Blood is a liquid tissue formed by different types of cells suspended in plasma. It circulates throughout our body, through veins and arteries.
Veins carry blood from organs and tissues to the heart, while arteries carry blood from the heart to organs and tissues.
Cells receive blood through smaller blood vessels called arterioles, venules and capillaries.
An adult circulates, on average, six liters of blood.
Functions of Blood
One of the basic functions of blood is the transportation of substances, the highlights of which are:
- Carry oxygen and nutrients to cells;
- Remove leftovers from cellular activities from tissues (such as carbon dioxide produced during cellular respiration);
- Conduct hormones through the body.
Blood plays an important role in defending the body from the actions of harmful agents.
Blood Composition
Blood appears to be a homogeneous liquid, however, when observed under a microscope it can be seen that it is heterogeneous, being composed of red blood cells, white blood cells, platelets and plasma.
Plasma, which accounts for up to 60% of blood volume, is the liquid part in which red blood cells, white blood cells and platelets are suspended. The quantity of each component can vary depending on the person’s sex and age.
Some diseases, such as anemia , can also cause changes in the normal values of blood components.
Red Blood Cells
Red blood cells, also called erythrocytes , are the most abundant cells in humans. They are shaped like a concave disc on both sides and do not have a nucleus.
They are produced by the bone marrow and are rich in hemoglobin , a protein whose red pigment gives blood its characteristic color. It has the property of transporting oxygen, playing a fundamental role in respiration.
White Blood Cells
White blood cells, also called leukocytes, are produced in the bone marrow. They are the body’s defense cells that belong to the immune system.
They destroy foreign agents, such as bacteria, viruses and toxic substances that attack our bodies and cause infections or other diseases. They also play an important role in blood clotting.
In the blood there are different types of leukocytes with different shapes, sizes and nucleus forms: neutrophils, monocytes, basophils, eosinophils and lymphocytes .
Leukocytes are larger than red blood cells, but their number in the blood is much smaller. When the body is attacked by foreign agents, the number of leukocytes increases significantly.
Platelets
Platelets , also called thrombocytes , are not cells, but cell fragments. Their main function is related to the blood coagulation process.
When there is an injury, with ruptured blood vessels, platelets adhere to the injured areas and produce a network of extremely fine threads that prevent the passage of red blood cells and retain the blood.
Platelets are present in every drop of blood and their number is approximately 150,000 to 400,000 platelets per cubic millimeter under normal health conditions.
Plasma
Plasma is a yellow liquid and makes up more than half of the blood volume .
It is made up of a large quantity of water, more than 90%, in which nutrients (glucose, lipids, amino acids, proteins, mineral salts and vitamins), oxygen gas and hormones, and waste produced by cells, such as carbon dioxide and other substances that must be eliminated from the body, are dissolved.
Blood Types
Blood types are blood classification systems. They were discovered in the early 20th century by physician Karl Landsteiner.
For the human species, the most important blood types are the ABO System and the Rh Factor.
In the ABO system , for example, there are four blood types: A, B, AB and O. The possible compatible donation types are:
- Type A : receives from A and O and donates to A and AB
- Type B : receives from B and O and donates to B and AB
- Type AB : receives from A, B, AB and O and donates to AB
- Type O : receives from O and donates to A, B, AB and O
Meanwhile, the Rh Factor works independently of the ABO System, and is related to the production of an antigen located on the plasma membrane of red blood cells.