Anatomy of the Urinary System

How do the kidneys and urinary system work?

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

Illustration of the anatomy of the urinary system, front view

The kidney and urinary systems help the body to eliminate liquid waste called urea, and to keep chemicals, such as potassium and sodium, and water in balance. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys, where it is removed along with water and other wastes in the form of urine.

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Other important functions of the kidneys include blood pressure regulation and the production of erythropoietin, which controls red blood cell production in the bone marrow. Kidneys also regulate the acid-base balance and conserve fluids.

Illustration of the anatomy of the kidney

Kidney and urinary system parts and their functions

  • Two kidneys. This pair of purplish-brown organs is 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. These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, 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. This triangle-shaped, hollow organ is 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, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.
  • Two sphincter muscles. These circular muscles 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. This tube 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. When all the signals occur in the correct order, normal urination occurs.
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Facts about urine

  • Adults pass about a quart and a half of urine each day, depending on the fluids and foods consumed.
  • The volume of urine formed 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.
8 Signs and Symptoms of Kidney Stones What are kidney stones? Kidney stones are hard collections of salt and minerals often made up of calcium or uric acid. They form inside the kidney and can travel to other parts of the urinary tract. Stones vary in size. Some are as small as the period at the end of this sentence — a fraction of an inch. Others can grow to a few inches across. Some kidney stones can become so large they take up the entire kidney. A kidney stone forms when too much of certain minerals in your body accumulate in your urine. When you aren’t well hydrated, your urine becomes more concentrated with higher levels of certain minerals. When mineral levels are higher, it’s more likely that a kidney stone will form. About 1 out of every 11 people in the United States will get a kidney stone. Stones are more common in men, people who are obese, and those who have diabetes Smaller kidney stones that remain in the kidney often don’t cause any symptoms. You might not notice anything is amiss until the ...
Urinary system anatomy and physiology review The urinary system is responsible for the production and elimination of urine when a type of waste called urea is removed from the blood. Urea is produced when protein-containing foods are broken down in the body. Urea is carried in the bloodstream to the two kidneys, where urine is formed. The two ureters, the urinary bladder, and the urethra, are responsible for the elimination of urine. Figure illustrates the urinary system in relationship to the body, and Figure illustrates the interior and exterior features of the urinary system organs. FIGURE. The urinary system FIGURE. (A) Frontal section of the right kidney showing internal structures and blood vessels. (B) Magnified section of the kidney shows several nephrons. (From Scanlon, VC, and Sanders, T: Essentials of Anatomy and Physiology, ed 5. FA Davis, Philadelphia, 2007, p 422, with permission.) The kidneys, each about the size of a fist, help to regulate the water, electrolyte (ionized salt), and acid-base content of th...
Polycystic Kidney disease ICD-9: 753.12 Description Polycystic kidney disease is a developmental defect of the collecting tubules in the cortex of the kidneys. Groups of tubules that fail to empty properly into the renal pelvis slowly swell into multiple, grapelike, fluid-filled sacs or cysts. The pressure from the expanding cysts slowly destroys adjacent normal tissue, progressively impairing kidney function. Both kidneys are usually affected and are grossly enlarged. Polycystic kidney disease is one of the most common hereditary diseases in the United States, affecting more than 600,000 people. It is the cause of nearly 10% of end-stage renal disease and affects men, women, and all races equally. Etiology There are two forms of the disease, each due to a genetic defect. The more common adult form, usually manifested during midlife, is an autosomal dominant defect. The much less common infant and childhood forms, manifested at birth or during childhood, are autosomal recessive defects. The followin...
Acute Tubular Necrosis ICD-9: 584.5 Description Acute tubular necrosis is the rapid destruction or degeneration of the tubular segments of nephrons in the kidneys. The disease is characterized by a sudden deterioration in renal function, with resulting accumulation of nitrogenous wastes in the body. Impaired or interrupted renal function from acute tubular necrosis is considered reversible. Etiology The majority of cases of acute tubular necrosis are due to renal ischemia, or the interruption or impairment of blood flow in and out of the kidneys. This disease is the most common cause of acute renal failure in critically ill persons. Although there can be numerous causes for such impairment, renal ischemia leading to acute tubular necrosis is most frequently produced by severe bodily trauma or as a complication following surgery. The renal tubules also can be damaged in other ways. Acute tubular necrosis may be toxin induced (as a result of exposure to solvents, heavy metals, or certain medication...
Pyelonephritis (Acute) ICD-9: 590.10 Description Pyelonephritis, also called infective tubulointerstitial nephritis or kidney infection, is inflammation of the kidney and renal pelvis due to infection. One or both kidneys may be affected. The infection can result in the destruction or scarring of renal tissue, impairing kidney function. It is the most common type of kidney disease and is more common in women than in men due in part to the anatomic difference between men and women. Etiology Pyelonephritis is most commonly due to infection by the bacteria Escherichia coli. E. coli is a normal intestinal bacteria that grows rapidly. It is found in fecal matter. Proteus, Pseudomonas, Staphylococcus, and Enterococcus bacteria are less frequent agents of the infection. The bacteria typically ascend to the kidneys from the lower urinary tract, but they also may enter the kidneys through the blood or lymph. Women, particularly those who are pregnant or who practice poor genital hygiene, are at risk. In m...