Video Transcript
Which of the following is correct about the contractions of the heart? (A) The left ventricle contracts before the right, so the systemic circulation occurs before the pulmonary circulation. (B) The right ventricle contracts before the left, so the pulmonary circulation occurs before the systemic circulation. Or (C) the left and right ventricles contract at the same time, so pulmonary and systemic circulations happen simultaneously.
The question asks us about contractions of the heart muscles. So let’s begin by reviewing the basic structure of the heart and then look at the process of its contractions. You may remember that the heart is divided into four chambers: two upper chambers called atria, or singular atrium, and two lower chambers called ventricles.
There are two major circulatory pathways that make up what’s called a double circulation system. The pulmonary circulation pathway involves the transport of blood between the heart and the lungs, while the systemic circulation pathway involves the transport of blood between the heart and the other organs and tissues. These two circulatory pathways occur simultaneously, which means that deoxygenated blood arriving from the body’s organs and tissues arrives at the right atrium at the same time that oxygenated blood from the lungs arrives at the left atrium. The walls of the atria then contract, pumping the blood through the open valves into the right and left ventricles. The right and left ventricles then contract, pulling the valves into a closed position and pumping oxygenated blood to the body’s organs and tissues and deoxygenated blood to the lungs for oxygenation.
We can see in the diagram that the right and left ventricles are contracting at the same time. So the correct answer is (C). The left and right ventricles contract at the same time, so pulmonary and systemic circulations happen simultaneously.
