Explain why ventricular contraction[systole] and the lub sound occur immediately after the QRS complex.?
We don't have a tutor who specializes in this subject. Sorry.
Please make good use of https://www.khanacademy.org/ -- Click on Courses at the top left and choose what you need.
Ventricular contraction, also known as systole, and the "lub" sound occur immediately after the QRS complex for a specific reason. To understand why, we need to start by understanding the electrical and mechanical events that occur during a cardiac cycle.
During the cardiac cycle, the heart undergoes a series of events that result in the pumping of blood. These events can be divided into two phases: diastole and systole.
During diastole, the heart is relaxed, and the chambers fill with blood. This includes the ventricles, which are the main pumping chambers of the heart. As the heart fills with blood, the pressure inside the ventricles increases.
The next phase, known as systole, involves the contraction of the ventricles to pump blood out of the heart. The electrical activity responsible for initiating ventricular contraction is represented by the QRS complex on an electrocardiogram (ECG).
The QRS complex indicates the depolarization (contraction) of the ventricles, which leads to their contraction. This ventricular contraction increases the pressure inside the ventricles and causes the blood to be forced out of the heart into the arteries.
Now, let's talk about the "lub" sound, also known as the first heart sound or S1. This sound is produced by the closure of the mitral and tricuspid valves, known as the atrioventricular valves. The closure of these valves occurs during systole, specifically during the isovolumetric contraction phase.
When the ventricles contract, the pressure inside the ventricles rises rapidly. As the pressure exceeds the pressure in the atria, the mitral and tricuspid valves close, preventing the backflow of blood into the atria. This closure produces the "lub" sound.
To summarize, the ventricular contraction (systole) occurs immediately after the QRS complex on an ECG due to the depolarization of the ventricles. This contraction increases the pressure inside the ventricles and leads to the closure of the atrioventricular valves, causing the "lub" sound.