Hypothalamus and Pituitary Gland

Hypothalamus & Pituitary Anatomy - Brain's Tiny Bosses

• Hypothalamus: Located at the base of the brain, superior to the pituitary gland. Connected to pituitary via the infundibulum (stalk).
• Pituitary Gland (Hypophysis): Rests in the sella turcica of the sphenoid bone.
  • Anterior Lobe (Adenohypophysis):
    • Origin: Rathke's pouch (oral ectoderm).
    • Vascular link: Hypophyseal portal system from hypothalamus.
  • Posterior Lobe (Neurohypophysis):
    • Origin: Downgrowth of neural ectoderm from hypothalamus.
    • Stores & releases: ADH and Oxytocin (synthesized in hypothalamus).

⭐ The posterior pituitary (neurohypophysis) is an extension of the hypothalamus, not a true gland, as it stores and releases hormones produced in hypothalamic nuclei (supraoptic and paraventricular).

Hypothalamic Hormones - Pituitary's Puppeteers

• Control: Hypothalamus directs pituitary.
  • • Anterior Pituitary (AP): Via releasing/inhibiting hormones through hypophyseal portal system.
  • • Posterior Pituitary (PP): Via neuronal axons; stores & releases hypothalamic ADH/Oxytocin.
• AP Releasing Hormones (+):
  • • TRH: ↑TSH, ↑PRL
  • • CRH: ↑ACTH
  • • GnRH: ↑FSH, ↑LH

    ⭐ Pulsatile GnRH vital for FSH/LH; continuous GnRH inhibits (therapeutic use).

  • • GHRH: ↑GH
• AP Inhibiting Hormones (-):
  • • Somatostatin (GHIH): ↓GH, ↓TSH
  • • Dopamine (PIH): ↓PRL (tonic inhibition)
• PP Hormones (Synthesized in Hypothalamus):
  • • ADH (Vasopressin): Supraoptic Nucleus (SON).
  • • Oxytocin: Paraventricular Nucleus (PVN).

Anterior Pituitary Hormones - Master Gland's Crew

📌 Mnemonic: FLAT PEG (FSH, LH, ACTH, TSH, Prolactin, GH)

• GH (Somatotropin): Stimulates growth (linear, muscle) via IGF-1. Targets: Liver, bone, muscle. Reg: GHRH (+), Somatostatin (-).
• PRL (Prolactin): Milk production, breast development. Target: Mammary glands. Reg: Dopamine (-), TRH (+).
• ACTH (Corticotropin): From POMC. Stimulates adrenal cortex (cortisol, aldosterone, androgens). Reg: CRH (+).
• TSH (Thyrotropin): Stimulates thyroid (T3, T4 synthesis/release). Reg: TRH (+), Somatostatin (-).
• Gonadotropins (FSH, LH): Reg: GnRH (+).
  • FSH: ♀: Follicle growth, estrogen. ♂: Spermatogenesis (Sertoli).
  • LH: ♀: Ovulation, progesterone. ♂: Testosterone (Leydig).

⭐ Prolactin secretion is tonically inhibited by dopamine from the hypothalamus. Dopamine antagonists (e.g., antipsychotics) can cause hyperprolactinemia.

Posterior Pituitary Hormones - Hypothalamus's Direct Line

• Synthesized in Hypothalamus, stored & released from Posterior Pituitary (Neurohypophysis).
  • ADH (Vasopressin): Mainly Supraoptic Nucleus (SON). Water reabsorption (kidney V2 receptors).
  • Oxytocin: Mainly Paraventricular Nucleus (PVN). Milk ejection, uterine contraction.
• Posterior pituitary is a release site, not a synthesis site.

  ⭐ Central Diabetes Insipidus: Deficient ADH secretion. Leads to polyuria, polydipsia, dilute urine (specific gravity < 1.005).

Key Pituitary Disorders - Hormonal Havoc

• Acromegaly/Gigantism: ↑GH. Adults: coarse facies, large extremities. Children: gigantism.
• Cushing's Disease: Pituitary adenoma → ↑ACTH. Central obesity, moon facies, purple striae.
• Prolactinoma: Most common. ↑Prolactin → galactorrhea, amenorrhea, infertility.
• Diabetes Insipidus (Central): ↓ADH. Intense thirst, polyuria, dilute urine.
• SIADH: ↑ADH. Euvolemic hyponatremia, concentrated urine.
• Hypopituitarism: Deficiency of ≥1 hormones. Sheehan's syndrome (postpartum necrosis).

⭐ Nelson's syndrome: Rapid enlargement of pituitary adenoma post-bilateral adrenalectomy for Cushing's disease.

High‑Yield Points - ⚡ Biggest Takeaways

• Anterior pituitary is controlled by hypothalamic releasing/inhibiting hormones.
• Posterior pituitary releases ADH & oxytocin, synthesized in the hypothalamus.
• Prolactin secretion is tonically inhibited by hypothalamic dopamine.
• GH excess leads to acromegaly/gigantism; deficiency to dwarfism.
• ADH deficiency causes Central Diabetes Insipidus (polyuria, dilute urine).
• Sheehan's syndrome: postpartum pituitary necrosis leading to panhypopituitarism.
• Craniopharyngioma: common suprasellar tumor with calcifications, may cause hypopituitarism.