answer (in my words): The pituitary gland is located in a bony cavity of the skull called the sella turcica.

Key points:

  • Location = sella turcica
  • Pituitary is attached to hypothalamus by a stalk

Q5. What is the primary function of ADH (Vasopressin)?

A5: The main function of ADH is to increase the reabsorption of water in the kidneys. This reduces water loss in urine and helps maintain water balance in the body.

Key points:

  • ADH acts on kidney
  • Increases water reabsorption
  • Reduces urine output