The right atrium lies anterior to the left atrium, and the right ventricle lies anterior to the left ventricle. The part of the atrium posterior to the ridge is smooth walled, whereas the interior of the auricle is roughened by bundles of muscle fibers, the musculi pectinati.
The right atrium consists of a main cavity and a small out pouching, the auricle.
The role of the right atrium and ventricle is to collect oxygen-poor blood from the body and pump it to the lungs. The role of the left atrium and ventricle is to collect oxygen-rich blood from the lungs and pump it throughout the body.
Within each side, the atrium is a site for the collection of blood, before pumping it to the ventricle.
Right atrium is larger than the left atrium but has a thinners wall and its sinus venarum between two vena cavae is separated from the atrium proper by the crista terminalis. Right atrium has at right atrial pressure that is normally slightly lower than left atrial pressure.
Left atrium is smaller and has thicker walls than the right atrium, but its wall are smooth, except for a few pectinate muscles in the auricle. The left atrium is situated behind the right atrium an forms the greater part of the base or the posterior surface of the heart.
Atrium of the heart
