High-Yield NEET Facts — Chemical Coordination — Summary

The hypothalamus is the master coordinator bridging the nervous and endocrine systems.
Anterior pituitary hormones (FLAT PG): FSH, LH, ACTH, TSH, Prolactin, GH — all made in the adenohypophysis.
Posterior pituitary: stores and releases ADH and oxytocin; both are synthesised in hypothalamic nuclei. Critical distinction.
ADH = vasopressin: promotes water reabsorption via aquaporin insertion in DCT/collecting duct. Deficiency = diabetes insipidus (polyuria, dilute urine, normal glucose).
Oxytocin: uterine contractions during labour (positive feedback); milk ejection reflex.
Thyroid hormones T3 and T4 require iodine. T4 is a prohormone; T3 is 3–5× more active.
Calcitonin: from thyroid C-cells; lowers blood calcium. PTH: from parathyroid glands; raises blood calcium. They are antagonists.
Adrenal cortex zones (GFR = Salt-Sugar-Sex): Glomerulosa = aldosterone (Salt); Fasciculata = cortisol (Sugar); Reticularis = androgens (Sex).
Adrenal medulla: adrenaline + noradrenaline (catecholamines); fight-or-flight; modified sympathetic ganglion; neural crest origin.
Pancreatic islets: α-cells = glucagon (hyperglycaemic); β-cells = insulin (hypoglycaemic); δ-cells = somatostatin (inhibits both).
Insulin is the only hypoglycaemic hormone. Glucagon, cortisol, adrenaline, and GH are all hyperglycaemic counter-regulatory hormones.
Gigantism = GH excess before growth plate fusion (child). Acromegaly = GH excess after fusion (adult, no height increase).
Cretinism = childhood hypothyroidism (stunted growth + irreversible mental retardation). Myxoedema = adult hypothyroidism (puffy face, low BMR, reversible).
Graves' disease = autoimmune hyperthyroidism; TSI mimics TSH; pathognomonic sign = exophthalmos.
Addison's disease = adrenal cortex hyposecretion; characteristic hyperpigmentation (excess ACTH has MSH-like activity → melanin).
Cushing's syndrome = cortisol excess; moon face, buffalo hump, hyperglycaemia.
Type 1 DM = autoimmune β-cell destruction (insulin-dependent). Type 2 DM = insulin resistance.
Peptide hormones = water-soluble → surface receptors → cAMP. Steroid hormones = lipid-soluble → intracellular receptors → gene transcription.
Negative feedback is the universal regulatory mechanism: end-hormone inhibits hypothalamic and pituitary driving signals.
Prolactin is unique: primarily under inhibitory control $\frac{dopamine}{PIF from hypothalamus}$ .
Thymus produces thymosins → T-lymphocyte maturation. Involutes with age.
Pineal gland → melatonin (increases in darkness) → regulates circadian rhythm.
Testosterone: from Leydig cells (LH-stimulated). FSH → Sertoli cells → spermatogenesis.
Aldosterone (RAAS-regulated) → Na+ retention + K+ excretion in DCT → increases blood volume and pressure.