Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovsky 2008

Special Part
Cardiovascular system, systema cardiovasculare - Special Part
Heart - Structure of the heart

The human Heart consists of four chambers: two atria (atrium dextrum/sinistrum cordis) and two ventricles (ventriculus dexter/sinister cordis). The atria receive Blood from the Vessels of the SYSTEMIC AND PULMONARY circulations, whereas the ventricles pump it under pressure into the aorta and the pulmonary trunk.

The right atrium (atrium dextrum) has an irregular cubic shape (Fig. 12). The capacity of the right atrium in adults ranges from 100 to 140 ml, and its wall thickness is 2-3 mm. Through the right atrioventricular orifice (ostium atrioventriculare dextrum), it communicates with the right ventricle; this opening contains the right atrioventricular, or tricuspid, valve (valva atrioventricularis dextra, s. valva tricuspidalis).

On the right, the atrium forms a hollow projection known as the right auricle (auricula dextra). Its internal surface is smooth, except for a small area featuring a series of ridges formed by the pectinate Muscles (mm. pectinati). Superiorly, the pectinate muscles on the lateral surface terminate in a border ridge, the crista terminalis, which corresponds externally to the sulcus terminalis. The medial wall of the atrium is smooth and formed by the interatrial septum (septum interatriale). In its center lies a depression, the oval fossa (fossa ovalis), which is bounded anteriorly and superiorly by a thickened margin, the limbus fossae ovalis. In fetuses, the site of the oval fossa is occupied by the foramen ovale, which connects the two atria. Occasionally, this opening fails to close before birth, leading to the mixing of arterial and venous blood—a congenital defect that requires surgical intervention.

The SUPERIOR VENA CAVA empties into the posterior part of the right atrium, while the INFERIOR VENA CAVA enters from below. The opening of the inferior vena cava is guarded by a semilunar valve, the valvula venae cavae inferioris, which is a fold of the endocardium up to 10 mm wide. This valve directs the blood flow toward the foramen ovale. Between the orifices of the caval Veins, the wall of the right atrium bulges to form the sinus venarum cavarum. On the internal surface of the atrium, between the caval openings, There is a small elevation known as the intervenous tubercle (tuberculum intervenosum). The coronary sinus (sinus coronarius), which is provided with a valve (valva sinus coronarii), opens into the posteroinferior part of the atrium.

The right ventricle (ventriculus dexter) resembles a three-sided pyramid in shape (Fig. 12). Accordingly, it has three walls: anterior, posterior, and medial, the latter being formed by the interventricular septum (septum interventriculare). The capacity of the right ventricle in an adult is 150-240 ml, and its wall thickness is 5-7 mm.

The right ventricle is divided into two parts: the ventricle proper and the conus arteriosus dexter, which is located in the upper left region of the ventricle and continues into the pulmonary trunk. The internal surface of the ventricle is uneven, characterized by muscular trabeculae (trabeculae carneae) that diverge in various directions. On the internal wall of the interventricular septum, these trabeculae are poorly developed. Superiorly, the right ventricle presents two orifices: the right atrioventricular orifice (ostium atrioventriculare dextrum) and the opening of the pulmonary trunk (ostium trunci pulmonalis).

As noted previously, the atrioventricular orifice connects the cavity of the right atrium with that of the right ventricle. It is occupied by the right atrioventricular, or tricuspid, valve (valva atrioventricularis dextra s. tricuspidalis), which prevents the retrograde flow of blood back into the atrium during ventricular systole. The tricuspid valve consists of the right fibrous ring (anulus fibrosus dexter) and three cusps: the anterior, posterior, and septal cusps (cuspis anterior, cuspis posterior, et cuspis septalis) (Fig. 12 A).

The bases of the cusps attach to the fibrous ring, while their free edges project into the ventricular cavity. Tendinous cords (chordae tendineae) attach to the free edges and, at their opposite ends, to the papillary muscles (mm. papillares). Based on their Location in the right ventricle, these include the anterior papillary Muscle (m. papillaris anterior) and the posterior papillary muscle (m. papillaris posterior).

The valve of the pulmonary trunk (valva trunci pulmonalis) (Fig. 12 A) prevents the backflow of blood from the pulmonary trunk into the right ventricle. The valve is composed of three semilunar cusps: anterior, right, and left (valvae semilunares anterior, dextra, et sinistra). Small nodules (noduli valvularum semilunarium) are located on the semilunar cusps, facilitating their tight and complete closure.

The left atrium (atrium sinistrum) is cubic in shape (Fig. 13) and forms a pouch on its left side known as the left auricle (auricula sinistra). The left auricle is longer than the right and is demarcated from the atrium by a constriction. The surface of the left auricle features elevations formed by pectinate muscles. The oval fossa is visible on the interatrial septum, while the posterior wall presents the openings of the Pulmonary veins—two on the left and two on the right. In the anteroinferior region lies the oval-shaped left atrioventricular orifice (ostium atrioventriculare sinistrum), which connects the atrial and ventricular cavities. The capacity of the left atrium is 90-135 ml, and its wall thickness is 2-3 mm.

The left ventricle (ventriculus sinister) is conical in shape (Fig. 13) and possesses three walls: anterior, posterior, and medial. The capacity of the left ventricle ranges from 130 to 220 ml, and its wall thickness is 11-14 mm. The internal surface of the ventricle features numerous muscular trabeculae, which are absent on the septum. The left atrioventricular orifice contains the left atrioventricular, or mitral, valve (valva atrioventricularis sinistra, s. mitralis). This valve is also referred to as the bicuspid valve (valvula bicuspidalis). It consists of anterior and posterior cusps (cuspis anterior et posterior). The number of papillary muscles ranges from 2 to 6, with two (anterior and posterior) being the most common. Positioned to the right and posteriorly is the aortic orifice (ostium aortae) (Fig. 12 A), which houses the aortic valve (valva aortae). The aortic valve is formed by three semilunar cusps: the right, left, and posterior cusps (valvulae semilunares dextra, sinistra, et posterior). The ascending aorta is dilated at the site of the valve and exhibits three depressions known as the aortic sinuses (sinus aortae). The region of the ventricle adjacent to the aortic orifice is termed the left conus arteriosus (conus arteriosus sinister).

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Fig. 12. The Heart from the right. Right atrium and right ventricle (opened), after R. D. Sinelnikov

Fig. 12 A. Fibrous rings and heart Valves (after R. D. Sinelnikov)