The Excretory System

The body produces waste when it converts food into energy, fights diseases and repairs damaged cells. Body wastes are toxic or poisonous so they have to be removed from the body. The removal of waste from the body is called excretion. The body’s main organs of excretion are the kidneys. What if the kidneys fail to function?

The kidneys are the body’s main excretory organs. When they fail to function, a persons’ life becomes endangered because waste can poison the body. An artificial kidney is a machine that filters blood by a process called dialysis. A tube inserted into the artery in the patients arm carries blood to the machine where it is pumped through permeable tubes in a container of liquid. Waste in the blood pass through the walls of the tubes into the liquid while the substances that the body needs pass from the liquid into the blood. The clean blood is returned to the patient’s body through a tube connected to a vein in his or her leg. The blood must pass through the machine twenty times before it is cleaned properly. Dialysis is not only painful, it is also expensive.

The kidneys are a part of the urinary system which, together with the lungs, skin and some other body organs, makes up the excretory system.

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Parts of the urinary system and their functions. The urinary system consists of two kidneys, two ureters, the urinary bladder and urethra. The kidneys are the main organs of the urinary system. The ureters, bladders and urethra form a passage way for the release of liquid waste. The kidneys are bean-shaped organs located at the back of the abdominal cavity. The right kidney lies below the liver while the left kidney lies below the spleen. The right kidney is slightly lower than the left kidney because the liver takes up much of the space on that side. Each kidney is held in place by a fatty tissue which also cushions it.

Inside each kidney are millions of tiny filtering structures called nephrons, which are the structural and functional units of the kidney. Each nephrons has a cup-shaped capsule, called Bowman’s capsule, and a tube called renal tubule. At the top of each nephron is a bundle of tiny blood vessel called glomerulus. The capsule and the flomerulus form the structure which filters blood. The kidneys filter blood by removing water and nitrogenous waste to form urine and regulate the body chemistry. Each kidney has a drainage tube called the ureter. The wall of the ureter has a thick layer of smooth muscle which contracts rhythmically. The ureters are attached to the back of the bladder. The rhythmic contractions of the muscles in the ureter move urine to the bladder.

The urinary bladder is a muscular sac that stores urine before it is passed out of the body. The lining of the bladder can be stretched to enable it to store urine. Contractions of the bladder muscles expel the urine. At the base of the bladder is a tube which is about as wide as a pencil. This is the urethra, which carries urine outside the body. Sometimes you feel like urinating but, because a restroom is not in sight, you try to control it. Why can you do this? The urethra has a ring of skeletal muscle called the sphinater muscle around its opening. This muscle is like a valve that regulated the outflow of urine.

How the urinary system removes body wastes. Blood is the transport system of the body. It brings oxygen and nutrients to all the body cells. It also takes waste away from the cells to be excreted from the body. Each day about 180 liters of liquid from blood passes though your kidneys. However, not all of this fluid becomes urine. As blood passes through the kidneys, the millions of nephrons filter it. The filtered blood carrying most of this fluid and useful substances leaves the kidneys through the renal veins which take it to the heart to be pumped throughout the body. Filtered water and nitrogenous waste (called filtrates) go to the center of the kidney through the collecting ducts to form urine. Urine is mostly waste water, salts, salts and urea. From the kidney, urine passes through the ureter and is temporarily stored in the bladder. It leaves the body through the urethra.