The cardiovascular systemThe cardiovascular system is made up of the heart, blood vessels and blood and its main functions include the transport of blood throughout the body, protection against invading micro-organisms and prevention of blood loss through hemostasis. (Widamaier et al 2011: 5) One of the main organs of the cardiovascular system is the heart; the heart is made up of four chambers. Blood enters the right atrium of the heart from the body through the vena cava, then passes through the tricuspid atrioventricular valve to the right ventricle. Blood is then pumped through the pulmonary semilunar valve out of the heart to the lungs using the pulmonary arteries. It is then oxygenated and returns to the left atrium in the pulmonary veins, passes through the mitral atrioventricular valve to the left ventricle and is then pumped out of the heart into the systematic circulatory system via the semilunar aortic valve to the aorta. (Widamaier et al 2011: 359) The heart is located in the thoracic cavity protected by a sac called the pericardium. The inner wall of the heart is made up of three layers. The outside of the heart wall is called the epicardium. This lubricates the core and prevents friction. The middle and thickest layer of the heart, called myocardium, is a thick muscular layer made of heart muscle that is responsible for pumping blood. The thickness of the myocardium varies throughout the heart, the atria do not need as much myocardium as the ventricles, because the atria only need enough pressure to bring blood to the ventricles, while the Ventricles need enough pressure to pump blood to the lungs and body. . The left ventricle has a thicker layer of myocardium than the right ventricle, because the middle of paper......injury. (Widamaier et al 2011: 354) The cardiovascular system is made up of the heart which pumps blood to the lungs through the pulmonary circulation, the heart muscle through the cardiac circulation and the body systems through the systematic circulation. It is made up of various chambers and valves and its cycle is controlled by an electrical signal from the heart itself. There are different vessels that control blood flow throughout the body. Among them, high-pressure arteries and arterioles originating from the heart. Capillaries with a semi-permeable membrane that allows the exchange of gases, nutrients and wastes between blood and tissues. Also veins with low pressure and containing valves that prevent reflux. All of these elements together perform the main functions of the cardiovascular system; protection, transport and regulation.