Heart internal structure, arteries and veins

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The Internal Structure of the Heart

The heart is a hollow structure mainly composed of a specialized muscle the myocardium. It lays in the middle mediastinum between the lungs and functions as a muscular pump that keeps the blood circulating through the body (Theodora.com, 2007). The heart is divided in a left and a right half by the septum, a muscular wall (University of Western Cape, n.d; Comeau, n.d.). Each half has two cavities. The upper one, the atrium, receives the blood that comes to the heart and the bottom one, the ventricle, pumps the blood out of the heart (University of Western Cape, n.d.). The segment of the septum that divides the atriums is called the atrial septum (or interatrial groove) and the segment of the septum that divides the ventricles is called the ventricular septum (Theodora.com, 2007).

The right half of the heart circulates deoxygenated blood (University of Western Cape, n.d.). The inferior vena cava carrying oxygen-deprived blood from the lower parts of the body and the superior vena cava carrying oxygen-deprived blood from the head, neck, chest and arms end at the right atrium (National Heart and Lung Institute (NHLI), 2010). The right atrium also receives deoxygenated blood from the heart through the coronary sinus (University of Western Cape, n.d.). The right atrium is located in the broader part of the heart and has a relative thin wall of muscle compared to the ventricle (University of Western Cape, n.d.). It pumps the deoxygenated blood to the right ventricle through the atrioventricular valve (Comeau, n.d.).
The right atrioventricular valve is called tricuspid because of its three valves (University of Western Cape, n.d.). These valves "are formed by duplicatures of the lining membrane of the heart, strengthened by intervening layers of fibrous tissue" (Theodora.com, 2007, ¶ 30). Once the blood leaves the atria, this valve closes preventing the backflow of the blood from the ventricle to the atrium (Comeau, n.d.). Chordae tendineae, a series of strong fibrous string, attach the valves to the ventricle muscle preventing the valves from inverting (Comeau, n.d.; Theodora.com, 2007).
From the right ventricle, the blood is pumped to the pulmonary artery through semilunar valves (NHLI, 2010). These three semilunar valves, called as a group the pulmonary valve, are formed by "duplicatures of the lining membrane, strengthened by fibrous tissue" (Theodora.com, 2007, ¶ 32). The pulmonary valve opens into the vein and once the ...