The kidneys - anatomy, functions and common diseases

Leading Medicine Guide Editors
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Leading Medicine Guide Editors

Everyone has two kidneys, which cleanse the blood of harmful substances and produce urine. The kidney is a paired organ that is part of the urinary system. It can be described as the body's "sewage treatment plant", as the kidneys form urine and filter it out of the blood together with toxic substances that are no longer needed. All of a person's blood flows through the kidneys around three hundred times a day. This means that they filter an average of 1500 liters a day.

Article overview

Anatomy of the kidney

The kidney is one of the internal organs and is present in two parts. They are reddish-brown in color and shaped like a bean.

A single kidney has a transverse diameter of 5 to 6 centimeters, while the longitudinal diameter is 10 to 12 centimeters. The organ reaches a thickness of approx. 4 centimeters and weighs between 120 and 200 grams. Normally, the right kidney is slightly smaller than the left.

Anatomie der Niere

The renal portal is located on the inner edge of the kidney, through which the renal vein and the renal artery run. Blood containing waste products enters the kidney through the artery. The purified blood is transported out again via the vein. There are also several openings for nerves and lymph vessels at the renal portal.

The kidney is made up of three zones:

  • Renal pelvis: This is where the urine formed collects and drains downwards towards the bladder via the ureter
  • Renal medulla (medulla renalis)
  • Renal cortex (cortex renalis)

The medulla and cortex form the actual organ mass. They contain approx. 1 to 1.4 million small filter units, so-called nephrons, which filter harmful substances from the blood and form urine.

Other cells produce the hormones erythropoietin and renin. While erythropoietin produces red blood cells, renin regulates blood pressure.

Where are the kidneys located in the body?

The kidneys are located behind the peritoneum in the retroperitoneal space, which is outside the abdominal cavity. The peritoneum does not surround the organs.

Lage der Nieren
Position of the kidneys (the color does not correspond to reality)

As the liver is also located in the right upper abdomen, the right kidney is usually about two centimeters lower than the left kidney. In addition to the liver, the duodenum and the right colon bend are located in the vicinity of the right kidney. Neighbors of the left kidney are the stomach, spleen, parts of the pancreas and the descending area of the large intestine.

What functions do the kidneys have?

The kidneys act as filter organs. The entire volume of human blood flows through the kidneys around 300 times a day. From this, the kidneys first filter out the primary urine, i.e. unconcentrated urine. This contains components such as waste products and toxic substances. These harmful substances must be excreted from the body. The kidneys filter them out of the primary urine and produce the final urine - around 1.5 liters for each person every day.

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On the other hand, the kidneys return substances that are still needed by the body to the bloodstream. These are mainly sugar and water.

The urine is collected in the renal pelvis. From there, it is transported out of the body via the ureter and bladder.

Harnwege
The urinary tract © Sebastian Kaulitzki / Fotolia

The kidneys also play an important role in the body's water balance and in regulating blood pressure. Furthermore, the organs also support the electrolyte balance by controlling the urine concentration. The kidneys also produce hormones that are important for the formation of blood and vitamin D3.

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Common kidney diseases

Various diseases can occur in the kidneys. These include

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Some diseases mean that the kidneys can no longer perform their important tasks. Toxic substances accumulate in the body due to inadequate disposal. In order to prevent life-threatening poisoning of the organism, another form of blood purification is required, which is usually done by dialysis.

 

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Risk factors

Some risk factors favor the development of kidney diseases (nephropathies). For example, chronic kidney failure is often caused by other chronic diseases. These are primarilydiabetes mellitus. Because the sugar in the blood is too high in the long term, the kidneys are affected to such an extent that they are no longer able to perform their cleansing function. Diabetics therefore need to have their sugar levels optimally adjusted to prevent kidney damage.

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Symptoms

As a rule, symptoms of kidney disease begin gradually. This leads to

  • reddish discoloration of the urine
  • an unpleasant urine odor
  • kidney pain
  • dull back pain
  • colicky pain in the back that radiates to the bladder
  • edema of the ankles or eyelids
  • nocturnal urge to urinate
  • foaming urine
  • low urine output

If the kidney disease progresses further, this leads to general symptoms such as

  • a feeling of weakness
  • nausea
  • vomiting
  • loss of appetite
  • itching
  • Water retention in the legs
  • paleness
  • a sour body odor

Diagnosis of kidney disease

The most important diagnostic method is the microscopic examination of a urine sample, which is checked for the presence of certain substances such as sugar, protein or uric acid. Further examination methods include

Conclusion on the kidney

Because the kidneys are one of the most important human organs, prevention is extremely important. To counteract risk factors such as high blood pressure and diabetes, it is recommended to lower blood pressure and blood sugar levels.

The better the control of blood pressure and blood sugar, the more the risk of kidney disease is reduced. A healthy diet and abstaining from tobacco also contribute to this.

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