Right Atrium
Right Atrium
Blood first enters the heart through the right atrium via three vessels: the superior and inferior venae cavae, which deliver blood from the body, and the coronary sinus, returning blood from the heart’s walls.
The superior vena cava enters the upper posterior part of the right atrium, while the inferior vena cava and the coronary sinus enter the lower posterior part.
Blood flows from the right atrium to the right ventricle through the right atrioventricular orifice, sealed by the tricuspid valve during ventricular contraction.
Sulcus Terminalis
If we take a closer look at the right atrium, we can observe that on the outside, there is a groove that starts next to the opening of the superior vena cava and continues towards the opening of the inferior vena cava; this is the sulcus terminalis.
If we turn it around to look on the inside of the atrium, we can see a bulge. This muscular ridge corresponds to the sulcus terminalis on the outside and is known as the crista terminalis.
Crista Terminalis
The crista terminalis is a smooth muscular ridge that begins next to the opening of the superior vena cava and ends near the opening of the inferior vena cava.
Sinus of venae cavae (Sinus venarum)
Behind the crista terminalis lies a smooth area, known as the sinus of venae cavae. This is a smooth quadrangular area positioned between the openings of the superior and inferior venae cavae, where both venae cavae open into the right atrium.
The sinus of vena cava it’s where the superior and inferior vena cava open.
Opening of Superior Vena Cava
The opening at the top, situated superiorly, is known as the opening of the superior vena cava.
Opening of Inferior Vena Cava
Directly below it, there is another similar opening, known as the opening of the inferior vena cava.
Opening of Coronary Sinus
In front of these, positioned inferiorly, is the area where the coronary sinus opens, known as the opening of the coronary sinus.
Valve of Coronary Sinus (Thebesian Valve)
A closer look at the opening of the coronary sinus reveals it is guarded by a valve. This valve, presenting as a fold, is known as the valve of the coronary sinus or the Thebesian valve and is positioned in front and below the opening of the coronary sinus.
Valve of Inferior Vena Cava (Eustachian Valve)
The opening of the inferior vena cava is protected by a valve in front, referred to as the valve of the inferior vena cava or the Eustachian valve. In the developmental stages, blood passes from the left atrium in the right atrium via the foramen ovale, an opening situated on the interatrial septum, a muscular wall that divides the two atria. The main role of this valve is to channel blood flow through the opening.
Interatrial septum
The interatrial septum is a thin wall that separates the two atria. Looking at an anatomical model, we can observe that the interatrial septum is positioned somewhat obliquely, starting from the right and extending forward. This orientation is due to the heart’s position within the chest, as previously mentioned.
Fossa ovalis of right atrium
The opening mentioned earlier that is present in the developing heart, in the adult hart, normaly it is sealed and becomes fossa ovalis. Fossa ovalis of right atrium presents as an oval depression that is positioned on the lower part of the interatrial septum.
Limbus fossae ovalis
Examining the upper part of the fossa ovalis, we notice it is slightly raised; this area is known as the limbus of the fossa ovalis. Essentially, it marks the upper border of the fossa ovalis.
Pectinate muscles of right atrium
Returning to the crista terminalis, we look at the front of it and observe there are muscular bands extending over the wall of the right atrium. These elevated bands are known as the pectinate muscles of the right atrium. These muscles stretch over a part often referred to as the atrium proper.
Right auricle of heart
The pectinate muscles also extend upwards into an outpouching with a wide base and superior positioning. This outpouching is identified as the right auricle of the heart. Upon closer inspection from the outside, it’s evident that the right auricle is situated adjacent to the aorta.