*4.3.1 The right part of the heart*

This section is made up of the right atrium and the right ventricle. The wall of the right atrium is quite thin, and this chamber remains under low pressure [24]. The

#### *Perspective Chapter: Physiology and Pathology of the Cardiovascular System DOI: http://dx.doi.org/10.5772/intechopen.108355*

right atrium carries the pacemaker called the SA (sinoatrial) node, which generates cardiac impulses, as well as the AV (atrioventricular) node, which transmits electrical signals to the ventricles [22]. This right atrium collects the deoxygenated (venous) blood from the whole body via the superior and inferior vena cava and the coronary sinus [3]. This right atrium is connected to the right ventricle via the tricuspid valve, through which deoxygenated blood enters the right ventricle from the right atrium. The pulmonary trunk, which originates in the right ventricle, transports the deoxygenated blood from the right ventricle to the lungs, where it is oxygenated [24]. The right ventricle has a thicker wall than that of the right atrium, but it's less muscular compared to the left ventricular wall.

#### *4.3.2 Left part of the heart*

This part is made up of the left atrium and the left ventricle. The left atrium is a low-pressure and thin-walled chamber [24]. Pulmonary veins deliver the oxygenated blood from the lungs to the left atrium, from where the blood moves to the left ventricle via the bicuspid or mitral valve [24]. The arterial blood is pumped by the left ventricle throughout the body via the systemic aorta.

However, the two right chambers are detached from the left ones by a constant divider, the ventricular section of which is known as the interventricular septum whereas the atrial portion is called the interatrial septum [3]. The interatrial septum is fibrous in nature, but the interventricular septum possesses dual structural characteristics, with the upper one-fourth segment being fibrous and the lower three-fourth section being muscular.

#### **4.4 Valves of the heart**

The human heart possesses four valves, each with a distinct function. Two of them are situated within the junction of the atria and the ventricles. These two valves are termed as the atrioventricular valves. On the other hand, the remaining two valves are located at the aperture of blood vessels originating from the ventricles, i.e., the pulmonary trunk and systemic aorta. These two valves are termed as semilunar valves. Four of these heart valves ensure the unidirectional flow of blood across the heart [26].

#### *4.4.1 Atrioventricular valves*

The right atrioventricular orifice is shielded by the tricuspid valve, which is composed of three cusps or flaps, i.e., infundibular or anterior cusp, medial or septal cusp, and marginal or posterior cusp [3]. Conversely, the left atrioventricular orifice is protected by the bicuspid valve, which is composed of two valvular cusps, namely, the anterior cusp and the posterior cusp [3]. This bicuspid valve is also known as the mitral valve because of its similarity to the miter of a bishop. The cusps of both of these valves are triangular in appearance and are linked to the edges of the fibrous or dense connective tissue surrounding the atrioventricular openings.

#### *4.4.2 Semilunar valves*

The aperture within the pulmonary artery and the right ventricle is guarded by the pulmonic semilunar valve, while the opening between the systemic aorta and the left

ventricle is guarded by the aortic semilunar valve that is stronger and larger compared to the other one [3]. Both of these valves have a shape that resembles a half moon, because of which these are referred to as semilunar valves. These valves are composed of three cusps. The pulmonary semilunar valve is composed of the left anterior cusp, right posterior, and left posterior cusp; whereas the aortic semilunar valve is made up of the right anterior cusp, right posterior, and left posterior cusps, respectively [3].
