Excretory system

The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. It plays a key role in keeping our bodies healthy by getting rid of waste. This system works to eliminate the waste products of metabolism, which are by-products created when our cells produce energy and other needed materials.

In humans and other amniotes like mammals, birds, and reptiles, most of these wastes leave the body as urine. We also get rid of some waste through breathing out air and, for mammals, through sweating. The main organs involved in this process are part of the urinary system.

Because all healthy organs produce waste, the whole body depends on the excretory system to work well. If this system stops working properly, it can lead to serious health problems, such as kidney failure. Understanding how our excretory system functions helps us appreciate how our bodies keep themselves balanced and healthy.

Systems

Main article: Urinary system

The urinary system helps remove waste from our bodies. The kidneys are two bean-shaped organs that filter blood, taking out wastes like urea, salts, and extra water to make urine. They use tiny filters called nephrons to separate what the body needs from what it doesn’t. The cleaned blood leaves through the renal vein, while urine travels through tubes called ureters to the urinary bladder, which stores it until we urinate.

Main article: Respiratory system

Our lungs also help remove waste. During breathing, they release gases like carbon dioxide from the blood, which is a normal part of life.

Main article: Gastrointestinal tract

The large intestine moves food through the body and pushes out solid waste. It also takes in any remaining water before waste leaves the body.

Main article: Biliary system

The liver helps clean the blood by breaking down harmful substances. It changes poisons like ammonia into less harmful materials, which the kidneys then remove as urine.

Main article: Integumentary system

Our skin can also act as an excretory organ. Sweat glands release sweat, which helps control body temperature and remove small amounts of waste. Sweat is mostly water and helps keep the body cool.

Substances

Main article: Bile
Main article: Urine
Main article: Faeces
Main article: Sweat
Main article: Breath

The excretory system helps get rid of waste from our bodies. Bile, made in the liver and stored in the gallbladder, helps break down fats in our food. Urine forms in the kidneys when blood is filtered, removing waste and extra water, and then leaves the body through the bladder. Other wastes leave our bodies as faeces, sweat, and breath.

Clinical significance

Kidney stones

Main article: Kidney stone disease

Kidney stones are hard bits that can form inside the kidneys. They are made from things like calcium and uric acid that don’t dissolve properly in urine. Sometimes these stones are small enough to pass out of the body with urine, but larger stones can get stuck and cause a lot of pain. Doctors can help break up big stones using special waves or tools.

Pyelonephritis

Main article: Pyelonephritis

Pyelonephritis is an infection in the kidneys that happens when bacteria get into the urinary system. This can make a person very sick with fever and pain. Doctors treat it with medicines called antibiotics to kill the bacteria. Most people get better with treatment, but sometimes the infection can cause problems in the kidneys if it happens again.