Makindo Medical Notes

The pituitary gland, often called the "master gland", regulates multiple physiological processes through hormone secretion. It sits at the base of the brain in the sella turcica, connected to the hypothalamus via the infundibulum. It has two main lobes: – Anterior Pituitary (Adenohypophysis) (glandular, larger) – Posterior Pituitary (Neurohypophysis) (neural, smaller)

🔬 Embryology

• Adenohypophysis (anterior) – derived from Rathke’s pouch (oral ectoderm).
• Neurohypophysis (posterior) – outgrowth of the hypothalamus, linked via the infundibular stalk.
• Separated by a pars intermedia.

⚡ Anterior Pituitary Hormones

• Growth Hormone (GH) – ↑ protein synthesis, lipolysis, cell growth.
• Prolactin (PRL) – stimulates milk production.
• Adrenocorticotropic Hormone (ACTH) – stimulates adrenal cortex → cortisol.
• Thyroid-Stimulating Hormone (TSH) – stimulates thyroid → T3/T4.
• Follicle-Stimulating Hormone (FSH) – gametogenesis (sperm, ova).
• Luteinizing Hormone (LH) – ovulation, sex hormone production (estrogen, progesterone, testosterone).

💡 Posterior Pituitary Hormones

• Antidiuretic Hormone (ADH, vasopressin) – water reabsorption in kidneys, vasoconstriction → ↑ BP.
• Oxytocin – uterine contractions, milk let-down, bonding/social behaviour.

⚙️ Regulation of Pituitary Hormones

• Hypothalamic releasing/inhibiting hormones: – TRH → TSH – CRH → ACTH – GnRH → FSH & LH – GHRH → GH (stimulated), Somatostatin → inhibits GH – Dopamine → inhibits prolactin
• Feedback loops: Negative feedback maintains balance. E.g. cortisol suppresses CRH + ACTH release.

🚨 Clinical Relevance

• Hypopituitarism – ↓ pituitary hormones. Causes: tumours, trauma, infection. Symptoms: fatigue, infertility, growth delay.
• Hyperpituitarism – ↑ hormone secretion, often adenoma. – Excess GH → acromegaly. – Excess ACTH → Cushing’s disease.
• Diabetes Insipidus – ADH deficiency → polyuria, polydipsia.
• SIADH – excess ADH → hyponatraemia, water retention. Causes: CNS disease, tumours, drugs.

📌 Summary

The pituitary regulates growth, metabolism, reproduction, water balance, and stress responses. Anterior pituitary → produces trophic hormones (GH, TSH, ACTH, FSH, LH, PRL). Posterior pituitary → stores/release ADH & oxytocin. Disorders can cause profound endocrine syndromes (e.g. acromegaly, DI, SIADH).

📝 Exam Pearls

• GH excess in children → gigantism; in adults → acromegaly.
• Prolactinoma = most common pituitary adenoma.
• ADH deficiency = Diabetes Insipidus (polyuria, polydipsia, dilute urine).
• SIADH = hyponatraemia with concentrated urine, low serum osmolality.
• Remember: dopamine inhibits prolactin (so dopamine antagonists → ↑ PRL).