Excretion
Excretion

The process, by which waste product of metabolism from the system of an organism are eliminated from the body.

Organs of the Excretory System

Lungs – removal of excess carbon dioxide
Liver – produces urea and uric acid as a by-product of the breakdown of proteins
Skin – removal of excess water, salt, urea and uric acid
Urinary System – kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
Kidneys perform several homeostatic functions:

Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the extracellular fluid.
Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.
Functioning of the kidney

The kidney removes metabolic and liquid toxic wastes as well as excess water from the organism.

Parts of the kidney

                         



Renal Arteries – 2 renal arteries constantly transport blood to the kidneys.
Kidneys – 2 kidneys composed of millions of nephrons constantly filter about 170 to 200 litres of blood to produce about 1.5 to 2 litres of urine daily.
Renal Veins – 2 renal veins return useful nutrients back into the bloodstream.
Ureters – 2 ureters carry urine from the kidneys to the urinary bladder.
Urinary Bladder – The urinary bladder temporarily stores urine until it is released from the body.
Urethra – The urethra is the tube that carries urine from the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a circular muscle called a sphincter.
Within each kidney there are an estimated one million microscopic nephrons, where blood filtration takes place. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerulus. The blood that flows through the glomerulus is under great pressure. This causes water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remain in the blood. As the blood continues in the excretory system, it passes through the renal tubule. During this time, reabsorption occurs: glucose and chemicals such as potassium, sodium, hydrogen, magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.