Question

Read the following statements and choose the correct option:

Statement $1$ : Atria receives blood from all parts of the body which subsequently flows to ventricles.

Statement $2$ : Action potential generated at sino-atrial node passes from atria to ventricles.

• A. Action mentioned in Statement 2 is dependent on action mentioned in Statement 1
• B. Action mentioned in Statements 1 and 2 are synchronous.
• C. Action mentioned in Statements 1 and 2 are independent of each other.
• D. Action mentioned in Statement 1 is dependent on action mentioned in Statement 2

Answer 1

The correct option is D Action mentioned in Statement 1 is dependent on action mentioned in Statement 2

SA node as pacemaker:

The cells of S.A (sinus node) node have the ability to generate the electrical impulse spontaneously. Thereby it sets the normal rhythm of a healthy heart, and also maintains the heart rate. The human heart normally beats 70-75 times per minute. Due to such functionality of auto excitation and setting up the rhythmic contractility, the SA node is referred to as the pacemaker of the heart.

Physiology of conduction:

$\bullet$ The electrical impulse is generated by the sinoatrial (SA) node.

$\bullet$ This impulse is spread through the right atrium and the left atrium and stimulates the atria to contract, pumping blood into the right and left ventricles, respectively.

$\bullet$ Then the electrical impulse spreads to the atrioventricular (AV) node located between the atria and the ventricles.

$\bullet$ From the AV node, it spreads into the bundle of His (specialized system of fibers) and the right and left bundle branches .

$\bullet$ These fibers transmit this impulse rapidly to all the areas of the right and left ventricles

$\bullet$ It stimulates them to contract in a coordinated manner.

$\bullet$ The blood is pumped from the right ventricle towards the lungs (for getting oxygenated), and from the left ventricle towards the body organs.

Explanation :

$\bullet$ Action potential generated at the SA node causes the ventricles to contract and the blood goes to the lungs from the right ventricle and into the aorta from the left ventricle.

$\bullet$ After emptying of the ventricles the blood enters the atrium.

Final answer

Action mentioned in Statement $1$ is dependent on action mentioned in Statement $2$ so the correct option is a.