Overview of the Heart
The Heart is made up of four chambers. The two upper chambers are known as Atria. Their key function is to receive blood from the body and lungs. The lower Chambers are known as ventricles. Their key function is to pump blood out of the heart towards the body and the lungs. A thick muscular wall called the myocardium surrounds the heart chambers.
The key structures that you need to know and understand are the ventricles, atria, valves and blood vessels in and out of the heart.
The aortais connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs. The vena cavais connected to the right atrium and brings deoxygenated blood back from the tissues of the body. The pulmonary artery is connected to the right ventricle and carries deoxygenated blood to the lungs. Finally, the pulmonary veinsconnect to the left atrium and bring back oxygenated blood from the lungs.
The main function of the heart valves is to stop the black flow of blood. This ensures that there is a one way flow of blood through the heart. There are four valves in the heart: two at the junction between the atria and the ventricles (the atrio-ventricular valves) and the other two at the exit points between the ventricles and the arteries (semi-lunar valves). These semi-lunar valves are in the arterial wall just outside the heart between the right ventricle and the pulmonary artery and between the left ventricle and the aorta. They key function is to prevent the blood flowing back into the heart during contractions (McArdle, Katch, & Katch, 2006)
|Atrio-ventricular Valves||Semi-lunar Valves|
|Tricuspid valve:Located in the right hand side of the heart and it ensures a one way flow of blood from the right atrium to the right ventricle. Mitral or bicuspid valve:Located on the left hand side of the heart and it ensures a one way flow of blood from the left atrium to the left ventricle||Aortic valve:Located between the left ventricle and the aorta and it prevents the back flow of blood into the left ventricle from the aortaPulmonary valve:Located between the right ventricle and the pulmonary artery and it prevents the back flow of blood into the right ventricle from the pulmonary artery|
“Although more than 2000 gallons of blood flow through the heart’s chamber each day, none of its nourishment passes directly into the myocardium. This is because there are no direct circulatory channels within the heart’s chamber leading to its tissues.” (McArdle, Katch and Katch, 1996). Because of this, the heart has its own set of arteries that provide the heart with blood, oxygen and other nutrients. The key function of these arteries is to keep the myocardium (heart muscle) continually supplied with oxygenated blood.
The diagram on page 12 shows the three main arteries that supply the heart. The right and left coronary arteries originate at the aorta at the point where it exits the heart. The left coronary artery then splits into two branches: the circumflex branch which wraps around to supply the left posterior region of the myocardium. The left anterior descending artery continues down the front of the heart to supply the left anterior region.
Majority of blood flow through the coronary arteries occurs during the diastole (resting phase) of the heart. The more time the heart spends in diastole the more blood can be supplied to the myocardium. Therefore a fitter person with a slower resting heart rate will have a better supply of blood to the myocardium. This is an important long-term benefit of cardiovascular training.
The myocardium has virtually no anaerobic capacity and is therefore dependant on blood flow through the coronary arteries. Adequate oxygen supply to the heart is critical. If the blood supply is partially blocked due to a narrowed coronary artery, then this usually results in anginaand the person experiences chest pains when they exert themselves. A complete blockage of a coronary artery will result in myocardial infarction(commonly referred to as a heart attack). The more severe the blockage, the more severe the heart attack, which can result in death.
Narrowing of the coronary arteries is due to hardening of the artery wall and a build up of fatty deposits over time. This progressive condition is known as coronary heart disease (CHD) and is discussed in more detail later.
Most regions of the heart are served by more than one branch of the arteries. So if there is a reduction in blood supply through one of the arteries, then blood supply to the tissue can be maintained through collateral vessels. However, if narrowing occurs in the main stems of the three principle arteries, then the only solution may be surgery to widen the narrowed areas, or to completely bypass them with a coronary artery bypass graft.