Ultra-Concise 5-Bullet Revision

Excretion modes: Ammonotelism (aquatic → ammonia), Ureotelism (terrestrial → urea via liver ornithine cycle), Uricotelism (birds/reptiles → uric acid as semi-solid paste). Toxicity: Ammonia > Urea > Uric acid. NEET traps: tadpoles = ammonotelic; adult frogs = ureotelic; marine fish = ureotelic.
GFR + Urine: GFR = 125 mL/min → 180 L filtrate/day → 99% reabsorbed by tubules → only ~1.5 L urine/day. Never confuse filtrate volume (180 L) with urine volume (1.5 L).
Loop permeability: Descending limb = water-permeable, solute-impermeable (fluid concentrates). Ascending limb = NaCl-permeable, water-impermeable (fluid dilutes, builds 300–1200 mOsm/L medullary gradient). Use mnemonic: D = Drinks water, A = Allows salts out.
Hormones: ADH $\frac{hypothalamus}{posterior pituitary}$ → water reabsorption in DCT + collecting duct. Aldosterone (adrenal cortex) → Na+ in, K+ out, in DCT (RAAS effector: Low BP → Renin → Ang I → ACE → Ang II → Aldosterone). ANF (cardiac atria, high volume) → Na+ excretion (opposes aldosterone).
Disorders + Dialysis: Uremia = urea in blood; renal calculi = calcium oxalate most common; glomerulonephritis = inflamed glomeruli (proteinuria + haematuria). Haemodialysis = semipermeable membrane, dialysing fluid with normal glucose + amino acids, zero urea, to selectively remove waste.