Explanation

Excretion removes metabolic wastes. Kidneys: filter blood, remove urea, regulate water and salt balance, produce urine. Nephrons are functional units.

Liver: produces urea (from protein breakdown), detoxifies substances, produces bile. Lungs: excrete CO₂ and water vapor. Skin: excretes some water, salts through sweat.

Kidney disease requires dialysis (artificial filtering) or transplant. Maintaining excretory health: drink enough water, avoid excess salt and protein, limit alcohol.