Source / episode info
- **Episode:**191
- **Title:**Divine Intervention Episode 191 – Updated USMLE Step 1 Endocrine Review Series 1 (Adrenals).
- **Published:**2019-12-11
- Source:Episode page
One-liner
This episode provides a comprehensive review of adrenal gland anatomy, covering the HPA axis regulation, differentiating primary vs. secondary adrenal insufficiency using specific testing (ACTH/Metyrapone), detailing congenital adrenal hyperplasia enzyme deficiencies, and reviewing the complex pharmacology of mineralocorticoids and glucocorticoids.
High-yield summary
- Adrenal Anatomy: The cortex has three zones: Zona Glomerulosa (Mineralocorticoids -> Aldosterone); Zona Fasciculata (Glucocorticoids -> Cortisol); Zona Reticularis (Androgens). The medulla is derived from neuroectoderm and contains chromaffin cells.
- Primary Adrenal Insufficiency (Addison's): Characterized by low cortisol, high ACTH, hyperpigmentation (due to POMC/MSH), hypotension, hyponatremia, hyperkalemia, metabolic acidosis, and Type 4 RTA. Treatment requires both glucocorticoids and mineralocorticoids (e.g., Fludrocortisone).
- CAH Diagnosis: The most common cause is 21-hydroxylase deficiency. Key findings include low cortisol and elevated precursors (e.g., 17OHP). Salt-wasting form presents in infancy with severe electrolyte abnormalities.
- ACTH Axis Testing: Low dose Dexamethasone Suppression Test (LDDST) helps differentiate causes of hypercortisolism: Cushing's Disease (pituitary adenoma) shows no suppression, while adrenal adenomas show no suppression; the source is differentiated by ACTH levels (high in pituitary, low in adrenal).
- Electrolyte Pearls: Aldosterone excess leads to hypokalemia and metabolic alkalosis. Corticosteroids increase WBC count by preventing margination and suppress immune function via inhibition of phospholipase A2.
Learning objectives
- Describe the embryological and histological differences between the adrenal cortex (three zones) and medulla.
- Outline the HPA axis feedback loop, identifying the roles of CRH, ACTH, and cortisol.
- Differentiate the clinical presentation, lab findings, and management strategies for primary vs. secondary/tertiary adrenal insufficiency.
- Apply knowledge of mineralocorticoid action to predict electrolyte imbalances (e.g., aldosterone excess -> hypokalemia).
- Interpret enzyme deficiencies in Congenital Adrenal Hyperplasia (CAH) based on the resulting hormonal shunting and clinical presentation.
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