Excretory System

Several kinds of wastes, including sweat, carbon dioxide gas, feces (stool), and urine are produced by our body. These wastes exit the body by

  • Sweat is released through pores in the skin.
  • Water vapor and carbon dioxide are exhaled from the lungs.
  • Undigested food materials are formed into feces in the intestines and excreted from the body as solid waste in bowel movements.

In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra.


The kidneys are located just under the ribcage in the back, one on each side. The right kidney is located below the liver, so it’s a little lower than the left one.

The functional unit of Kidney is a Nephron. Each Kidney has around 1 million Nephrons that work as tiny filtering units which remove the harmful substances from the blood. Each of the nephrons contains a filter called the glomerulus, which contains a network of tiny blood vessels known as capillaries. Blood travels to each kidney through the renal artery. Once in Nephrons, it is filtered by glomerulus then travels down a tiny tube-like structure called a tubule, which adjusts the level of salts, water, and wastes that are excreted in the urine. Filtered blood leaves the kidney through the renal vein and flows back to the heart. The continuous blood supply entering and leaving the kidneys gives the kidneys their dark red color.


Urine is a concentrated solution of waste material containing water, urea (a waste product that forms when proteins are broken down), salts, amino acids, by-products of bile from the liver, ammonia, and any substances that cannot be reabsorbed into the blood.  Urine also contains urochrome, a pigmented blood product that gives urine its yellowish color.

Antidiuretic hormone

Antidiuretic hormone (ADH) from the pituitary promotes water retention by the kidneys, and its secretion is regulated by a negative feedback loop involving blood water and salt balances.

Other functions of Kidney

The kidneys also secrete the hormone erythropoietin, which stimulates and controls red blood cell production. In addition, the kidneys help regulate the acid-base balance (or the pH) of the blood and body fluids.