Question

According to the Frank-Starling law of the heart, the strength of ventricular contraction is a. directly proportional to the end-diastolic volume. b. inversely proportional to the end-diastolic volume. c. independent of the end-diastolic volume. d. All of these are correct.

Short answer

The correct relationship between the strength of ventricular contraction and the end-diastolic volume according to the Frank-Starling law of the heart is: a. directly proportional to the end-diastolic volume.

Step-by-step solution

Introduce the Frank-Starling Law of the Heart

The Frank-Starling law of the heart is a physiological concept that states the stroke volume (amount of blood pumped by the left ventricle per beat) increases as the end-diastolic volume (the volume of blood in the left ventricle at the end of diastole, just before contraction) increases. In other words, the more blood that fills the heart during diastole, the stronger the subsequent contraction will be, and the more blood will be ejected from the heart.

Analyze the given options

Now that we understand the concept of the Frank-Starling law, let's analyze each of the given options: a. directly proportional to the end-diastolic volume: This option implies that as end-diastolic volume increases, the strength of ventricular contraction also increases. b. inversely proportional to the end-diastolic volume: This option means that if end-diastolic volume increases, the strength of ventricular contraction decreases, and vice versa. c. independent of the end-diastolic volume: This option suggests that the strength of ventricular contraction is not affected by changes in end-diastolic volume. d. All of these are correct: This option claims that all the above relationships are correct, which can't be true as they contradict each other.

Apply the concept to identify the correct option

Based on the Frank-Starling law, we know that the strength of ventricular contraction increases as the end-diastolic volume increases. Therefore, the correct relationship is: a. directly proportional to the end-diastolic volume. The other options contradict the concept of the Frank-Starling law, so they are incorrect.

Final answer

The correct relationship between the strength of ventricular contraction and the end-diastolic volume according to the Frank-Starling law of the heart is: a. directly proportional to the end-diastolic volume.

Key concepts

Ventricular Contraction

Ventricular contraction is a crucial process in the heart's functioning. It happens after the atria contract and fill the ventricles with blood. The ventricles, which are the lower chambers of the heart, then contract to pump blood out to the rest of the body.
This contraction is primarily facilitated by the heart muscle's ability to generate force. Several factors influence how strong this contraction is.

• The Frank-Starling mechanism states that the heart can automatically adjust the force of contraction based on the blood volume filling the heart.
• Neurotransmitters and hormones like adrenaline can also affect ventricular contraction strength.
• Blood pressure and heart rate are external factors that can impact the strength of contractions.

This process ensures that oxygen-rich blood returns to circulate throughout the body efficiently.

End-Diastolic Volume

End-diastolic volume (EDV) is the total amount of blood in the ventricles before they contract. It represents how much blood the heart receives from the body and lungs during diastole, the relaxed phase of the heartbeat.
Larger EDV means more blood stretches the heart muscle, preparing it for the contraction.

• The Frank-Starling law highlights that greater EDV increases the force of contraction, allowing the heart to pump more blood per heartbeat.
• Factors affecting EDV include the volume of returning blood to the heart and how long the ventricles have to fill.
• Healthy heart function requires a balance, as too much or too little EDV can cause strain or inefficiency.

Understanding EDV is essential for grasping how the heart adapts to the body's changing needs.

Stroke Volume

Stroke volume (SV) is the amount of blood pumped by the left ventricle with each heartbeat. It is a key measurement of heart efficiency and depends heavily on end-diastolic volume and ventricular contraction.

• The formula to calculate stroke volume is: \( SV = EDV - ESV \), where ESV is the end-systolic volume (the remaining blood in the ventricle after contraction).
• The Frank-Starling law suggests that with an increased EDV and optimal contraction, SV also rises.
• Changes in stroke volume can indicate heart health and adaptability. For example, lower SV could signal heart failure, while higher SV in athletes shows increased performance.

Stroke volume is an essential concept, as it links heart preload, contraction strength, and cardiac output.