The Anatomy of The Heart

Figure 2: The Basic Anatomy of the Heart (Martini et al., 2006)

The heart is located at the center of the anterior chest cavity and is responsible for the successful functioning of the pulmonary and systemic circulation in the human body. Human hearts have developed into a four chambered system, which allows for the most efficient functioning of these to circulations and is a result of many years of evolution.The cardiac valves in the heart are composed of a core of dense fibrous connective tissue which contains collagen and elastic fibers on both of the endothelial layers of the valve. The anatomy of the heart is quite complex and is a reflection of the job that it performs day in and day out for us, however I will discuss the main anatomical aspects.

Right Atrium
Receives blood from the systemic circulation (deoxygenated blood) from the superiorinferior vena cava.
Blood Collects and is then passed onto the right ventricle.

Right Ventricle
Blood moves from the right atrium through the tricuspid (AV) valve and closes after to prevent any backflow.
Blood is then transported through the pulmonary (semilunar) valve to the pulmonary trunk where blood flows to the left and right pulmonary arteries to be re-oxygenated in the lungs.

Left Atrium
Oxygenated blood is fed into the atrium from the left and right pulmonary veins. This has similar structure to the right atrium, but there is a greater pressure difference.

Left Ventricle
Blood moves in through the mitral (AV) valve from the left atrium. This is much thicker than the right ventricle, has greater muscle tone, although pumping same volume of blood, mainly due to the high pressure required for systemic circulation. Blood then leaves the left ventricle through the Aorta.

Figure 3: Coronary Angiography showing the coronary arteries filling with blood. Obtained from Wikipedia.

Coronary Arteries
Although the heart pumps blood to the entire body, it does not directly pump blood to itself. This is the job of the coronary arteries which supply blood to the muscle tissue of the heart. These originate from the base of the aorta and each time the heart contracts the blood moves through these. Coronary arteries often become clogged with plaques and can require angiography to determine blockages and if surgery is required. The coronary arteries are composed of three main layers of cells: the tunica intima, tunica media, and the tunica adventitia. The tunica intima composes the innermost endothelial layers. The tunica media contains the smooth muscular layers which are responsible for constriction/dilation. The tunica adventitia consists of the connective tissue (elastin and collagen) within the vasa vasorum.

Cardiac Physiology
The heart beats through the proper functioning of the action potential system of the Sinoatrial Node (In the right atrium) which contains pacemaker cells that send an action potential to the Atrioventricular Node (Bottom of right atrium). The bundle branches further allow conduction of the action potential and branch out into the Purkinje Fibers of the right ventricle. The electrical impulses are autonomically controlled by the nervous system.

Information in this section obtained from Martini et. al, 2006.