Human Body Essays - Circulatory System, Medicine, Health, Angiology

Human Body Essays - Circulatory System, Medicine, Health, Angiology Human Body In the Beginning Within a month of conception, the cluster of cells that will, in the course of time, become a human being begins throbbing, signaling the development of a primitive heart. Scarcely four weeks more pass before an intricate network of veins and arteries the size of a pea forms and subdivides into a tiny replica of the four chambers that will one day make up the adult heart. As the fetus grows, so does its vitally important circulatory system. Although most of the functions of the heart remain dependent upon the mother throughout the entire pregnancy, in the latter stages the organ becomes strong enough to beat on its own. Even so, until birth the baby is cared for and nourished through the mother's placenta. An umbilical cord provides a supply line that furnishes food and oxygen for the baby, and also removes waste. When at last the birthing moment arrives, the baby emerges a separate individual; almost as soon as its first cries are sounded, its pulmonary and circulatory systems undergo a change that renders them self-sufficient. How it Works Technically speaking, the circulatory system is a masterpiece of organic activity. Composed of a network of 60,000 miles of blood vessels and a pintsized, powerhouse pump known as the heart, it services more than 2,000 gallons of blood per day, feeding and replenishing other organs and making life possible. In an adult, the heart is normally an 11 - ounce, fistsized organ that literally pushes blood through arteries, veins and capillaries. It does this by means of muscular contractions sparked by electrical impulses from the heart's pacemaker (sinoatrial node). All of the cells within each of the chambers magically work on cue. First, the right side sends blood to the lungs. There carbon dioxide is removed and oxygen is added, turning the blood a bright red color. Then the blood is pumped to the left side of the heart and sent via the aorta to the rest of the body. To survive, each of the body's approximately 1 billion cells must be nourished. This is the job of the blood, with the heart and vessels acting as facilitators. After depositing the necessary nutrients with each of the cells, the blood returns to the heart, carrying with it waste products it has picked up along the way. These are eliminated through a filtering process in the lungs and kidneys. By now the supply of oxygen within the blood is nearly exhausted, and it is time to restock its supplies and begin the journey again. Incredibly, the whole process has taken just 20 seconds. During the course of an average life, the heart pumps tens of millions of gallons of blood. It is estimated that the amount would easily fill a 24-foot-wide cylinder to a height greater than the Empire State Building. Perhaps more impressively, the circulatory system has the computer-like ability to direct greater and lesser amounts of blood to various areas of the body according to their immediate needs. This explains why athletes often forego eating just prior to a match. During the process of digestion, the gastric organs require more blood to complete their work. As if that weren't enough, the heart is also wired through the nervous system to respond to a large variety of physical and emotional stimuli. Witness the quickening of the heart at the touch of a loved one. What Can Go Wrong Most circulatory problems are caused by a blockage in an artery, which is known as atherosclerosis or hardening of the arteries. No one knows for sure why this happens, but the prevailing theory states that something causes the protective inner lining of an artery wall to be injured. Once impaired, the collagen in the lining is exposed. That, in turn, attracts platelets and toxic substances from the bloodstream, which enter the artery wall. Eventually, the process leads to a buildup of debris, narrowing of the artery and finally, blockage. Interestingly enough, although the heart has a continual flow of blood streaming in and out of its chambers, it is unable to take the nourishment it needs from this source. Rather, it must rely on its own miniature circulatory system, which branches off from the aorta or main channel. Here tiny but extremely important vessels called coronary arteries provide the means to feed the heart. Like other arteries, they are also subject to blockage. And herein lies a potential and fairly common tragedy, because when coronary arteries cease to function as they should, the heart is deprived of