Human Blood
Blood is the complex and vital fluid that circulates through a person's heart, arteries, capillaries and veins, carrying essential nourishment and oxygen to all the cells of the body and removing waste products. Blood is a living tissue composed of cellular elements suspended in a watery fluid. Although blood appears to be red liquid, it is actually composed of clear, straw-colored liquid called plasma and billions of cells. The vast majority of these cells are red cells, and these give blood its red color. In addition to the red cells, blood also contains several types of infection-fighting white cells and tiny cell fragments called platelets that are essential for clotting.
On its journey away from the heart, blood carries oxygen from the lungs to the cells throughout the body. In returning to the heart, blood carries carbon dioxide from the cells to the lungs where it is exhaled into the air.
Blood also supplies each individual cell with certain essential nutrients such as proteins, fats and carbohydrates. These nutrients are absorbed by the blood as it passes through the digestive system and delivered to the cells as the major source of the energy required for normal cellular function. Many of the waste products of cellular function are carried by the blood to the kidneys where they are eliminated as urine.
Hormones, which are complex chemicals produced by certain glands and organs to regulate specific body functions, are also transported throughout the body by blood.
Blood also:
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Plays a significant role in maintaining health and warding off infection and disease by helping to carry out the functions of the immune system.
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Is essential to the process that controls and stops bleeding after an injury by carrying special chemicals and proteins that trigger and enable the normal functions of the coagulation system.
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Is crucial in maintaining a normal, steady body temperature by controlling the amount of heat that is released through the skin. When circulation to the skin is increased, the body is cooled by increasing the amount of heat that dissipates through the skin. Conversely, the body is warmed by decreasing blood circulation to the skin, thereby reducing heat loss.
The total blood volume in an average adult ranges from five to seven liters, or about 1.5 gallons, and varies according to height and weight. Approximately 55 percent of the blood in a normal adult consists of a clear, straw-colored liquid known as plasma. The remaining 45 percent consists primarily of the three major categories of blood cells: red blood cells, or erythrocytes; platelets, or thrombocytes; and white blood cells, or leukocytes.
Red blood cells carry oxygen from the lungs to the body's cells and bring carbon dioxide back to the lungs to be exhaled. Red cells are the most commonly transfused part of whole blood.
White blood cells protect the body against infection and disease. Some fight bacteria and others help the body develop immunity to disease.
Platelets help the blood clotting process when a person bleeds. Platelets are used most commonly to help patients receiving treatment for cancer or leukemia.
Plasma, the liquid portion of the blood, transports the blood cells, water and nutrients to all cells of the body. Plasma makes up about 55 percent of the total volume of blood.
As living tissue, red blood cells and white blood cells are responsible for nourishing, cleansing and protecting the body. Since the cells are alive, they, too, need nourishment. Vitamins and minerals keep the blood healthy. All blood cells have a definite life cycle, just as all living organisms do. The various kinds of blood cells make up about 45 percent of blood.
When the human body begins to lose blood through a minor wound, the platelets help cause the blood to clot to control and stop blood loss. Because new blood cells are always being made in the bone marrow, the body can replace the lost blood. When there is excessive blood loss through a major wound, that blood may have to be replaced through a transfusion of blood donated from other people.
Everyone's blood is similar, but not quite the same. There are four major blood groups. Additionally, your blood may have the Rh factor, which makes it even more unique. Blood received through a transfusion must match your own. Patients who are scheduled to have major surgery may, under certain circumstances, make autologous blood donations (donations of their own blood) so that they have a perfect match.
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