Heart, in anatomy, hollow muscular organ that pumps blood through the body. The heart, blood, and blood vessels make up the circulatory system, which is responsible for distributing oxygen and nutrients to the body and carrying away carbon dioxide and other waste products. The heart is the circulatory system’s power supply and main organ. It must beat without stopping because the body’s tissues—especially the brain and the heart itself—depend on a constant supply of oxygen and nutrients delivered by the flowing blood. If the heart stops pumping blood for more than a few minutes, death will result. Heart muscles are involuntary muscles, that is, they could function even if the brain doesn’t specifically orders it to function. Heart is essentially composed of different valves and chambers where blood is pumped to different parts of the body. The largest artery can also be found at the heart called aorta.
Four valves within the heart prevent blood from flowing backward in the heart. The valves open easily in the direction of blood flow, but when blood pushes against the valves in the opposite direction, the valves close. Two valves are located between the atria and ventricles.
Although the right and left halves of the heart are separate, they both contract in unison, producing a single heartbeat. The sequence of events from the beginning of one heartbeat to the beginning of the next is called the cardiac cycle. The cardiac cycle has two phases: diastole, when the heart’s chambers are relaxed, and systole, when the chambers contract to move blood. During the systolic phase, the atria contract first, followed by contraction of the ventricles. This sequential contraction ensures efficient movement of blood from atria to ventricles and then into the arteries.
Posted 2011-01-29 and updated on Jan 29, 2011 8:28pm by crisd