Cardiac Cycle and Function Quiz

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Questions and Answers

What is the primary purpose of understanding the pressure-volume relationship in the cardiac cycle?

To analyze the effects of exercise on heart function

To measure blood pressure in systemic circulation

To describe the phases of the cardiac work loop (correct)

To estimate heart rate variability

Which parameter is a good estimate of preload in a normal heart?

Arterial blood pressure

Stroke volume

Cardiac output

Left ventricular end-diastolic pressure (correct)

How does an increase in arterial pressure typically affect cardiac workload?

It has no effect on cardiac output

It increases cardiac workload (correct)

It leads to a decrease in afterload

It decreases stroke volume significantly

What does the Frank-Starling mechanism primarily illustrate?

The increase in stroke volume with increased ventricular filling Signup and view all the answers

What happens to heart rate if the heart does not receive any neural impulses?

The heart rate decreases to cessation Signup and view all the answers

Which of the following defines cardiac contractility?

The intrinsic ability of the heart muscle to contract Signup and view all the answers

What is the effect of preload on stroke volume?

Increased preload increases stroke volume Signup and view all the answers

What is the significance of the tension/length relationship in the context of a pressure/volume loop?

It helps predict diastolic filling rates and output Signup and view all the answers

What occurs during isovolumic contraction?

The cardiac muscle generates energy using maximum oxygen consumption. Signup and view all the answers

What pressure does the aorta reach to ensure the opening of the aortic valve?

120 mmHg Signup and view all the answers

What is the primary factor enabling the forceful contraction of the cardiac muscle?

Maximum ATP production Signup and view all the answers

What phase follows the closure of the aortic valve?

Diastolic phase Signup and view all the answers

When does isovolumic relaxation occur?

After the aortic valve closes and before the mitral valve opens Signup and view all the answers

Which valves close at the end of the ejection phase?

Aortic and pulmonary valves Signup and view all the answers

What leads to the closure of the aortic valve?

Relaxation of the ventricular muscle Signup and view all the answers

What initiates the closure of the mitral valve?

Pressure increase in the left ventricle Signup and view all the answers

What is the end systolic volume referred to in the content?

50 ml Signup and view all the answers

Which valve is mentioned as closing first when the left ventricle contracts?

Mitral valve Signup and view all the answers

What percentage of blood does slow filling contribute after the rapid filling phase?

20% Signup and view all the answers

What happens to the blood during the contraction of the left ventricle?

It escapes through the aortic valve. Signup and view all the answers

What is the maximum filling volume reached before the contraction of the ventricle?

120 ml Signup and view all the answers

What occurs immediately after the left ventricle begins to contract?

The AV valve closes. Signup and view all the answers

What role does the rapid filling phase play in the heart's cycle?

It prepares the ventricles for blood ejection. Signup and view all the answers

What happens to the AV valve during a successful contraction of the ventricle?

It closes to prevent backflow. Signup and view all the answers

What is the effect of increasing preload on cardiac contraction?

It can lead to a more powerful cardiac contraction within limits. Signup and view all the answers

What does preload correspond to in the heart's functioning?

Volume at the end of diastole. Signup and view all the answers

What happens if the end diastolic volume exceeds 150 ml?

There is a sharp increase in pressure. Signup and view all the answers

How does afterload affect the heart's ability to contract?

Higher afterload results in increased vascular impedance. Signup and view all the answers

What is the main factor on which preload depends?

The volume of blood returning to the heart. Signup and view all the answers

What causes an increase in vascular resistance?

Increased arterial pressure. Signup and view all the answers

According to the Frank-Starling law, what is the relationship between muscle fiber stretching and contraction strength?

There is an optimal level of stretching for maximal contraction force. Signup and view all the answers

What is considered the normal maximum limit of end diastolic volume for effective cardiac contraction?

150-160 ml. Signup and view all the answers

What happens to preload when end diastolic volume is increased?

Preload increases. Signup and view all the answers

How does a higher preload affect stroke volume in a normal heart?

It leads to a higher stroke volume. Signup and view all the answers

What is the normal maximum limit for end diastolic volume in a healthy heart?

150 ml Signup and view all the answers

In athletes, what facilitates a decrease in vascular resistance during exercise?

The release of nitric oxide. Signup and view all the answers

What is the effect of increasing end diastolic volume on the force of cardiac muscle contraction?

It leads to an increase in contraction force. Signup and view all the answers

What happens to end systolic volume when stroke volume increases due to higher preload?

End systolic volume decreases. Signup and view all the answers

Why do athletes experience an increase in end diastolic volume during exercise?

Their heart chambers size increases. Signup and view all the answers

What role does endothelium-derived relaxing factor (EDRF) play after exercise in athletes?

It continues to promote vasodilation. Signup and view all the answers

What is the effect of increased stroke volume on the end-systolic volume (ESV)?

ESV decreases Signup and view all the answers

What does the Frank Starling mechanism allow the heart to do?

Adapt and pump out increased volumes of incoming blood Signup and view all the answers

When the ventricles are filled with an excessive amount of blood, what happens to the ability to contract?

It decreases because actin and myosin are too far apart Signup and view all the answers

What effect does the stretch of the right atrium have on the SA node?

It stimulates the SA node, increasing heart rate Signup and view all the answers

Which of the following is a factor influencing cardiac contractility?

Intrinsic cardiac regulation Signup and view all the answers

What happens to stroke volume when end-diastolic volume (EDV) increases in a healthy heart?

Stroke volume increases Signup and view all the answers

What is the relationship between ventricular filling and contraction force according to cardiac physiology?

Greater filling enhances contraction force Signup and view all the answers

What occurs simultaneously with increased venous return to the right atrium?

Stretch of the right atrium and stimulation of the SA node Signup and view all the answers

Study Notes

Pressure-Volume Relationship

Pressure and volume change during the cardiac cycle's phases, related to valve openings and closings
These changes are represented graphically as pressure-volume curves
The curves illustrate the periods of filling, ejection, isovolumic relaxation, and isovolumic contraction
The shape of the curves reveals the different pressures and volumes at each stage of the cardiac cycle

Cardiac Cycle

The cardiac cycle comprises a series of events that result in the pumping of blood.
The cycle is divided into phases such as filling, ejection, isovolumetric relaxation, and isovolumetric contraction.
The pressure and volume changes during each phase create the characteristic pressure-volume curve of the heart.

Preload

Preload is the tension in the ventricles at the onset of contraction.
It is related to end-diastolic volume, the volume of blood in the ventricles at the end of diastole.
An increase in preload increases the force of contraction and stroke volume.
Important factors of preload are end-diastolic volume (EDV) and venous return.

Afterload

Afterload refers to the resistance the heart must overcome to pump blood.
The pressure in the aorta (and pulmonary artery) is a major determinant of afterload.
Higher afterload reduces stroke volume.
Significant factors include hypertension and stenosis.

Frank-Starling Mechanism

This mechanism describes the intrinsic ability of the heart to adapt its contractile strength based on the end-diastolic volume.
The greater the EDV, the more stretched the cardiac muscle fibers.
This stronger stretch increases the force of contraction, leading to a more forceful ejection of blood.
The result is an increase in stroke volume.

Cardiac Contractility

Intrinsic factors regulate the volume of blood the heart pumps.
The heart instantaneously adjusts how much blood to pump based on the incoming volume.
Extrinsic controls: autonomic nervous system controls rate and strength of contraction.

Sympathetic Activity

Sympathetic innervation originates from upper thoracic segments of the sympathetic chain.
Increasing sympathetic stimulation increases heart rate, force of contraction, and conduction velocity.
Neurotransmitters (norepinephrine) act on β1-adrenergic receptors.

Parasympathetic Activity

Parasympathetic innervation to the heart primarily targets conduction and nodal tissues via the vagus nerve.
Parasympathetic stimulation slows the heart rate.
The neurotransmitter acetylcholine acts via muscarinic receptors (M2).

Learning Objectives

Students can describe the different phases of the cardiac cycle's work loop (pressure/volume relation).
They can define preload and identify parameters that estimate preload.
Students understand the effect of changes in preload and afterload on cardiac workload.
Students can explain how tension/length relationship is converted to a pressure/volume loop and relate it to filling rate and ventricular output.
They can describe the importance of Frank-Starling mechanism in cardiac function.
Definitions of cardiac contractility and how the Frank-Starling principle is different from contractility changes
Students understand how cardiac contractility and heart rate are influenced sympathetic and parasympathetic activity
Students identify what happens to the heart rate if it does not receive neural impulses.

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Description

Test your knowledge on the cardiac cycle, including the pressure-volume relationship and factors influencing cardiac contractility and preload. This quiz covers key concepts such as the Frank-Starling mechanism, isovolumic phases, and the significance of pressure during the cardiac cycle. Perfect for students of physiology or medicine.