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Cardiovascular System
The cardiovascular system is the term used to collectively describe the heart, blood, and vessels in an organism. The cardiovascular sustem, also refered to sometimes as the circulatory system, comes from the Greek kardia for "heart," and the Latin vasculum, for "small vessel."
Human Heart and Blood Flow
The human cardiovascular system is comprised of a heart, vessels that carry the blood from the heart to the rest of the body, and the blood itself. The human heart consist of four different chambers: two atria and two ventricles. The atrium and ventricles that are located on the right side of your body are called the right heart while the atrium and ventricles that are located on the left side of your body are called the left heart.
An atrium receives blood from the body and pumps it into a more muscular chamber, the ventricle. The ventricle pumps the blood to the lungs where gas exchange occurs and to other parts of the body once oxygenated. The right heart is responsible for sending blood through the pulmonary circuit and the left heart is responsible for sending blood through the systemic circuit. Located in the heart are different valves that prevent the backflow of blood. The atrioventricular valves, located between the atria and ventricles, stop blood from flowing back into the atria when the ventricles contract. The pulmonary valve and the aortic valve are positioned between the ventricles and the major arteries to prevent blood from flowing back into the ventricles. Deoxygenated blood starts its circulation through the heart by entering the right atrium from the superior or inferior vena cava. The superior vena cava brings blood in from the upper portion of the body while the inferior vena cava collects blood from the lower portion. At the contraction of the right atrium, blood travel through an atrioventricular valve and into the right ventricle. After the right ventricle is filled with blood it contracts, pumping the blood into the pulmonary artery, which takes the blood to the lungs. After gas exchange has occurs in the lungs, blood returns to the heart via pulmonary veins. The oxygenated blood enters at the left atrium where it collects before entering the left ventricle through an atrioventricular valve. The muscular walls of the left ventricle exert a large force on the ventricle forcing the blood from the ventricle, through the aortic valve, and into the aorta where the oxygenated blood will circulate throughout the rest of the body. Both sides of the heart contract at the same time. The cardiac cycle consist of the contraction of the two atria followed by the contraction of the two ventricles and a period of relaxation. Contraction of the ventricles is called ventricular systole, and the relazation of the ventricles is called ventricular diastole.