THE CARDIOVASCULAR SYSTEM
The Cardiovascular system, comprising both the heart and the blood vessels, circulates blood throughout the body. It carries essential supplies of food and fuel to every living cell and exchanges them for potentially harmful waste products.
The heart is a hollow muscular organ about the size of a clenched fist. Inside, the heart is divided vertically by a muscular wall called the septum. On each side of this wall is an upper chamber (atrium) and a thicker, lower chamber (ventricle). Blood moves through each side of the heart systematically. Deoxygenated blood is delivered into the right atrium. It then enters the right ventricle, from where it is pumped out into the pulmonary artery and to the lungs. Oxygenated blood returning in the pulmonary veins flows into the left atrium. This blood enters the left ventricle and is then pumped into the aorta for circulation.
Blood is made up of plasma, red blood cells (RBC), white blood cells (WBC) and platelets.
In its passage through the body blood is carried in arteries and veins. Most arteries transport oxygenated blood, and most veins transport deoxygenated blood. The largest artery is the aorta. Arteries split into narrow branches called arteriols, which in turn divide into capillaries. It is through the very thin capillary walls that the blood gives up its oxygen and nutrients and receives carbon dioxide and wastes. Deoxygenated blood in the capillaries flows into venules, and then into veins. The two largest veins, the Venae cavae, return this blood to the heart.
To ensure reoxygenation, the circulation has a second “loop”. In this part of the system, blood rich in carbon dioxide travels from the heart along the pulmonary artery to the lungs, where carbon dioxide is exchanged for oxygen breathed in. The newly oxygenated blood is carried back to the heart along the pulmonary vein, the only vein to transport oxygenated blood.
The flow of blood in each side of the heart is controlled by a series of valves. The pumping action of the heart is achieved by the contraction of the cardiac muscle. The rhythm of the heartbeat is regulated by the pacemaker, a concentration of specialized heart tissue. The pacemaker also helps to ensure the correct sequence of activities during each heart beat. The period of contraction (systole) is followed by a period of relaxation (diastole), during which the heart refills. The electrical activity of the heart is monitored as an electrocardiogram (EKG).
Heart disease is the ordinary term used to describe a variety of heart disorders. These include arteriosclerosis, coronary heart disease, coronary thrombosis, hypertension, angina pectoris and many others.