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Sino-atrial node initiates the wave of c...

Sino-atrial node initiates the wave of contraction when

A

Only right atrium is full

B

Only left atrium is full

C

Both atria are full

D

Both ventricles are full

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Sino-atrial Node (SA Node)**: - The Sino-atrial node, commonly known as the SA node, is a small bundle of specialized cells located in the right atrium of the heart. It acts as the heart's natural pacemaker. 2. **Function of the SA Node**: - The primary function of the SA node is to generate electrical impulses that initiate the heartbeat. These impulses cause the atria (the upper chambers of the heart) to contract. 3. **Initiation of Contraction**: - The SA node generates an electrical impulse that spreads through the walls of both the right and left atria. This electrical activity leads to the contraction of the atria, pushing blood into the ventricles (the lower chambers of the heart). 4. **Condition for Initiation**: - The SA node initiates the wave of contraction when both atria are filled with blood. This ensures that the heart is ready to pump blood effectively into the ventricles. 5. **Correct Answer**: - Therefore, the correct answer to the question is that the Sino-atrial node initiates the wave of contraction when **both atria are full**.
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