The cells in our body constantly need nutrients to maintain their vital process, which are brought to them by the blood.

These nutritional elements are made up of proteins, carbohydrates and fat, broken down into their elemental molecules (proteins, lipids and glycids) as well as minerals, water and vitamins.

Blood CellsThe blood also has the function of transporting oxygen to the cells, and serving as a vehicle for undesirable elements such as carbon dioxide, which must be expelled from the lungs, and urea, which must be eliminated by the kidneys.

The blood is composed of a liquid part, the plasma, consisting of nutritive substances and residual elements of cellular reactions. Plasma also has an organized part, the figurative elements, which are blood cells and platelets.

Blood cells divide into reds and banks.

The Red blood cells These are the red blood cells, cells without nucleus containing hemoglobin, a red blood pigment responsible for the transport of oxygen and carbon dioxide.

The White blood cells they are the leukocytes, true nucleated cells, charged with defending the body. Are they: neutrophils, basophils, eosinophils, monocytes and lymphocytes.

Red blood cells

Red blood cells are 5 million per cubic millimeter.

Leukocytes are from 5 to 9 thousand per cubic millimeter.

Platelets They are cytoplasmic fragments of bone marrow cells, directly implicated in the process of blood coagulation. They number from 100 to 400 thousand per cubic millimeter.


Blood is contained in a closed system of channels (blood vessels) driven by the heart. It leaves the heart through arteries that branch off into arterioles and ends in capillaries, which in turn continue into venules and veins, returning to the heart.

At the capillary level, plasma is accompanied by some lymphocytes and rarely red blood cells, which can leak into the interstitial space, constituting the lymph, which is later reabsorbed by the lymphatic capillaries and then the veins, being reintegrated into the circulation.

The heart is the central point of circulation. From it we have two distinct closed circuits:

Pulmonary Circulation or right or small circulation: goes from the heart to the lungs and returns to the heart. It is intended for gas exchange (carbon dioxide gas).

Systemic Circulation or left or large circulation: goes from the heart to the whole organism and returns to the heart. It is intended for systemic nutrition of all cells.

This content is best described in & #8220; Introduction to the Cardiovascular System & #8221 ;.

Structures of
Cardiovascular system

Blood vessels

Arterial system

Venous system