You already know that blood carries nutrients, respiratory gases, hormones and metabolism residues.
Although the blood appears to be a completely homogeneous red liquid, under the optical microscope we can see that it consists basically of: plasma, red blood cells, white blood cells and platelets.
Plasma is the liquid portion of the blood, contains water (over 90%), various proteins and minerals, glucose and vitamins, among other substances.
Red blood cells are also called erythrocytes or red blood cells. See again how these cells look in the photo.
Red blood cells are the most numerous blood cells. In humans, there are about 5 million of them per cubit millimeter of blood. They are produced in the red bone marrow of the bones. They have no core and are concave disc shaped on both sides. The discoid shape and concavity on both sides ensure a relatively large surface for the uptake and distribution of oxygen gas.
The red color of the red cells is due to the presence of the hemoglobin pigment. Oxygen gas combines with hemoglobin to form oxyhemoglobin. In tissues, this combination is undone and oxygen gas passes into the cells. Thus, red blood cells promote the transport and distribution of oxygen gas to all parts of the body.
Red blood cells last about 90 to 120 days. After this period they grow old and die and the bone marrow itself is replaced.