How much blood in the human body?

How much blood in the human body?

In this  article, we will discuss about human blood by touching the subjects:

  • what is blood? Blood components and blood types;
  • blood circulation; 
  • amount of blood in the human body.

What is blood?

Blood is what we use to call the life maintaining fluid, since it circulates through the body's circulatory system, from heart, arteries, veins to capillaries.

This highly specialised tissue carries out the critical functions of:

  • transporting oxygen and nutrients to the cells in the whole body;

  • taking away carbon dioxide to the lungs to be exhaled;

  • taking waste products from the cells and transporting them to the excretory system to be passed out the body;

  • carrying and important role in the immune system;

  • transporting electrolytes and hormones;

  • maintaing a constant body temperature.


What are the components of the human blood?

The most important components of the blood are red cells, white cells, platelets and plasma, all humans produce these blood components with no regional differences.


Red blood cells, erythrocytes are cells specialised in carrying oxygen from the lungs to all the tissues of the body and transporting carbon dioxide from the cells to the lungs to be exhaled.

They make up 40-50% of the total blood volume and are produced continuously in the bone marrow from stem cells.

The important part of the red cells is the molecule that transports the gases, hemoglobin, an iron containing protein that also gives blood its red colour. If there are not enough red blood cells, or is not enough hemoglobin in the human blood, the person is diagnosed with anemia.


White blood cells, leukocytes are responsible with the immune system. These are a smaller component of the blood and can be found in different other places of the body like the spleen, liver and lymph glands. There are 5 types of white cells that fight infection: Neutrophils, Eosinophils, Basophils, Lymphocytes and Monocytes.

White cells not only fight infection but also help the body heal its wounds by ingesting dead cells, tissue debris, offer protection against allergens and are even involved in protection against cancerous cells.


Platelets, thrombocytes are fragments of cells produced in the bone marrow that are specialised in forming clots to prevent the body from losing too much blood in case of an injury. They are a vital component for coagulation by releasing coagulating chemicals and by interacting with clotting proteins in a cascading manner. 


Plasma is the liquid portion of the blood, representing more than 55%, that carries the other cell components through the body. It is basically a fluid that contains water, sugars, fats, hormones and proteins such as albumin, gamma globulins, fibrinogen and many other components of the blood. When blood is spun in a centrifuge, the blood cells and platelets go to the bottom of the tube and the plasma stays a clear layer on top.


Blood groups:

A blood group also called a blood type, represents the classification of blood based on the presence or absence of antigens and antibodies. Antigens are protein molecules found on the surface of the red blood cells while antibodies are found in plasma. These are the blood's natural defence mechanisms that alert the immune system against foreign substances.

The type of blood is determined by inherited genes and is divided in different groups. One of the most important blood group system is the ABO System:


There are four major blood groups determined by the presence or absence of the two antigens: A and B on the surface of the red cells.

  • Group A - has A antigens on the red blood cells and B antibodies in the plasma.
  • Group B - has B antigens on the red blood cells and A antibodies in the plasma.
  • Group AB - has both A and B antigens on the red blood cells and no antibodies.
  • Group 0 - has no antigens but has both A and B antibodies in the plasma.


In addition to the A and B antigens there is a third antigen called the Rh factor. Each ABO group can be either RhD positive or RhD negative so there are a total of eight different blood types: A RhD positive (A+), A RhD negative (A-), B RhD positive (B+), B RhD negative (B-), AB RhD positive (AB+), AB RhD negative (AB-), O RhD positive (O+), O RhD negative (O-).


Determining the blood type has a high importance in blood transfusions and pregnancies of RhD negative women since some antigens can trigger a patient's immune system to attack the transfused blood.

Do you know how much blood is in your body? Check our Blood Calculator to find out!


Blood circulation:

Blood is circulated around the body  by the pumping force of the heart, through blood vessels. Thecirculatory  system is made of three systems that work together, the heart, lungs and arteries, veins and other vessels.

Arterial blood caries oxygenated blood from the lungs to the rest of the cells while the venous blood carries carbon dioxide to the lungs to be exhaled.


The left ventricle of the heart pumps blood in the systemic circulation to nourish all the tissues and cells, after it reaches them, leaves the oxygen and nutriments. Then the blood loads with carbon dioxide and is sent back to the heart in the right atrium. 


From the right ventricle the blood goes through the pulmonary artery to the lungs where it changes the dioxide to fresh oxygen that is then sent through the pulmonary vein to the left atrium of the heart where it is passed in the left ventricle to be pumped again in circulation.


In the average human, about 7,572 liters of blood travel daily through the 96,560 kilometres of blood vessels. That means about 2,000 gallons of blood that travel about 60,000 miles of vessels every day.


How much blood in the human body? 

Normally blood makes 7-8% of human body weight. The amount of blood in the body depends more on the size than on the height. In adults, this amounts to 4.5- 6 quarts (5-6 litres) of blood. One unit of blood is roughly equivalent to one pint. Men, on average, have 4.5 - 6 quarts of blood while women have 3.5- 4 quarts. 


The total blood volume in the average adult is approximately 60-65 ml/ kilogram body weight. So about 5 litres of blood are present in an average normal human body. Approximately 2.75 to 3 liters of blood is plasma and the rest is the cell component.


Children have slightly more blood, up to 70ml/ kilogram body weight.


Pregnant women's blood volume increases 50% by her 30th week. So if the average blood volume is situated at 5 liters of blood that means by the 30th week of conception the pregnant woman has about 7.5 liters of blood in her blood stream.


People who live at high altitudes, where there is less oxygen in the air, may have up to 1.8 liters more blood.


We hope that all the information on this topic in a single blog place was usefull to you. Enjoy!

Do you know how much blood is in your body? Check our Blood Calculator to find out!

27 Dec, 2014 | 0 comments | 1558 views

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