What Kidneys Do?


The kidneys are one of the most important organs of both our body and urinary system. Although single kidney is sufficient for continuing of life, life without the kidney functions is out of the question.

These two bean-shaped organs help the body to dispose of the wastes as urine.

For more information about the anatomy of the kidney, you can read:
Anatomy of the Kidney



At the same time, they send back the filtered blood to the heart and thus provide the circulation of blood which is free of waste in the body.

To give an overview of kidney functions in the body;

  • Preserving the overall fluid balance of body
  • Filtering and regulating minerals from blood
  • Filtering of wastes which the body gets from foods, drugs and toxic substances
  • Production of hormones that regulate the blood pressure, stimulate red blood cell production and bone growth

Importance of Kidneys

As everyone knows, the main kidney functions are the removal of waste products and elimination of excess fluid from the body. These waste products and excess fluid are excreted through the urine formed by the filtration of blood.
Urine formation is provided after successive highly complex reabsorption and excretion mechanisms.

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Balance of fluid and minerals

At the same time, the balance of important minerals such as potassium and sodium, which are extremely critical for the body, is maintained through kidney functions. So that people who have nonfunctional kidneys, to maintain their lives, provide the balance of these important minerals by dialysis. 
In addition, the acid-base balance, which is also extremely important for the body, is provided both by the kidney’s blood-filtering function and the hormones it produces.

Hormones secreted from body

Apart from functions such as filtering blood, removing waste products and excess fluid from the body and maintaining mineral and acid-base balance, the kidney also supports other organ’s vital functions with a number of hormones it produces.

With erythropoietin, which is one of the hormones that kidney produce, it stimulates the production of red blood cells. This is the reason why anemia is frequently seen in patients with dysfunctional kidneys and who goes into the dialysis.

Also with renin, another hormone kidney produces, it helps to regulate blood pressure.
Kidney also secretes calcitriol which is the active form of vitamin D and thrombopoietin. With calcitriol it increases the absorption of calcium and phosphate, with thrombopoietin it stimulates the megakaryocytes.

2. How do the Kidneys Work?

Each kidney consists of 1 million nephrons which are the filtration units.
Each nephron consists of a filter called a glomerulus and tubules which absorption and reabsorption functions are made.

Nephrons mainly function in two steps;

1-Glomerulus filters the blood
2-Tubules provide the reabsorption of necessary substances such as sodium or glucose into the blood and secretion of some wastes into the urine.

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a. Filtering function of glomerulus

As blood flows into the nephron, it enters the cluster of tiny capillaries. Under favour of the thin walls of the glomeruli, small molecules, waste materials and liquid can get into the tubule. Therefore, large molecules, such as proteins or blood cells, remain in the blood vessels.

b. Excretion and reabsorption functions of tubules

As the filtered liquid transports through the tubule, almost all of the water is reabsorbed back into vessel which is extending along the tubule.
When water is reabsorbed, minerals and nutrients that the body needs are also reabsorbed with water. Water and minerals which remain in the tubule form urine and are excreted outside the body.

c. Blood flow of kidney

Blood comes to the kidney through the renal artery. This large blood vessel divides into small branches until it reaches the capillary size of the nephrons. In the nephrons, blood is filtered through the thin capillary vessels of the glomeruli and then reaches the renal vein and leaves the kidney.
All the volume of blood circulating, passes through the kidney several times in one day. The kidney filters approximately 140 liters of blood and removes waste products and excess fluid in 24 hours.
Most of the fluids and nutrients filtered through the glomeruli are reabsorbed back into the blood from the tubules. Only about 1500 ml is excreted as urine.

3. Five Vital Functions of Kidney

The kidneys are constantly working to maintain the vital functions of the body and keep it healthy. There are 5 important functions performed by the kidneys in order to function properly.

a. Eliminates the excess fluid and waste products

The kidney acts as a filter and cleanses the remains from the body. This prevents the accumulation of waste materials and excess fluid in the body.

b. Regulation of blood pressure

If the blood pressure is low, the kidney secretes a variety of hormones in order to work properly, thus increasing the blood pressure. In case of, the blood pressure is high, it increases the fluid excretion into the urine and again secretes various hormones to lowering it.

c. Stimulation of the production of red blood cells

The kidney, sends signal to the bone marrow to produce more blood cells with its erythropoietin hormone. Thus, the number of red blood cells in the blood which provide your daily energy and carry oxygen to the whole body is increased.

d. Provide the health of bones

The kidneys produce calcitriol, which is the active form of vitamin D.

With the stimulation of vitamin D, calcium and phosphorus are absorbed in the gastrointestinal tract and strengthens the structure of the bones.

e. Regulation of acid base balance

The pH which occurs with balance of acid and base in the body is extremely important. All functions in the body can operate within a very narrow pH range. Therefore, the pH must be kept constant.
The kidney regulates the acid-base balance, which can vary due to some foods that you eat or destruction of blood cells.

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4. Kidney Conditions and Symptoms

The kidney is one of the most highly sensitive organ for various diseases and conditions, as it has the task of cleaning and filtering all waste and toxic substances in the body.
Some of these conditions can be listed as follows;

  • Kidney stones
  • Cysts of kidney
  • Polycystic kidney disease
  • Chronic kidney disease
  • Nephrotic syndrome
  • Acute nephritis
  • Failure of the kidney
  • Glomerulonephritis
  • Pyelonephritis
  • Urinary tract infections
  • Hydronephritis
  • Uremia
  • Acidosis
  • Azotemia
  • Caliectasis

At the same time, these problems can cause a series of symptoms. These symptoms can be listed as follows;

  • Increase or decrease in urine volume
  • Blood in urine
  • Foamy urination
  • Fatigue
  • Inability concentrate
  • Trouble in sleeping
  • Cramps in muscles
  • Foot or ankle swellings
  • Appetite reducing
  • Puffiness around the eyes
  • Drying or itching of the skin

For more information about the diseases of the kidney, you can read:
How Kidneys Work


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