Arterial blood (red, oxygen-rich blood) flows from the heart to eachÂ part of the body to provide oxygen and nutrients. The venous bloodÂ (blue, oxygen-poor blood) returns from the body to the heart. TheÂ blood then travels through the lungs to exchange carbon dioxide forÂ new oxygen. The heart is a pump which moves the blood. The arteriesÂ and veins are the pipes through which the blood flows. Â The lungsÂ provideÂ a place to exchange carbon dioxide for oxygen.
THE CHAMBERS OF THE HEART
The heart is a hollow, muscular organÂ which functions as a pump for the movementÂ of blood through the body. TheÂ flow of blood through the four chambersÂ of the heart is regulated by valves.Â The heart valves function like one-wayÂ doors which allow blood flow throughÂ in the forward direction but preventÂ the backward flow of blood. VenousÂ blood returns from the body to the rightÂ side of the heart which pumps the bloodÂ to the lungs. The oxygen-rich blood returns from the lungs to the leftÂ ide of the heart.
The left side of the heart pumps blood to the entire body. As youÂ would expect, the left side of the heart must generate a muchÂ greater pressure to pump the blood to the body. On the left side theÂ valves are called mitral and aortic valves. The mitral valve connectsÂ the receiving chamber from the lungs, the left atrium, with theÂ pumping chamber, the left ventricle. The aortic valve controls theÂ flow of blood out of the heart into the aorta, the largest artery of theÂ body which then gives rise to all the other arteries.
THE CORONARY ARTERIES
The first branches of the aorta are arteries toÂ the heart muscle itself. There are two main coronary arteries: the left main (LM) and rightÂ coronary arteries (RCA). The left main coronary artery divides into two mainÂ branches: the left anterior descendingÂ (LAD), which runs down the front ofÂ the heart, and the circumflex arteryÂ (CX) which runs behind the heart.Â Branches of the LAD are called diagonalarteries and branches of the circumflex are called obtuse marginalarteries(OM). The right main coronary artery travels on the right side ofthe heart and gives off the posterior descending artery (PD).