Anatomy of the Kidneys and Urinary System

Anatomy of the Kidneys and Urinary System

How do the kidneys and urinary system work?

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The body takes nutrients from food and converts them into energy. After the body has taken the food that it needs, waste products are left behind in the bowel and in the blood.

The kidneys and urinary system keep the chemicals and water in balance by removing a type of waste, called urea, from the blood. Urea is produced when food containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

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Kidney and Urinary System Parts and Their Functions

• Two kidneys-a pair of purplish-brown organs located below the ribs toward the middle of the back. Their function is to remove liquid waste from the blood in the form of urine; keep a stable balance of salts and other substances in the blood; and produce erythropoietin, a hormone that aids the formation of red blood cells.

The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries — called a glomerulus — and a small tube — called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

• Two ureters–narrow tubes that carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax, which forces the urine downward and away from the kidneys. If urine backs up or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.
• Bladder-a triangle-shaped, hollow organ located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine. The walls contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to 2 cups of urine for 2 to 5 hours.
• Two sphincter muscles-circular muscles that help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.
• Nerves in the bladder– the nerves alert a person when it is time to urinate or empty the bladder.
• Urethra-the tube that allows urine to pass outside the body. The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax to let urine exit the bladder through the urethra. Normal urination occurs when all the signals happen in the correct order.

Facts About Urine

• Adults pass about 1½ quarts of urine each day, depending on the fluids and food consumed.
• The volume of urine created at night is about half that formed in the daytime.
• Normal urine is sterile. It contains fluids, salts, and waste products. But it is free of bacteria, viruses, and fungi.
• The tissues of the bladder are isolated from urine and toxic substances by a coating that discourages bacteria from attaching and growing on the bladder wall.