The hypothalamus and pituitary gland form a crucial neuroendocrine axis that regulates growth, metabolism, reproduction, stress, and lactation. Hormones released from the hypothalamus stimulate or inhibit the secretion of specific hormones from the anterior and posterior pituitary.
Major Hypothalamic–Pituitary Hormones and Their Functions
| Hormone | Primary Function | Clinical Notes / Key Concepts |
|---|---|---|
| ADH (Vasopressin) | ↑ Water permeability in the distal convoluted tubule and collecting ducts → ↑ water reabsorption | ↓ by alcohol, causing polyuria and dehydration |
| CRH (Corticotropin-Releasing Hormone) | ↑ ACTH, MSH, and β-endorphin secretion | ↓ in chronic glucocorticoid use |
| Prolactin-Inhibiting Factor (Dopamine) | ↓ Prolactin and ↓ TSH secretion | Dopamine antagonists (e.g., antipsychotics) → ↑ prolactin → galactorrhea, amenorrhea |
| GHRH (Growth Hormone-Releasing Hormone) | ↑ GH secretion | Analog Tesamorelin is used for HIV-associated lipodystrophy |
| GnRH (Gonadotropin-Releasing Hormone) | ↑ FSH and LH secretion | Suppressed by hyperprolactinemia Pulsatile GnRH → puberty, fertility Continuous GnRH analog (e.g., Leuprolide) → suppresses HPG axis |
| MSH (Melanocyte-Stimulating Hormone) | ↑ Melanin synthesis by melanocytes | ↑ MSH causes hyperpigmentation in Cushing’s disease (shares precursor POMC with ACTH) |
| Oxytocin | Causes uterine contractions during labor; triggers milk letdown during breastfeeding | Also modulates fear, anxiety, social bonding, and mood |
| Prolactin | ↓ GnRH secretion promotes lactogenesis | ↑ Prolactin (e.g., prolactinoma) → amenorrhea, osteoporosis, galactorrhea, hypogonadism Breastfeeding ↑ prolactin → ↓ GnRH → delayed ovulation (natural contraception) |
| Somatostatin (GHIH) | ↓ GH and ↓ TSH secretion | Also called Growth Hormone-Inhibiting Hormone; secreted by delta cells of the pancreas |
| TRH (Thyrotropin-Releasing Hormone) | ↑ TSH and ↑ Prolactin | ↑ TRH in primary/secondary hypothyroidism may cause galactorrhea (via ↑ prolactin) |
Additional Notes
| Hormone Class | Produced In | Major Control Mechanism |
|---|---|---|
| Peptide hormones (e.g., ACTH, GH, TSH, etc.) | Anterior pituitary | Hypothalamic releasing/inhibiting hormones |
| Neurohormones (e.g., ADH, Oxytocin) | Hypothalamus (supraoptic & paraventricular nuclei) | Released by the posterior pituitary via neurophysins |
Clinical Correlations
| Condition | Pathophysiology | Key Manifestation |
|---|---|---|
| Diabetes insipidus | ↓ ADH secretion or response | Polyuria, dehydration |
| Cushing disease | ↑ ACTH from the pituitary | Hyperpigmentation (↑ MSH) |
| Prolactinoma | Pituitary adenoma → ↑ prolactin | Amenorrhea, galactorrhea |
| Acromegaly | Excess GH (often from a tumor) | Enlarged hands, jaw, and organs |
| Sheehan syndrome | Postpartum pituitary necrosis | Failure to lactate, amenorrhea |
Learning Objectives
By the end of this topic, a medical student should be able to:
- Identify the major hypothalamic and pituitary hormones and their functions.
- Describe feedback mechanisms regulating hormone release.
- Correlate clinical syndromes with hormone excess or deficiency.
- Understand how drugs (e.g., dopamine antagonists, GnRH analogs) affect pituitary function.
