Kidneys and Urinary Tract: Anatomy

Learn more about the structure, location and function of the kidneys and urinary tract

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The urine travels from the kidneys through the ureters into the bladder

© W & B / Jörg Kühn

What are the kidneys

The kidneys are excretory organs. The shape of a kidney is reminiscent of a bean. Put simply, the kidneys filter substances out of the blood that are superfluous or do not belong there. These are then excreted in the urine. For example, the kidneys help to keep the pH value in the body within its narrow limits or to control the salt-water balance. In addition, the kidneys also produce hormones that are involved, for example, in blood formation or in regulating blood pressure.

Where are the kidneys?

There are two kidneys, a left and a right. They are located in the area of ​​the flanks, which is why the pain is often localized there in kidney disease. The right kidney is usually a little lower than the left because the liver is located above the right kidney and takes up a lot of space.

Video: location of the kidneys in the body

Which hormones are made in the kidney?

The kidneys make various hormones:

  • Erythropoietin: This hormone stimulates the production of red blood cells. It is released when the oxygen supply to the kidney cortex is insufficient.
  • Renin: Is involved in the regulation of the salt-water balance and blood pressure. It is released, for example, when the blood pressure in the blood vessel supplying the kidneys is not high enough.
  • Calcitriol (vitamin D3): In the kidneys, vitamin D produced in the body is converted into its active form in a final production step. Before that, there are production steps that take place in the skin and liver.

Kidney and glomeruli

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Structure of the kidney

The kidney consists of the renal cortex, the renal medulla and the renal pelvis. The so-called kidney corpuscles are located in the kidney cortex. This is where part of the kidney's filtering work takes place: A wide variety of substances and a large amount of fluid first leave the blood vessels in small clusters of vessels, the so-called glomeruli, and enter the tubules as so-called primary urine, as the small urinary tracts are called. These tubules open into the loop of Henle in the renal medulla. The urine is fine-tuned in the tubules and loop of Henle: A large part of the fluid initially filtered out of the blood vessels and other substances such as potassium and sodium are removed from the primary urine and absorbed into the body as required by the body, while other substances are in turn are added until the urine is finished and reaches the renal pelvis via the collecting tubes and calyxes.

Lower urinary tract in women

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Upper urinary tract

The urine formed in the kidneys passes through the ureters (ureters) into the bladder, where it collects. The kidneys and ureters together are sometimes called the upper urinary tract.

Lower urinary tract

The urethra leads out of the bladder and, for anatomical reasons, is much shorter in women than in men. This is one of the factors that make women more likely to suffer from urinary tract inflammation. Because germs can more easily get into the bladder via the short urethra and trigger a cystitis there. The bladder and urethra are also considered the lower urinary tract.

Lower urinary tract in men

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With kidney disease, the function of the kidneys can be disturbed. Fluid and waste materials are then no longer excreted as well. At first, those affected often do not notice it for a long time. Later on, symptoms such as water retention in the legs may appear. If the kidney can no longer adequately fulfill its function in the long term, all that remains is blood washing (dialysis) or a kidney transplant.

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