If you knew there were thieves hidden in your house, what would you do? You would surely do everything possible to find them and throw them out of your house before they do some harm to you. This is exactly what our excretory system does. Hidden throughout your body are dangerous poisons that must be removed in order for it to survive. The process of excretion involves finding and removing waste materials produced by the body. During circulation, Blood passes through the kidneys in order to deposit used and unwanted water, minerals, and a nitrogen-rich molecule called urea. The kidneys filter the wastes from the Blood, forming liquid called urine. All of it needs to be removed from your system. This occurs through urination. The kidneys funnel the urine into the bladder through tubes called Ureters. The bladder stores the urine until Muscular contractions force the urine out of the body through the Urethra. If your kidneys are diseased and not working properly, the build-up of waste in your system will cause great harm to your body. Hence what we are dealing here, are the organs in the body that have a role in removing metabolic wastes. Metabolic wastes are by-products of metabolism. There are four organs that are a part of the excretory system. They are: LUNGS- As respiration occurs carbon dioxide is produced as a waste product. As the carbon dioxide accumulates in body cells, it eventually diffuses out of the cells & into the bloodstream, which eventually circulates to the Lungs. And here, in the Alveoli of the Lungs, carbon dioxide diffuses from the Blood, into the lung tissue, and then leaves the body every time we exhale. LIVER- Some proteins & other nitrogenous compounds are broken down in the Liver by a process called deamination. As a result of these reactions, a nitrogenous waste called urea is formed. SKIN- Skin also helps to remove metabolic wastes through sweat. Sweat comes out of pores in your Skin. Sweat is a mixture of three metabolic wastes: water, salts, & urea. URINARY SYSTEM- Three of the four major metabolic wastes produced by the body are filtered from the Blood by the kidneys. They are water, salts, & urea (the 4th, carbon dioxide, is excreted by the Lungs). And the system that takes care of removing these wastes from our body is called excretory system. So in this section, we will get familiar with the excretory system of our body.

The word excretion means the removal of waste substances from the body. Several organs are involved with the excretory system, including the kidneys, sweat glands, Lungs and rectum, The primary organs of excretions, however, are the Kidney. Excretion is vital to the health of the body because the wastes are poisonous. If the wastes build up and are not eliminated, they can cause serious problems. Let us know the different organs, which make up our excretory system.

KIDNEY The kidneys are bean-shaped organs, each about 4 to 5 inches long. If you have ever seen a Kidney bean, then you will have a pretty good idea what the kidneys look like. They lie on either side of the spinal column, just behind the space that contains the Digestive organs (abdominal cavity). If the Kidney is cut into two halves, the inner section is called the renal medulla and the outer section is called the renal cortex. Renal cortex is where the main function of the kidneys happens. Each Kidney (which can be thought of as big filters) is made up of thousands of tiny filtering sub-units called nephrons. URETER From the kidneys, urine travels down two thin tubes called Ureters to the bladder. The Ureters are about 8 to 10 inches long. Muscles in the ureter walls constantly tighten and relax to force urine downward away from the kidneys. If urine is allowed to stand still, or back up, a Kidney infection can develop. Small amounts of urine are emptied into the bladder from the Ureters about every 10 to 15 seconds. URINARY BLADDER The bladder is an expandable, Muscular sack. It is a hollow organ shaped like a balloon. Urine accumulates in the bladder as it arrives from the Ureters. It sits in your pelvis and is held in place by ligaments attached to other organs and the Pelvic Bones. The bladder stores urine until you are ready to go to the bathroom to empty it. It swells into a round shape when it is full and gets smaller when empty. If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours. URETHRA The Urethra is a tube that drains urine from the bladder out of the body. In males, the Urethra is about 8 inches long, ends at the tip of the Penis. In females, the Urethra is about 1½ inch long, ending at the vulva. In females, the Urethra is a tube that conveys urine from the urinary bladder to the outside of the body. Whereas in males, the Urethra functions as a urinary canal as well as a passageway for cells and secretions from the reproductive organs.

The principal function of the urinary system is to maintain the volume and composition of body fluids within normal limits. One aspect of this function is to rid the body of waste products that accumulate as a result of cellular metabolism, and because of this, it is referred to as the excretory system.

Your body takes nutrients from food and uses them to maintain all bodily functions including energy and self-repair. After your body has taken what it needs from the food, waste products are left behind in the Blood and in the bowel. The urinary system works with the Lungs, Skin, and intestines, all of which also excrete wastes to keep the chemicals and water in your body balanced. Adults eliminate about a quart and a half of urine each day. The amount depends on many factors, especially the amounts of fluid and food a person consumes and how much fluid is lost through sweat and breathing. Certain types of medications can also affect the amount of urine eliminated. Each Kidney continuously produces urine, which then drains through the ureter into the bladder at a low pressure. It is in kidneys that materials such as urea, salts, water, glucose, & others pass from the Blood into the nephron. These materials (referred to as the "filtrate") pass through the tubule, also known as the loop of henle. As the filtrate travels through the tubule, useful substances are reabsorbed into the surrounding Capillaries (which connect to Veins that will transport the "clean" Blood back to the Heart via the Renal vein). About 180 litres of filtrate is produced each day, but only 1.5 liters of urine is formed. So as you can see, most materials that initially enter the nephron are reabsorbed, leaving only the urea, salts, & some water in the tubule. These metabolic wastes form urine is transported to the urinary bladder by the collecting tubule. From the bladder, urine drains through the Urethra and exits the body through the Penis in males and the vulva in females. Under normal circumstances, urine is free of bacteria and other infectious organisms. In brief, the functions of the excretory system are:

Filtration and excretion of waste products The urinary system maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine. Regulates the concentrations of various electrolytes in the body fluids and maintains normal ph of the Blood. Maintains fluid homeostasis in the body. The urinary system controls red Blood Cell production by secreting the hormone erythropoietin. Regulates Blood pressure. The urinary system also plays a role in maintaining normal Blood pressure by secreting the enzyme renin.

Enuresis Glomerulonephritis Renal Stone Acute Renal Failure Chronic Renal Failure Nephrosis Pyelonephritis Urethral Stricture Urethritis Urinary Retention Urinary Tract Infection