Purpose of the Excretory System

As human cells metabolize and create energy, waste is excreted in the form of water and carbon dioxide. These two byproducts are the end results in the breakdown of essential foods, such as carbohydrates, fats and proteins. Chemicals, such as nitrogen, sulfur and phosphorous are stripped from the beneficial compounds of food groups and excreted into extracellular fluid. The excretory system filters these byproducts out of the blood and removes them from the body.

Structure

• The human excretory system is comprised of the kidneys, bladder, ureters and the urethra. The functional unit of the kidneys is the nephron, which is where filtration begins. Once beneficial products are restored to the body and waste is removed, the urea is sent down the ureters where it is held in the bladder. The bladder is an expandable, muscular organ that holds urea until it is voluntarily released through the urethra.

Nitrogen Removal

• Nitrogenous waste is a byproduct of proteins. Proteins are made as long chains of amino acid groups. Cells remove the nitrogen atoms from proteins before its conversion into a useful energy product. The removed nitrogen atoms combine with hydrogen to form ammonia. Ammonia is toxic to the body, so it's the function of the excretory system to remove the compound through the kidneys. The kidneys convert ammonia to urea, which is sent to the bladder until it is excreted.

Balance of Salt and Water

• The kidneys function as a filter that regulates the amount of water loss and ion consumption. Humans have a pair of kidneys, but most people can function with only one, taking care to eat properly and avoiding drugs and alcohol. Inside the kidney are thousands of glomeruli that receive blood from all other tissues. The salt concentration within the nephron allows kidneys to absorb water and ions that are beneficial to the body and sends them back to the blood stream. Waste products are converted to urea and sent down the ureter to the bladder.

The Nephron

• The nephron is the main, functional unit of the excretory system. The nephron consists of glomerulus and a Loop of Henle. The Loop of Henle is a U-shaped vessel that has increased sodium levels and water. As waste products move down the tube, they remain in the loop to be excreted while beneficial nutrients are absorbed in the tissue. At the top, sodium concentration is low, so ions are able to permeate through the tube's membrane. Conversely, as sodium becomes denser, water is forced into the kidney tissue through osmotic pressure. These absorbed ions and water molecules are recycled in the body for future use.

Disease

• Diseases of the excretory system are usually painful, and can be deadly if left untreated. Nephritis and nephrosis are two diseases in which the nephrons become inflamed. If nephrons die, the kidney is unable to remove waste and chronic renal failure occurs. Urinary tract infections occur when bacteria are able to infect the urethra, bladder, ureter and sometimes the kidneys. Urinary tract infections are eliminated through the use of antibiotics.