The heart and circulatory system make up your cardiovascular system. The heart works as a pump that pushes blood to the organs, tissues, and cells of the body. Blood delivers oxygen and nutrients to every cell and removes the carbon dioxide and waste products made by those cells. Blood is carried from your heart to the rest of your body through a complex network of arteries, arterioles, and capillaries. Blood is returned to the heart through venules and veins. If all the vessels of this network in your body were laid end-to-end, they would extend for about 60,000 miles (more than 96,500 kilometers), which is far enough to circle the earth more than twice! (www.innerbody.com; www.texasheartinstitute.org).
The circulatory system carries blood to all part of the human body. The one that carry the oxygenated blood away from the heart are the arteries, and the one that carry a poor oxygenated blood back to the heart are the veins
In pulmonary circulation, though, the roles are switched. It is the pulmonary artery that brings oxygen-poor blood into your lungs and the pulmonary vein that brings oxygen-rich blood back to your heart (Alforn and Hill, 2003).
In the diagram, the vessels that carry oxygen-rich blood are colored red, and the vessels that carry oxygen-poor blood are colored blue.
There were twenty (20) major arteries make a path through the tissues in the body, they will branch in a smaller arteries called the arterioles. Arterioles further branch into capillaries, where the oxygen and nutrients exchange is taking place (Schunke, 2006). Most capillaries are thinner than a hair. In fact, many are so tiny, only one blood cell can move through them at a time. Once the capillaries deliver oxygen and nutrients and pick up carbon dioxide and other waste, they move the blood back through wider vessels called venules. Venules eventually join to form veins, which deliver the blood back to your heart to pick up oxygen. It serves as the communicator between the arteries and the veins. In addition to being the transporters of blood products, capillaries allow for waste products to enter. In this way they perform an important function because waste is ultimately transported out of the body through this interchange (www.wisegeek).
Arterial walls are composed of elastic tissue and smooth muscle. It is their elastic nature and the presence of substantial muscle tissue that allows them to expand and contract as the heart beats. This allows them to even out the increase in pressure caused by each beat (www.jonbarron.org)
Veins are thinner walled than arteries and have less elastic tissue, and much, much less smooth muscle tissue. Instead, veins make use of valves and the muscle contraction of your body’s major skeletal muscles to squeeze blood along. This is the reason one asked to get up and walk around on a long plane flightto prevent blood from pooling in the legs. As a side note, the lack of muscle in the walls of veins makes them more susceptible to bleeding when injured since there is no muscle to clamp down (www.jonbarron.org).
Blood is essential to transport oxygen and nutrients to the tissues; carbon dioxide and other waste product of the cell metabolism to the excretory organs; and leukocytes, hormones, and anti-bodies to various locations in the body. The volume of blood which varies with the size of the individual, is about five (5) quarts in the average man. Almost half of the blood consists of cellular elements; red cells, white cells, and platelets suspended in a viscous fluid called blood plasma. But in addition to the water, plasma contains salts, sugar (glucose), and other substances. And, most important, plasma contains proteins that carry important nutrients to the bodys cells and strengthen the bodys immune system so it can fight off infection (Crowley, 2009).
Blood is actually a tissue. It is thick because it is made up of a variety of cells, each having a different job. In fact, blood is actually about 80% water and 20% solid. We know that blood is made mostly of plasma (contains a variety of proteins and many other small molecules and ions). But there are 3 main types of blood cells that circulate with the plasma (Wilhelm. et. al., 2001).
Platelets, which help the blood to clot. Clotting stops the blood from flowing out of the body when a vein or artery is broken. Platelets are also called thrombocytes.
Red blood cells, also called as the erythrocyes which carry oxygen. Of the 3 types of blood cells, red blood cells are the most abundant. In fact, a healthy adult has about 35 trillion of them. The body creates these cells at a rate of about 2.4 million a second, and they each have a limited life span of about 100 to 120 days (Marieb, 2006).
White blood cells, ward off infection. These cells, which come in many shapes and sizes, are vital to the immune system. When the body is fighting off infection, it makes them in ever-increasing numbers. Still, compared to the number of red blood cells in the body, the number of white blood cells is low. Most healthy adults have about 700 times as many red blood cells as white ones. White blood cells are also called leukocytes. Types of white blood cells are the neutrophil, eosinophil, basophil, monocytes, B and T lymphocyes (Gordon and Golany, 2006; www.texasheartinstitute.org).