The Cardiovascular System – The Atria

By: Alere Staff

The pump that ceaselessly works to circulate blood throughout the human body is the four chambered heart. The upper two chambers are known as the left and right atria and the lower two chambers as the left and right ventricles. The left and right sides of the heart are separated by a wall of muscle known as the septum but all four chambers are connected through valves.

Whereas the ventricles have the job of pushing blood out to all organs in the body, the role of the atria is to receive blood back into the heart. The walls of the atria are much thinner than the ventricular walls which facilitate the return of blood into the pump.

Large veins deliver deoxygenated blood from the entire body to the right atrium, which is then sent to the right ventricle and subsequently to the lungs to receive a fresh supply of oxygen. The left atrium receives the oxygen rich blood from the lungs and pushes it to the left ventricle for circulation to the entire system.

In the wall of the right atrium lies the sinoatrial node which is a group of pacemaker cells which create the electrical impulse that initiates contraction of the heart. The atria contract first as they pump blood to their corresponding ventricles. This creates the “lub” part of the “lub-dub sound”. The contraction of the ventricles immediately follows and creates the “dub” part of the sound.

The atria play a very important role in completing the ongoing circulation cycle as they allow and receive blood back to the heart to start the sequence of nourishing our bodies over and over again our whole lifetime.

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  1. National Geographic Society. Heart. 2015.
  2. Bailey, Regina. Atria of the Heart. About Education. Retrieved March 20, 2015 from website:
  3. Wikipedia. Atrium (heart). Retrieved March 20, 2015 from website: