Cardio vascular

The Cardiovascular System



The Cardiovascular System Thomas Secrest

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Reading The cardiovascular system consists of the heart, the arteries and veins, and the blood. Often each element of the system is studied separately, however, we are going to combine all the elements and discuss them together. The core of the cardiovascular system is the heart. The heart is a four chamberedmuscular pump that drives the blood through the circulatory system. The heart is usually said to be about the size of a person’s clinched fist. It is located in the central part of the chest in an area between the lungs anterior to the vertebral column and posterior to the sternum. The space, called the mediastinum, also contains the thymus gland, the trachea, the ascending, arch and descending aortaand the superior and inferior vena cava. The heart is often described as being “two-pumps-in-one.” Before we explain the “two-pumps-in-one” concept we need to detour for a moment and briefly describe the circulatory system. The circulatory system consists of arteries and veins that carry blood out to the organs, tissues and cells of the body and then return the blood to the heart. By definitionarteries carry blood away from the heart and veins carry blood back toward the heart. While it is logical and useful to study the arterial circulation and the venous circulation it is common to subdivide the circulatory system at least once before starting with this approach. The initial subdivision is to divide it into the systemic (to the body) circulation and the pulmonary (to the lungs)circulation. After this subdivision is made, it is much easier to the talk about the various arteries and veins of the systemic or pulmonary circulations. When needed, these two main subdivisions can be further subdivided to provide greater accuracy of description. Some examples of additional subdivisions include the hepatic circulation, cerebral circulation and the coronary circulation. Now we can returnto the “two-pumps-in-one” concept; the heart can be viewed as two pumps – the right side pump drives blood through the pulmonary circulation while the left side pump drives blood through the systemic circulation. Each “pump” side consists of an atrium and ventricle. Use the figure on the right and the below to follow blood flow through the heart. {Blood flow from the systemic veins, through theright atrium and right ventricle and into the pulmonary arteries is shown in blue to indicate deoxygenated blood. Blood flow from the pulmonary veins through the left atrium and left ventricle and into the systemic arteries is shown in red to indicate oxygenated blood.} Blood returns to the right atrium from the veins of the systemic circulation The right atrium pumps blood into the right ventricleThe right ventricle pumps blood into arteries that supply the lungs (pulmonary circulation) Blood passes through pulmonary capillaries and enters pulmonary veins Blood returns to the left atrium from the veins of the pulmonary circulation The left atrium pumps blood into the left ventricle The left ventricle pumps blood into the arteries of the systemic circulation Blood passes through systemiccapillaries and enters systemic veins

The Cardiovascular System Thomas Secrest

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The Valves To control the flow of blood through the heart and to prevent backflow of blood and insure blood flow in only one direction, the heart is equipped with two sets of valves. The first set is called the AV valves or atria-ventricular valves. The valve between the right atrium and right ventricle iscalled the tricuspid valve and the valve between the left atrium and left ventricle is called the bicuspid valve or mitral valve. These vales ensure that blood does not move back into the atria during the powerful contraction of the ventricles. The second set of valves is called the semilunar valves. The valve between the right ventricle and the pulmonary trunk is called the pulmonary semilunar...