Excrete

Excrete is the process by which living organisms discharge waste products produced by metabolism and other cellular activities. Excretion is essential for homeostasis, preventing the buildup of toxic substances, regulating fluid and electrolyte balance, and maintaining acid-base status. It is distinct from secretion, which is the production and release of substances primarily for use elsewhere in the organism.

Most animals produce nitrogenous wastes (ammonia, urea, or uric acid) in varying forms and excrete them through urine, feces, sweat, or expired air, depending on evolutionary adaptations and habitat. For example, aquatic species may excrete ammonia directly into water, while mammals typically convert ammonia to urea, and birds and reptiles convert it to uric acid to conserve water.

Key excretory organs include the kidneys, which filter blood to form urine through filtration, reabsorption, and secretion; the liver, which detoxifies harmful substances and modifies waste; the lungs, which exhale carbon dioxide and water vapor; and the skin, which releases sweat. The digestive tract also eliminates indigestible material as feces.

In humans and many other animals, excretion coordinates with circulatory and endocrine systems to regulate blood volume, pressure, pH, and electrolyte balance, supporting overall metabolic stability. While plants excrete waste less visibly, they manage waste through storage, detoxification, and occasional loss via guttation or surface exudates.