Atrium anatomy: Encyclopedia - Atrium anatomy

Atrium (anatomy)

In anatomy, the atrium (plural: atria) is the blood collection chamber of a heart. It has a thin-walled structure that allows blood to return to the heart. There is at least one atrium in an animal with a closed circulatory system. In fish, the circulatory system is very simple: a two-chambered heart including one atrium and one ventricle. In vertebrate groups that evolved later, the circulatory system is much more complicated. Their circulatory systems are divided into two types: a three-chambered heart, with two atria and one ventricle, or a four-chambered heart, with two atria and two ventricles. The atrium's function in the circulatory system includes receiving blood as it returns to the heart to complete a circulating cycle, whereas the ventricle's function is to pump blood out of the heart to start a new cycle.

Humans have a four chambered heart.

The right atrium receives deoxygenated blood from the superior vena cava and inferior vena cava. The left atrium receives oxygenated blood from the left and right pulmonary veins.

The atria do not have valves at their inlets. As a result, a venous pulsation is normal can be detected in the jugular vein (see: jugular venous pressure).

Internally, there is the rough musculae pectinati, crista terminalis which acts as a boundary inside the atrium and the smooth walled part derived from the sinus venosus. There is also a fossa ovalis in the interatrial septum which was used in the fetal period as a means of bypassing the lungs.

Adapted from the Wikipedia article "Atrium anatomy", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki