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Blood Type
Blood type refers to the presence or absence of chemical molecules on red blood cells. These molecules can instigate antibody reactions and are therefore antigens. Red blood cells can have one, both, or neither of the two antigens named “A” and “B.” Blood with only A antigens or only B antigens is called type A or type B, respectively. Blood with both A and B antigens is called typeAB, and blood with neither is type O. Likewise, people with type B blood have alpha (or anti-A) antibodies that assail A antigens. Type AB blood has both antigens but neither antibody, and type O blood has neither antigen but both antibodies. If type A blood from one person is given to another person with type B blood, the blood will clump due to a process called agglutination, as the alphaantibodies battle the B antigen. After clumping, the red blood cells will rupture in a process called hemolysis, which can lead to serious consequences, such as kidney dysfunction, chills, fever, and even death. Type AB-positive blood is frequently called the “universal recipient.” Type AB blood has neither alpha nor beta antibodies, which means that any blood can be introduced without the chance of anantibody attack by the recipient’s blood. The recipient does not have to worry about antibodies from the donor blood, because the amount of donated blood is small, becomes diluted in the recipient’s blood, and presents no threat. At the opposite end of the spectrum, type O blood is known as the “universal donor.”
Blood Vessels: The Transportation
As previously described, the blood is not justred liquid. It is filled with millions of cells, each with a specific job to do. The circulatory system in a single adult human being comprises some 60,000miles of blood vessels. Most people can see at least a fewof themjust under the skin of the wrist. The vast majority is much smaller than those visible vessels, and has diameters of less than one three-thousandths of an inch (about 10 microns).Blood vessels are associated with one of three major groups: the arterial system, the venous system, or the capillary system.The capillaries take over when the blood reaches its destination, and serve as the exchange vessels between the blood and the lungs, or between the blood and the body tissues.When the exchange is complete, the blood moves from the capillaries into the vessels of the venoussystem, which directs the blood back to the heart to begin another route either to and from the lungs, or to and from the body tissues. The heart-to-body tissues-to-heart circuit is called the systemic circulation and allows tissues to take up oxygen and other materials transported in the blood. Overall, the blood travels more or less in two loops, one from the heart to the lungs and back, and asecond from the heart to the body tissues and back to the heart.
Arterial System
The main function of the arterial system is to carry blood away from the heart and either to the lungs to pick up oxygen, or to other body tissues to drop off nutrients, oxygen, hormones, or other needed substances. The arterial system works much as a road system does: travelers use superhighways to get quickly to ageneral region, then take smaller freeways and finally side roads to reach a specific destination. In the case of the arterial system, the blood moves along main arteries, then into smaller arteries and even smaller arterioles. The specific destination of the blood cells is a set of capillaries in the lungs or in some other body tissue. also known as coronary heart disease, occurs when plaque buildsup inside the arteries that supply the muscles of the heart with blood. This plaque buildup makes it harder for blood to get to the right areas of the heart. Plaque is composed of substances found in the blood, like fat and cholesterol. Plaque buildup results in a condition called atherosclerosis. Certain factors increase the risk of developing CAD:
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