Questions & Answers

Differentiate between lub and dup sound.

169.2k+ views
Hint: Normal heart sounds can be characterized by a ‘lub’ ‘dub’ that occurs with a heartbeat. The first heart sound (lub) occurs when the atrioventricular (AV) valves close and the second heart sound (dub) is heard when the semilunar valves close.

Complete answer: The circulation of blood begins with the contraction of the atria. At this time, the ventricle is relaxing and empty, so the blood from the atria passes to the ventricle easily. When blood reaches the ventricle, ventricles contract and atria relax. On contraction of the ventricle, the blood passes from ventricles to the lungs for oxygenation. The blood tends to return to the ventricles under pressure, but the two atrioventricular valves (bicuspid and tricuspid valve) prevents it from flowing back. The valve's flaps thus, closing the passage. This closing of valves produces the ‘lub sound’, i.e. at the beginning of the ventricular systole. Then the blood reaches lungs, gets oxygenated and returns to the right atria with the help of the pulmonary artery. The atria contract, which makes the blood flow to ventricles. The blood then gets ready to move into the aorta for distribution. When it moves to the aorta, it tends to return. To prevent this the semilunar valve gets closed, thus producing the ‘dub sound’. So, the lub sound is produced when atrioventricular valves are closed, and the dub sound is produced when the semilunar valves are closed. Lub is the first sound which is fairly loud, and dub sound is the second sound which is softer.

Note: There may be a third heart sound also called a protodiastolic gallop. The third heart sound is benign in youth, some trained athletes and sometimes in pregnancy but if it reemerges later in life, it may signal cardiac problems, such as a failing left ventricle as in dilated congestive heart failure.