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.
But your heart does not drive blood throughout your body in a circle, but in a more of a figure-8 pattern. The heart pumps blood along two pathways in your body, the pulmonary circuit and the systemic circuit. In the pulmonary circuit, the heart pumps blood to the lungs, then back to the heart. From this pathway, blood picks up oxygen and drops off carbon dioxide in the lungs. Put simply, blood is oxygenated in the lungs. In the systemic circuit, the longer of the two, the heart pumps oxygenated blood through the rest of your body. As the blood passes through organ after organ, tissue after tissue, blood drops off oxygen, and picks up carbon dioxide.