Cardiac Physiology: Heart Conduction System

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Questions and Answers

What mechanism does the baroreceptor reflex primarily utilize for short-term blood pressure control?

Reduction of heart rate (correct)

Control of cardiac output and total peripheral resistance (correct)

Increased renal blood flow

Enhanced blood viscosity

What characterizes primary hypertension?

It occurs due to other underlying factors.

It has a known physiological cause.

It is always accompanied by kidney dysfunction.

The cause is not known. (correct)

Which factor is directly linked to secondary hypertension?

Dietary sodium intake

Lifestyle choices such as exercise

Another underlying medical condition (correct)

Genetic predisposition

What is the blood pressure range that defines hypotension?

BP < 100/60 mmHg Signup and view all the answers

Which of the following conditions can result from heart failure?

Renal failure due to under perfusion Signup and view all the answers

What happens to stroke volume when there is increased end-diastolic volume (EDV)?

It increases due to enhanced myocardial stretch. Signup and view all the answers

Which statement about Frank-Starling's law is true?

Higher initial length of cardiac muscle fibers correlates with greater contraction force. Signup and view all the answers

What role does the autonomic nervous system play in initiating the heartbeat?

It modulates the heartbeat frequency after initiation by the SA node. Signup and view all the answers

How does sympathetic nervous system activity affect cardiac output?

It increases heart rate and stroke volume. Signup and view all the answers

What is the effect of parasympathetic activity on the atria?

It decreases heart rate and stroke volume for atrial contractions. Signup and view all the answers

What effect does sympathetic stimulation have on arterioles?

Decreases diameter, resulting in vasoconstriction. Signup and view all the answers

Which statement accurately describes the relationship between venous return and stroke volume?

Greater venous return enhances stroke volume through myocardial stretch. Signup and view all the answers

Which of the following best describes the function of the SA node?

It spontaneously generates electrical impulses to initiate heartbeats. Signup and view all the answers

What is the formula to calculate Cardiac Output (CO)?

CO = HR x SV Signup and view all the answers

Which factor is NOT associated with increasing Heart Rate (HR)?

Parasympathetic stimulation on SA node Signup and view all the answers

According to Frank-Starling's law, what occurs with increased venous return to the heart?

Increased stroke volume Signup and view all the answers

Which statement accurately describes the control of Stroke Volume (SV)?

It can be influenced by both intrinsic and extrinsic factors. Signup and view all the answers

Which of the following conditions is likely to decrease Heart Rate (HR)?

Advanced age Signup and view all the answers

What is primarily responsible for the intrinsic control of Stroke Volume?

Venous return Signup and view all the answers

When is parasympathetic discharge dominant in controlling Heart Rate (HR)?

During rest Signup and view all the answers

What is the expected Cardiac Output (CO) when Heart Rate (HR) is 70 BPM and Stroke Volume (SV) is 70 ml/beat?

4900 ml/min Signup and view all the answers

What role does the SA node play in the cardiac conduction system?

It generates the fastest rate of action potentials. Signup and view all the answers

Which component of the cardiac conduction system has the slowest conduction velocity?

AV node Signup and view all the answers

What is the primary purpose of AV nodal delay?

To allow complete filling of the ventricles. Signup and view all the answers

What does the P wave in an ECG tracing represent?

Atrial Depolarization Signup and view all the answers

Which structure is responsible for rapid and simultaneous excitation of the ventricles?

Purkinje fibers Signup and view all the answers

What is the relationship between End Diastolic Volume (EDV) and End Systolic Volume (ESV) in calculating Stroke Volume (SV)?

SV = EDV - ESV Signup and view all the answers

How many action potentials does the SA node typically discharge per minute?

70-80 Signup and view all the answers

Which of the following statements about Heart Rate (HR) is true?

HR is typically higher in sedentary individuals than in athletes. Signup and view all the answers

Which of the following statements is true regarding the electrocardiogram (ECG)?

It records the heart’s electrical activity from electrodes placed on the skin. Signup and view all the answers

What distinguishes the AV node in terms of its function in the heart?

It functions as a relay point for electrical impulses between the atria and ventricles. Signup and view all the answers

What does tachycardia indicate regarding heart rate?

A heart rate greater than 100 BPM Signup and view all the answers

Which structure has a conduction velocity of 4.0 m/Sec?

Purkinje fibers Signup and view all the answers

Which component of the ECG tracing signifies ventricular depolarization?

QRS complex Signup and view all the answers

What is the average stroke volume (SV) for a healthy adult?

70 ml/beat Signup and view all the answers

Which of the following conditions could lead to bradycardia?

Parasympathetic stimulation Signup and view all the answers

What characterizes cardiac output (CO)?

It is the amount of blood pumped out of each ventricle in one heart-beat. Signup and view all the answers

Study Notes

Heart - Functional Syncytium

Heart is a functional syncytium due to the presence of gap junctions and the fast-conducting system between atria & ventricles.

Origin and Spread of Cardiac Impulse

The SA node is the pacemaker of the heart.

Pacemaker Activity

SA node has the fastest rate of action potential discharge (70-80/min).
AV node has a slower discharge rate (40-60/min).
Bundle of His and Purkinje fibers have even slower discharge rates (20-40/min).

Conduction Velocity

Purkinje fibers have the fastest conduction velocity (4.0 m/s).
Bundle of His has a moderate conduction velocity (0.3 - 1 m/s).
Nodal fibers have the slowest conduction velocity (0.02 - 0.1 m/s).

AV Nodal Delay

The impulse is delayed in the AV node for 0.1 seconds, allowing the atria to contract completely before the impulse reaches the ventricles.
The delay ensures that the ventricles fill completely before contraction.

Purkinje Fibers

Purkinje fibers are the fastest conducting cells in the heart.
This ensures rapid and simultaneous excitation of both ventricles.

ECG (Electrocardiogram)

ECG records the electrical activity of the heart.
The P wave represents atrial depolarization.
The QRS complex represents ventricular depolarization.
The T wave represents ventricular repolarization.

Cardiac Rhythm

An abnormal heart rhythm is known as arrhythmia.

Cardiac Output (CO)

CO is the volume of blood pumped by each ventricle per minute.
CO = HR x SV (Heart Rate x Stroke Volume)

Stroke Volume (SV)

SV is the volume of blood ejected from the ventricle per heartbeat.
SV = EDV (End Diastolic Volume) - ESV (End Systolic Volume)

Factors Regulating Heart Rate

Factors Increasing Heart Rate:
- Sympathetic stimulation
- Epinephrine release
- Increased body temperature
- Anxiety
- Young children
Factors Decreasing Heart Rate:
- Parasympathetic stimulation
- Decreased body temperature
- Advanced age
- Rest (parasympathetic dominance)

Factors Regulating Stroke Volume

Intrinsic Control (Venous Return): Increased venous return leads to increased stroke volume (Frank-Starling law).
Extrinsic Control (Autonomic Nervous System): Sympathetic stimulation increases the force of contraction.

Frank-Starling's Law of the Heart

Increased venous return to the heart stretches the heart muscle fibers.
Increased stretch leads to increased force of contraction.
This results in an increased stroke volume.

Autonomic Regulation

The autonomic nervous system does not initiate the heartbeat.
The SA node does this spontaneously but is modulated by the autonomic nervous system.

Sympathetic Regulation

Increases heart rate and stroke volume.
Increases cardiac output.
Causes vasoconstriction.

Parasympathetic Regulation

Decreases heart rate.
Decreases stroke volume.
Decreases cardiac output.

Blood Pressure Control

Short-term (within seconds): Baroreceptor reflex (adjusts CO and TPR).
Long-term (minutes-days): Renal compensation (adjusts urine output).

Hypertension

High blood pressure (BP > 140/90 mmHg).
Primary (Essential) Hypertension: Cause unknown.
Secondary Hypertension: Caused by another factor.

Hypotension

Low blood pressure (BP < 100/60 mmHg).

Heart Failure

Inability of the heart to supply adequate blood flow to tissues and organs.
Causes fatigue, shortness of breath, and decreased exercise capacity.
Can lead to organ dysfunction.

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Description

Explore the intricate functioning of the heart's conduction system in this quiz. Learn about the role of the SA node, AV node, and Purkinje fibers in maintaining heart rhythm and conduction velocity. This quiz covers essential concepts related to functional syncytium and pacemaker activity.