Also see user session. In telecommunication, a session is a series of interactions between two communication end points that occur during the span of a single connection.
The path of blood through the heart begins with the right atrium receiving blood, which has circulated through most of the body. This blood is relatively low in oxygen because most of it has already been delivered to different organs and tissues.
After the blood receives oxygen, it returns to the left side of the heart, the left atrium. After collecting in the left atrium, it is pumped into the left ventricle, and from there it is pumped into the aorta, the largest blood vessel in the body. From the aorta, blood courses throughout the body through its arteries. For blood to go in only one direction, forward, it must pass through the heart valves, which function as one-way doors, opening and shutting with each beat of the heart. Just as there are four chambers to the heart, there are four heart valves.