Excretion is the process by which organisms remove toxic materials and substances that are in excess of their requirements from the body. This includes waste products from chemical reactions, excess water and salts from the diet, and spent hormones.

Many chemical reactions within cells produce poisonous byproducts that must be eliminated. A key example is carbon dioxide, a product of glucose breakdown during respiration, which is removed by the lungs.

Excess amino acids are deaminated in the liver, a process that converts them into glycogen and urea. Urea is then transported by the blood to the kidneys for expulsion.

Urea and uric acid, which are derived from the breakdown of proteins, contain nitrogen. Due to their nitrogen content, these substances are commonly referred to as nitrogenous waste products.

The body takes in more water and salts through food than it needs. These excess substances must be removed efficiently to prevent harmful buildup.

Hormones, which regulate various bodily functions, are modified in the liver after they have served their purpose. They are then excreted by the kidneys.

The liver plays a crucial role by breaking down excess amino acids to produce urea. It also excretes bilirubin, a breakdown product of hemoglobin, with bile into the small intestine, which contributes to the color of feces.

While primarily responsible for oxygen intake, the lungs also function as excretory organs by removing carbon dioxide from the body. They also release water vapor, though this is an unavoidable loss rather than a controlled excretory function.

The kidneys are vital excretory organs that filter urea and other nitrogenous wastes from the blood. They also excrete excess water, salts, hormones, and drugs, forming urine.

Sweat, composed of water, sodium chloride, and traces of urea, is expelled through the skin. While this process removes substances from the body, sweating is primarily a thermoregulatory response and not considered a primary excretory function in the same way as the kidneys or lungs.