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How much blood is there in the body?

Written by: Editors

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We cannot live without blood, as this red liquid fulfils a number of very important functions in our body. This article will deal with the composition of blood and what you need it for. In addition, we answer the question of how many litres of blood a human being has in their body.

What is blood made up of?

Blood roughly consists of four components:

  • Red blood cells;
  • White blood cells;
  • Platelets;
  • Plasma.

About 40% of blood consists of red blood cells, and there are around 25 thousand billion of them in the human body. Red blood cells look like round discs and as the name implies, these are the cells that give blood its red colour. White blood cells are present in much smaller numbers, with around 35 billion of them in the human body. These are the “soldiers”, protecting us against pathogens. There are also between 800 and 2500 billion platelets in the body.

About half (45%) of our blood consists of red and white blood cells and platelets. The other half (55%) is made up of plasma, of which 90% is water. The blood cells and platelets are located in the plasma, whose main function is to transport blood cells, nutrients and other substances such as proteins, vitamins and hormones.

The function of blood

Transport oxygen

Blood fulfils a number of roles crucial to our existence. The main function of blood is the transport of oxygen from the lungs to the rest of the body. Red blood cells in the lungs bind the inhaled oxygen to itself and take it elsewhere in the body. The cells in our bodies convert oxygen into carbon dioxide, which the red blood cells bring back to the lungs, which is then exhaled. Because our heart pumps blood continuously through the body, there is a continuous input and output of oxygen and carbon dioxide.

Transport of nutrients

In addition to moving oxygen and carbon dioxide, the blood also ensures that the tissues are supplied with nutrients. These are transported in the blood plasma to the places in the body where nutrients are needed. In addition, waste is taken away by the blood plasma to be evacuated from the body through the intestines or the bladder.

Immune pathogens

Blood also plays a major role in our defence against pathogens, in particular the white blood cells. Once a pathogen enters the body, the white blood cells ensure that it is defused. If this does not happen, or not quickly enough, we fall ill.

The platelets that are in our blood ensure that it coagulates quickly if we have a wound, so that the bleeding stops. Platelets also act in a similar way if a vessel wall becomes damaged. The platelets form a scab on the wound, enabling the tissue to recover and ensuring that we do not lose too much blood.

How many litres of blood do humans have in their bodies?

The body of a mature person is comprised of around 7% blood. A person weighing 70 kilogrammes has a blood volume of five to six litres. In comparison, a newborn baby has only 300 to 400 millilitres of blood and a pregnant woman 6.5 to 7.5 litres.

Problems with blood Blood loss

Because the blood in our body carries out such important functions, the consequences are often severe if there are problems with the blood. In the event of significant blood loss, there will not be enough red blood cells to transport oxygen. The cells and tissues in the body will then receive insufficient oxygen and will no longer function correctly. Severe blood loss can lead to organ failure and a blood transfusion will be required.

Shortage of blood cells or platelets

In addition to general blood loss, there can also be a specific lack of red or white blood cells or platelets. In the event of a deficiency of white blood cells, the body does not have sufficient defences against pathogens. People with too few white blood cells regularly fall ill. A shortage of platelets means that wounds bleed for longer, which is a particular cause of concern in larger wounds with greater blood loss.

Blood poisoning

In addition to a shortage of blood cells, blood poisoning may occur, which is a serious illness that can lead to death if not treated quickly. Blood poisoning is caused by an infection where the body reacts so violently that there is an inflammatory reaction in the blood. Blood poisoning is accompanied by fever, diarrhoea, abdominal pain and drowsiness, and death can occur in the space of eight to 24 hours.


Blood is an important and indispensable part of our body that has several functions. And to answer the original question: adults have an average of five to six litres of blood in their bodies.



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