Blood components

Blood components

Blood is made up of a mixture of liquid and cells that circulate through the blood vessels of the circulatory system. The liquid part is called plasma and the cells that make up the blood are called red blood cells (erythrocytes), white blood cells (leukocytes) and platelets1.

To understand them better we will explain them separately:


Plasma, as mentioned above, is the liquid part of the blood in which blood cells are suspended. It is the main component since 55% of human blood is plasma. It is composed mostly of water, and the rest is made up of ions, nutrients, wastes and plasma proteins.

Plasma has different functions among them:

  • It acts as a water reserve, since it is able to replenish it in case of lack of water in the body, as well as to absorb it in case of having it in excess.
  • Prevents blood vessels from becoming clogged and helps maintain blood pressure.
  • Regulates body temperature2.


Red blood cells (erythrocytes) are the cells that circulate in the blood in the greatest quantity, representing 40% of the blood volume.
The function performed by erythrocytes is to transport oxygen to the body’s tissues and exchange it for carbon dioxide to transport it to the lungs, where it is eliminated. They do this thanks to hemoglobin, a protein that gives blood its red color.
When the amount of red blood cells is very low, it is called anemia, which means that the blood carries less oxygen than usual, causing tiredness and weakness. When the opposite is the case, there is an increase in the amount of red blood cells and is called erythrocytosis. This would cause the blood to thicken, leading to serious complications such as myocardial infarction or strokes3.


White blood cells (leukocytes) are found in the blood in smaller quantities than red blood cells3. They are part of the immune system providing a defense to our body to fight any infection or disease. The number of white blood cells will increase in case of an infection to improve the defenses.
There are five types of white blood cells:

  • Neutrophils help the body protect itself against infection.
  • Lymphocytes allow the body to defend itself against viral infections, detect and destroy some cancer cells.
  • Monocytes help defend against many infectious microorganisms.
  • Eosinophils eliminate parasites, destroy cancer cells and participate in allergic reactions.
  • Basophils participate in allergic reactions.

When the number of white blood cells is low, it is called leukopenia, resulting in an increased likelihood of infection. On the other hand, if the number is higher, it is called leukocytosis, thus indicating an infection, inflammation or leukemia2.


Platelets are the smallest blood cells. They are part of the coagulation process as they help heal wounds by forming blood clots and repair blood vessels. When the number of platelets in the blood is very low, it is called thrombocytopenia, leading to the appearance of bruising on the skin and abnormal bleeding. When the amount is excessive, it is called thrombocythemia, leading to excessive coagulation and possible problems in the blood vessels, causing a transient ischemic attack or hemorrhaged3.





  1. “Sangre: MedlinePlus en español.” (accessed Nov. 30, 2022).
  2. “¿Cuáles son los Componentes de la Sangre? | Roche Pacientes.” (accessed Nov. 30, 2022).
  3. “Componentes de la sangre – Trastornos de la sangre – Manual MSD versión para público general.” (accessed Nov. 30, 2022).

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