Question

Read the statements and select the option which best describes the process that occurs during systematic circulation.
(i) The left atrium receives the oxygenated blood through the pulmonary veins. The left ventricle pumps the blood through the aorta to various parts and the de-oxygenated blood reaches right atrium.
(ii) The left atrium receives the oxygenated blood through pulmonary veins and pumps the blood through the aorta to various parts and the de-oxygenated blood reaches the right atrium.
(iii) The left atrium receives de-oxygenated blood and pumps into left ventricles which in turn pumps into pulmonary artery for oxygenation.
(iv) The right atrium receives the de-oxygenated blood and pumps into pulmonary artery for oxygenation.

• A. (i) and (iii) are correct
• B. (ii) is correct
• C. (iii) and (iv) is correct
• D. (iv) is correct

Answer 1

The correct option is D (iv) is correct

Blood is pumped by the right side of the heart to the lungs, where it passes through a capillary bed and picks up vital supplies of oxygen from the air in the lungs. This newly oxygenated blood collects in the pulmonary veins and travels to the left atrium of the heart. The left atrium acts as a collecting chamber for blood and allows it to pass into the larger and more muscular left ventricle. Stimulatory signals from the sinoatrial (SA) node in the right atrium act as a pacemaker and trigger the coordinated contraction of the myocardium of the atria, known as atrial systole. Atrial systole results in the active pumping of blood from the left atrium into the left ventricle to fill the ventricle completely. The left ventricle contracts a few milliseconds after the left atrium, forcing the bicuspid valve to close and pumping blood into the aorta and onwards towards the body’s organ systems. While the ventricles are contracting, the left atrium relaxes to allow more blood from the lungs to refill its chamber and prepare for the next cardiac cycle. Deoxygenated blood enters the right atrium through three major veins the superior and inferior vena cava and the coronary sinus. The right atrium not only receives blood passively from the veins, but also actively pumps blood into the right ventricle. During the relaxation phase of the cardiac cycle, cardiac muscle in all of the chambers of the heart relaxes, allowing the chambers to increase their volume. Blood returning from the veins flows into the right atrium and through the tricuspid valve to the right ventricle. About 70% of the ventricular filling occurs during this phase. The right atrium next goes into systole, or contraction, to pump blood actively into the right ventricle and completely fill it. The right ventricle next goes into systole to pump blood to the lungs. The closing of the tricuspid valve blocks blood attempting to flow back to the right atrium from the right ventricle, so that blood is efficiently pumped in one direction only.

Therefore, the correct answer is option D.