Blood is a specialized connective tissue common to all animals, carrying nutrients and removing waste throughout the bodies of living organisms. Blood is circulated by hydraulic action, pumped by the essential muscle, the heart. The blood vessels, veins and arteries are a complex system of differently-sized circulatory lines that keep each organ and bodily system functioning.
Formed elements are the simplest substances or constituent parts of a system; in the case of blood, they are the non-fluid elements. Blood is typically about 80 percent water, which can be best thought of as the medium of transmission for the formed elements of blood. All formed elements in blood are generated from bone marrow.
Red Blood Cells
Also called erythrocytes, red blood cells are the most common formed elements in blood, giving blood its distinct coloration. Red blood cells are the primary means of transporting oxygen into the body's tissues and are comprised primarily of hemoglobin, which bonds readily with oxygen. It is estimated that 25 percent of all cells in the human body are red blood cells.
White Blood Cells
Also called leucocytes, white blood cells are the primary cells of the immune system, which has the important task of defending the body against viral, bacterial and parasitic attacks. Many of these attacks specifically strike white blood cells first in order to exhaust the immune system, preparing the body for a worse attack. However, many symptoms of illness are the consequence of the immune system fending off an attack.
Platelets are irregularly-shaped cell fragments that serve the primary function of hemostasis, which helps maintain the consistency of blood as well as keeping it inside of vessels, should they ever be punctured. Blood clots are a key part of the body's ability to repair and heal itself, self-sealing from the released pressure when a vessel is cut.
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