The Circulatory System Essay -- essays research papers

The Circulatory System   Ã‚  Ã‚  Ã‚  Ã‚  The circulatory system in anatomy and physiology is the course taken by the blood through the arteries, capillaries, and veins and back to the heart. In humans and the higher vertebrates, the heart is made up of four chambers the right and left auricles, or atria, and the right and left ventricles. The right side of the heart pumps oxygen-poor blood from the cells of the body back to the lungs for new oxygen; the left side of the heart receives blood rich in oxygen from the lungs and pumps it through the arteries to the various parts of the body. Circulation begins early in fetal life. It is estimated that a given portion of the blood completes its course of circulation in approximately 30 seconds.   Ã‚  Ã‚  Ã‚  Ã‚  Pulmonary circulation is where the blood from the entire body is transported to the right auricle through two large veins. The superior vena cava and the inferior vena cava. When the right auricle contracts, it forces the blood through an opening into the right ventricle. Contraction of this ventricle drives the blood to the lungs. Blood is prevented from returning into the auricle by the tricuspid valve, which completely closes during contraction of the ventricle. In its passage through the lungs, the blood is oxygenated, that is, then it is brought back to the heart by the four pulmonary veins, which enter the left auricle. When this chamber contracts, blood is forced into the left ventricle and then by ventricular contraction into the aorta. The bicuspid, or mitral, valve prevents the blood from flowing back into the auricle, and the semilunar valves at the beginning of the aorta stop it from flowing back into the ventricle. Similar valves are present in the pulmonary artery.   Ã‚  Ã‚  Ã‚  Ã‚  The aorta divides into a number of main branches, which in turn divide into smaller ones until the entire body is supplied by an elaborately branching series of blood vessels. The smallest arteries divide into a fine network of still more minute vessels, the capillaries, which have extremely thin walls; thus, the blood is enabled to come into close relation with the fluids and tissues of the body. In the capillaries, the blood performs three functions then it releases its oxygen to the tissues, it furnishes to the body cells the nutrients and other essential substances that... ...itiating the heartbeat. The contraction then spreads over the auricles in the septum between the auricles, it excites another node called the auriculoventricular node. The auriculoventricular bundle conducts the impulse from this node to the muscles of the ventricles, and in this way contraction and relaxation of the heart are coordinated. Each phase of the cardiac cycle is associated with the production of an electrical potential that can be recorded by electrical instruments to produce a reading known as an electrocardiogram.   Ã‚  Ã‚  Ã‚  Ã‚  Circulation of the blood in superficial capillaries can be observed under the microscope. The red blood cells can be seen moving along rapidly in the middle of the blood current, while the white cells advance more slowly along the walls of the capillaries. The capillaries present a far larger surface with which the blood comes in contact than do other blood vessels end because they consequently offer the greatest resistance to the progress of the blood, they have a great influence on the circulation. Capillaries expand when temperature rises and help to cool the blood then they contract in cold and help preserve internal heat.