Right atrium (RA)
The right atrium (RA) is situated in the superior right corner of the heart above the right ventricle (RV). The systemic circulation ends in the right atrium, as deoxygenated blood from the tissues of the body enters it through the superior and inferior vena cava, and the coronary sinus (collects venous blood from the heart itself).
The right atrium has a cuboid shape, therefore it has six walls: superior, inferior, anterior, posterior, lateral and medial.
- The superior vena cava (SVC) opens to the superior wall of the RA.
- On the inferior wall, the right atrioventricular orifice is located, which is an oval aperture between the RA and the RV.
- On the anterior wall, the right auricle (right atrial appendage) is placed. The main function of the right auricle is to increase the volume of the right atrium. The muscular layer of the heart creates parallel ridges in the anterior wall and the auricle called the pectineal muscles.
- The opening of the inferior vena cava (IVC) is located in the posterior wall of the RA.
- On the lateral wall, the pectineal muscles are located.
- The medial wall is formed by the interatrial septum. The interatrial septum has an oval fibrous depression called the fossa ovalis that covers the foramen ovale during fetal development. Around the fossa ovalis is an oval margin named the annulus ovalis or limbus of the fossa ovalis. On the medial wall, also small openings for the smallest cardiac veins can be seen.
Between the medial and posterior walls there is a small opening for the coronary sinus to the right atrium. The coronary sinus collects venous blood from the heart muscle and is protected by a semicircular fold of the lining membrane of the auricle, called the valve of the coronary sinus.