13.1 Excretion in humans

How the human body removes metabolic waste — CO₂ excreted via the lungs, urea + excess water + ions excreted via the kidneys (with the four-organ urinary system: kidneys → ureters → bladder → urethra). HL extends to the kidney's internal anatomy (cortex + medulla) and the nephron's two-stage operation (filtration at the glomerulus, reabsorption of all glucose, most water, and some ions in the tubule), plus the liver's role in assimilating amino acids into proteins and deaminating excess amino acids to form toxic urea.