Question

SA node is called the pace maker of the heart. Why? (a) It can change contractile activity generated by AV node. (b) It delays the transmission of impulse between the atria and ventricles. (c) It gets stimulated when it receives neural signal. (d) It initiates and maintains the rhythmic contractile activity of heart.

Short answer

The SA node is called the pacemaker of the heart because it initiates and maintains the rhythmic contractile activity of the heart (Option d).

Step-by-step solution

Understand the Choices

Evaluate each choice provided. (a) involves the role of the SA node in changing contractile activity generated by AV node. (b) mentions a delay in the transmission of impulse, which is the function of AV node, not the SA node. (c) refers to the SA node getting stimulated through a neural signal. (d) states that the SA node initiates and maintains the rhythmic contractile activity of the heart.

Highlight the SA Node’s Role

Focus on the roles that directly relate to the SA node being called the pacemaker of the heart. The SA node is responsible for initiating and maintaining the rhythmic contractile activity within the heart. This means option (d) describes the key role of why the SA node is called the pacemaker.

Discard the Irrelevant Choices

Discard the choices that do not directly explain why the SA node is called the pacemaker. In this context, choices (a), (b), and (c) could be eliminated. These choices describe functions that either pertain to the AV node (choice (b)) or do not fully explain why the SA node is labelled as the pacemaker (choices (a) and (c)).

Key concepts

Pacemaker of the Heart

The SA node, or sinoatrial node, is a small cluster of specialized cells located in the right atrium of the heart. It is often termed the "pacemaker of the heart" due to its unique ability to set the pace or the rhythm with which the heart beats. This small but mighty node is responsible for initiating each heartbeat, ensuring that the heart contracts in a coordinated and rhythmic manner.

Unlike other cardiac cells, the SA node cells can depolarize spontaneously. This means they don't need external influence to start an electrical impulse. This "automaticity" allows the SA node to initiate the electrical signals that cause heart muscle contractions and effectively sets the timing for these contractions.

Through its constant activity, the SA node determines the heart rate depending on the body's needs—be it rest, exercise, or stress. It adapts the heart rate, ensuring efficient blood circulation throughout the body. Therefore, it is an indispensable component in maintaining optimal cardiac rhythm and overall cardiovascular health.

Heart Rhythmic Contractile Activity

The concept of rhythmic contractile activity is central to understanding how our heart functions on a daily basis. This rhythmic activity refers to the consistent and orderly contractions of the heart muscle, facilitated by the cardiac conduction system, which coordinates each heartbeat.

The process starts at the SA node, which generates electrical impulses that lead to atrial contraction. These impulses then travel to the AV node and through the heart's conduction pathways, reaching the ventricles and causing them to contract. As a result, blood is effectively pumped throughout the body.

This coordinated sequence - atrial contraction followed by ventricular contraction - ensures that the heart works efficiently and maintains a consistent blood flow. The consistent rhythmic nature of these contractions is what enables the heart to pump blood without fatigue, sustaining life by supplying oxygen and nutrients to tissues while removing waste products.

AV Node Function

The atrioventricular node, or AV node, plays a critical role in the cardiac conduction system. It acts as a gatekeeper that regulates the transmission of electrical impulses from the atria to the ventricles.

One of its primary functions is to introduce a slight delay in the impulse transmission. This delay is crucial because it allows the atria to fully contract and complete the process of sending blood into the ventricles before they contract. This ensures that the ventricles fill with an adequate volume of blood, optimizing cardiac output.

In addition to this delay, the AV node can alter the heart rate under certain circumstances, such as during high physical demand or stress. It works in tandem with the SA node and other components of the conduction system to ensure the heart beats in a coordinated rhythm, adapting to the body’s varying demands throughout different activities and states of rest.