Chambers of the heart. Right atrium. Left atrium.
The atria are blood-receiving chambers, the ventricles, in contrast, eject blood from the heart into the arteries. The right and left atria are separated from each other by a septum, as well as the right and left ventricles. On the contrary, between the right atrium and the right ventricle there is a message in the form of a right atrioventricular opening, ostium atrioventriculare dextrum; between the left atrium and the left ventricle – ostium atrioventriculare sinistrum. Through these holes, blood during atrial systole is directed from the cavities of the latter into the cavity of the ventricles.
The right atrium, the atrium dextrum, is shaped like a cube. Behind him pour in at the top v. cava superior and v. below. cava inferior, anterior to the anterior to the hollow process – right ear, auricula dextra. The right and left ears cover the base of the aorta and pulmonary trunk. The partition between the atria, septum interatriale, set obliquely, from the front wall it goes back and to the right, so that the right atrium is located on the right and front, and the left – on the left and behind. The inner surface of the right atrium is smooth, with the exception of a small area in front and the inner surface of the ear, where a number of vertical ridges from the comb muscles, musculi pectinati, are visible. At the top of the musculi pectinati end with a scallop, crista terminalis, which on the outer surface of the atrium corresponds to sulcus terminalis. This sulcus indicates the junction of the primary sinus venosus with the atrium of the embryo. On the septum separating the right atrium from the left, there is an oval-shaped recess – fossa ovalis, which is bounded at the top and front by the edge – limbus fossae ovalis. This recess is the remainder of the hole – foramen ovale, through which the atria during the prenatal period communicate with each other. In cases of foramen ovale lasts for a lifetime, as a result of which it is possible to periodically shift arterial and venous blood in the event that the contraction of the atrial septum does not close it. There is a slight elevation between the openings of the upper and lower hollow veins on the back wall, tuberculum intervenosum, behind the upper fossae ovalis. It is believed that he directs the blood flow from the superior vena cava to the ostium atrioventriculare dextrum at the embryo.
From the bottom edge of the hole v. cava inferior to limbus fossae ovalis stretches a crescent-shaped fold, varying in size, valvula venae cavae inferioris. It is of great importance in the embryo, directing blood from the inferior vena cava through the foramen ovale to the left atrium. Below this flap, between the holes v. cava inferior and ostium atrioventriculare dextrum, sinus coronarius cordis flows into the right atrium, collecting blood from the veins of the heart; in addition, small veins of the heart, independently flow into the right atrium. Their small holes, foramina vendrum minimorum, are scattered on the surface of the walls of the atrium. Near the opening of the venous sinus there is a small fold of the endocardium, valvula sinus corondrii. In the lower anterior part of the atrium, the wide right atrioventricular ostium, ostium atrioventriculare dextrum, leads into the cavity of the right ventricle.
The left atrium, atrium sinistrum, is adjacent to the posterior descending aorta and esophagus. On each side, two pulmonary veins flow into it; the left ear, auricula sinistra, bulges anteriorly, bending around the left side of the aortic trunk and pulmonary trunk. In the ear there are musculi pectinati. In the inferior anterior left atrial ventricular opening, ostium atrioventriculare sinistrum, oval in shape leads to the cavity of the left ventricle.