The kidneys are bean-shaped and are each about the size of a child's fist. They perform several functions that are essential to health, the most important of which is to filter blood and produce urine. Without the kidneys, waste products and other toxins (chemicals or poisons that have harmful effects on the body) would soon build up in the blood to fatal levels. The kidneys also help control blood pressure and the level of salts and other chemical substances in the blood, as well as secrete (give off) a hormone that controls the production of red blood cells.

The urinary tract is made up of the:

kidneys
ureters
bladder
urethra
These organs work together to produce, transport, store, and excrete (remove from the body) urine, the yellowish fluid that contains waste products removed from the blood. Urine contains the by-products of our body's metabolism, salts, toxins, and water.

When you are asked to give a urine sample during a doctor's visit, the results reveal how well your kidneys are working. For instance, blood, protein, or white blood cells in the urine may indicate injury, infection, or inflammation of the kidneys. Glucose (sugar) in the urine may be a sign of diabetes.

How Are the Kidneys and Urinary Tract Important for Living?
Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (also known as stool), and urine. These wastes are secreted from the body in different ways: sweat is released through pores (tiny holes) in the skin and then evaporates; water vapor and carbon dioxide are exhaled (breathed out) from the lungs; and undigested food materials are formed into feces in the intestines and excreted from the body as solid waste in bowel movements. Waste substances from the blood are filtered and eliminated in liquid urine by the kidneys and urinary system.

The kidneys and urinary system also regulate many important body functions. The kidneys monitor and maintain the balance of body water, ensuring that body tissues receive enough water to function properly and be healthy.

The kidneys help regulate the acid-base balance (pH) of the blood and body fluids, which is necessary for the body to function normally. And by regulating salt levels through production of an enzyme called renin (as well as other substances), the kidneys help regulate blood pressure.

The kidneys also secrete a hormone called erythropoietin (pronounced: eh-rith-row-po-uh-ten), which stimulates and controls the body's red blood cell production.

Although the kidneys work as a pair to perform many vital functions, people can live a normal, healthy life with just one kidney. Some people are born with just one kidney.

Basic Anatomy
The kidneys lie just under the rib cage in the back, one on each side. The right kidney is located below the liver, so it is a little lower than the left one. Each kidney is about 5 inches long, 3 inches wide, and 1 inch thick.
Each kidney has an outer layer called the cortex, which contains the filtering units. Its middle region, the medulla, has 10 to 15 fan-shaped structures called pyramids. These pyramids drain urine into cup-shaped tubes called calyxes (pronounced: kay-luh-seez). A layer of fat surrounds the kidneys to cushion and help hold them in place.

At the hilus, which is the place where the bean shape is dented, facing toward the center of the body, large blood vessels enter and leave the kidney. The renal artery sends fresh blood into the kidney to be filtered. Filtered blood leaves through the renal vein and flows back to the heart. This continuous rich blood supply gives the kidneys their dark red color.

Each kidney contains about 1 million tiny filtering units called nephrons (pronounced: neff-ronz), which filter the blood and produce urine as a waste product. Each of the nephrons contains a filter called the glomerulus (pronounced: gluh-mer-you-lus), which is a network of tiny blood vessels known as capillaries. The fluid filtered from the blood by the glomerulus then travels down a tube called the tubule that adjusts the level of salts, water, and wastes that are excreted in the urine.

The renal pelvis, located near the hilus, collects urine in its chamber. From the pelvis, urine goes down a tube called the ureter (pronounced: your-eh-ter). The ureter carries the urine to the urinary bladder, a muscular collection sac in the lower abdomen. The bladder can hold about a half liter (2 cups) of urine at any given time. The urine is expelled from the bladder and out of the body through the urethra (pronounced: you-ree-thruh), a tube-like structure.

Short Answer
Tell the urinary function of each organ.

1. Kidney:

2. Ureter:

3. Bladder:

4. Urethra: