Memory tricks for glands and hormones

Hypothalamus (brain base) — master controller, releases releasing/inhibiting hormones. Pituitary (sella turcica of sphenoid) — master gland, two lobes. Pineal (brain) — melatonin, circadian rhythm. Adrenal (atop kidneys) — cortex and medulla. Thyroid (anterior neck) — metabolism. Parathyroid (posterior thyroid, 4 glands) — calcium. Pancreas (retroperitoneal) — blood sugar. Thymus (mediastinum) — T-cell maturation. Gonads (testes/ovaries) — sex hormones.

FSH (follicle stimulating hormone): follicle development and spermatogenesis. LH (luteinizing hormone): ovulation and testosterone production. ACTH (adrenocorticotropic hormone): stimulates adrenal cortex to produce cortisol. TSH (thyroid stimulating hormone): stimulates thyroid to produce T3/T4. Prolactin: milk production. GH (growth hormone): stimulates growth and IGF-1 production. The posterior pituitary stores and releases ADH and oxytocin — but does NOT produce them (they are made in the hypothalamus).

T4 (thyroxine) is the main secreted hormone — converted to T3 (triiodothyronine) in peripheral tissues. T3 is 3-4× more potent. Both require iodine — deficiency causes goiter (enlarged thyroid). Calcitonin is produced by parafollicular C cells — lowers blood calcium by inhibiting osteoclasts. Hypothyroidism: low metabolism, weight gain, cold intolerance, fatigue, constipation. Hyperthyroidism: high metabolism, weight loss, heat intolerance, tachycardia, exophthalmos (in Graves' disease).

The adrenal cortex has three zones from outside to inside. Zona Glomerulosa (outer) → mineralocorticoids (aldosterone) — Salt. Zona Fasciculata (middle) → glucocorticoids (cortisol) — Sugar. Zona Reticularis (inner) → androgens (DHEA) — Sex. Memory trick: GFR from outside in, and "Salt Sugar Sex — the deeper you go." Addison's disease = adrenal insufficiency (low cortisol and aldosterone). Cushing's syndrome = excess cortisol (moon face, buffalo hump, striae).

Insulin (beta cells) released when blood glucose rises after a meal → glucose enters cells, glycogen synthesis, fat storage. Lowers blood glucose. Glucagon (alpha cells) released when blood glucose falls → glycogenolysis (breaks down glycogen), gluconeogenesis (makes new glucose). Raises blood glucose. Type 1 diabetes: no insulin (autoimmune destruction of beta cells). Type 2 diabetes: insulin resistance — cells don't respond. Both result in hyperglycemia but through different mechanisms.

PTH (parathyroid hormone): released when calcium is LOW. Raises calcium by activating osteoclasts (bone resorption), increasing renal reabsorption of calcium, and activating vitamin D. Calcitonin (thyroid C cells): released when calcium is HIGH. Lowers calcium by inhibiting osteoclasts. Vitamin D (activated in kidneys from sunlight precursor): increases intestinal absorption of calcium. Hypoparathyroidism → hypocalcemia → tetany (muscle spasms). Hyperparathyroidism → hypercalcemia → stones, bones, groans, psychic moans.

Most endocrine systems use negative feedback — the product inhibits its own production. Example: Low thyroid hormone → hypothalamus releases TRH → pituitary releases TSH → thyroid produces T3/T4 → high T3/T4 feeds back to inhibit TRH and TSH release. The thermostat analogy: when the room is warm enough, the heater turns off. Understanding negative feedback explains virtually every endocrine lab interpretation — high TSH + low T4 = hypothyroidism. Low TSH + high T4 = hyperthyroidism.

Cortisol is released by the adrenal cortex in response to ACTH and stress. Blood sugar: raises glucose via gluconeogenesis — breaks down protein and fat for fuel. Immunity: suppresses immune response — why corticosteroids are used for inflammation but increase infection risk. Decreased inflammation: stabilizes cell membranes, reduces prostaglandins. Everything broken down: catabolic — muscle wasting, bone loss, thin skin with prolonged excess. Diurnal rhythm: peaks at 8 AM, lowest at midnight. Stress response essential for survival.

The adrenal medulla is essentially modified postganglionic sympathetic neurons — it releases epinephrine (80%) and norepinephrine (20%) directly into the bloodstream. Epinephrine: increases HR, bronchodilation, blood glucose (glycogenolysis), dilates skeletal muscle vessels. Norepinephrine: primarily vasoconstriction, increases BP. Both prepare the body for fight or flight. Pheochromocytoma = adrenal medulla tumor → excess catecholamines → hypertensive crises, headache, palpitations, sweating (the classic triad).