excretes

Excretion is the biological process by which organisms remove metabolic wastes and toxic substances from their bodies. The term excretes can refer to the wastes produced or to the act of eliminating them.

Excretion differs from secretion, which releases substances for use by the organism or for signaling. Excretory products are wastes that the body no longer needs and wishes to dispose of.

Common waste materials include nitrogenous wastes such as ammonia, urea, and uric acid, as well as carbon dioxide and water produced by metabolism. Other soluble toxins, drugs, and bile pigments may also be eliminated.

The excretory system relies on several organs and pathways. Kidneys filter blood to form urine, guided by the nephrons that balance water, salts, and wastes. The liver converts ammonia to urea for safer transport. The lungs expel carbon dioxide, and the skin releases salts and water as sweat. The digestive tract eliminates unabsorbed material and certain metabolites.

Animal excretion strategies vary with water availability. Ammonotelic species release ammonia directly (many aquatic organisms); ureotelic species convert ammonia to urea (mammals, most amphibians); uricotelic species excrete uric acid (birds, reptiles), a strategy that conserves water.

In plants, excretion is less centralized. Plants may release volatile compounds, exude resins or waste sap, or lose water and gases through stomata. Some processes, like guttation, involve the release of liquid water under high soil moisture.

Understanding excretion is important for health and ecology. Kidney dysfunction, dehydration, or electrolyte imbalances can impair excretion, leading to toxin buildup. Excretory processes are tightly linked to osmoregulation and homeostasis.