Right Atrium — External Features and Position
Position
The right atrium is the right upper chamber of the heart. It is situated behind and to the right of the right ventricle. It receives deoxygenated venous blood from the whole body and pumps it to the right ventricle through the right atrioventricular (tricuspid) orifice.
Contributions to Cardiac Anatomy
| Feature | Right Atrium Contribution |
|---|---|
| Right border of heart | Entirely — from SVC above to IVC below |
| Upper border | Partly (mainly left atrium) |
| Sternocostal (anterior) surface | Partly |
| Base of heart (posterior surface) | Small part (right 1/3rd; left atrium forms 2/3rd) |
Shape and Parts
- Shape: Quadrilateral, elongated vertically
- Two parts:
- Main cavity (body of right atrium)
- Right auricle (auricular appendage)
Right Auricle
- The upper end of the right atrium is prolonged to the left as the right auricle
- The auricle overlaps the root of the ascending aorta completely and the infundibulum of the right ventricle partly
- Margins of the auricle are notched
- Interior is sponge-like (reticular network of musculi pectinati) — this prevents free flow of blood and predisposes to thrombus formation
Sulcus Terminalis
A shallow vertical groove on the external surface of the right atrium:
- Extends along the right border between the openings of the SVC (above) and IVC (below)
- The upper part of the sulcus terminalis contains the sinoatrial (SA) node — the pacemaker of the heart
- Internally corresponds to the crista terminalis
Right Atrioventricular Groove (Coronary Sulcus — Right Part)
- Separates the right atrium from the right ventricle externally
- More or less vertical
- Lodges: right coronary artery and small cardiac vein