At the end of its life period, the "worn out" RBC is removed by the spleen and the
"pieces," particularly the iron, are salvaged by the liver. (para 10-11a)
The second category of formed elements of the blood is the white blood cells.
Phagocytic WBCs actively attack foreign substances and engulf them in a
process called phagocytosis. When the WBCs are overcome and die, their bodies
accumulate to form a substance called pus.
The lymphocytes are involved with the immune system of the body, including the
The third type of formed element in the blood is the platelets. These are
fragments of former cells. They are very important in the clotting process.
After the formed elements and fibrinogen are removed from the blood, the
One very important transport function of the blood is to carry gases back and
forth between the lungs and the individual cells of the body. The sites of exchange are
the alveoli and the individual body cells. At these sites, a gas moves from the area
where its concentration is higher to the area where its concentration is lesser.
Near the alveoli, most of the dissolved oxygen is rapidly picked up by the
hemoglobin of the RBCs. Thus, the RBC is the main transporting element for oxygen.
Produced during metabolic oxidation is carbon dioxide. It passes through the cell
membrane and the capillary wall to become dissolved in the plasma of the blood.
Through the action of an enzyme, most of this gas is transformed into bicarbonate ions.
The escape of blood from damaged blood vessels is called hemorrhage.
The first response to a cut or ruptured vessel is contraction (spasm) of the blood
If the hole is small, a plug formed by clumping of the platelets may stop the
A complicated process for sealing off holes or ends of blood vessels is called
coagulation or clotting. In this process, the blood forms a solid mass call a blood clot.
After a number of steps, the protein fibrinogen is converted into sticky strands of fibrin.
The resulting meshwork traps RBCs and plasma and thus seals the opening.