Heart Anatomy and Cardiac Cycle

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Questions and Answers

What does each hill and valley in the M-mode capture of the heart represent?

Atrial and ventricular contraction phases

Diastolic filling periods

Systole and diastole (correct)

End-systolic and end-diastolic volumes

Which condition is characterized by concentric hypertrophy?

HFrEF

HFpEF (correct)

Healthy heart

Non-hypertensive heart disease

In the context of heart measurements, what is typically measured using M-mode ultrasound?

Cardiac output

Heart rate variability

Wall thickness and chamber size (correct)

Blood pressure dynamics

What is a common heart rate range for a mouse heart during high-frequency ultrasound examination?

300-500 bpm Signup and view all the answers

How is HFrEF primarily differentiated from HFpEF?

By wall thickness-to-chamber radius ratio Signup and view all the answers

What is the primary function of the heart?

Oxygenate and deliver blood throughout the body Signup and view all the answers

During which phase of the cardiac cycle does the heart fill with blood?

Diastole Signup and view all the answers

Which chamber of the heart has the thickest walls?

Left ventricle Signup and view all the answers

What characterizes heart failure with preserved ejection fraction (HFpEF)?

Diastolic dysfunction Signup and view all the answers

Which statement about systole is correct?

It occurs when the heart muscles contract to push blood out. Signup and view all the answers

What impact does estrogen deficiency have on heart failure in women?

Contributes to HFpEF development Signup and view all the answers

What role does the left ventricle play in the cardiac cycle?

It generates pressure to push blood into the aorta. Signup and view all the answers

What is the effect of diastolic dysfunction on the heart?

Reduces the ability of the heart to relax and fill. Signup and view all the answers

What measurement quantifies the heart's function by considering the volume of blood in the left ventricle at the end of diastole and end of systole?

Ejection fraction Signup and view all the answers

In HFpEF, what happens to the stroke volume despite preserved ejection fraction?

It decreases due to lower end-diastolic volume. Signup and view all the answers

How is cardiac output calculated?

SV x HR Signup and view all the answers

What characteristic describes the left ventricle in the context of diastolic dysfunction?

Increased stiffness Signup and view all the answers

What occurs to the preload in the context of heart failure with preserved ejection fraction (HFpEF)?

It decreases. Signup and view all the answers

Which mode is used to assess diastolic function by detecting the movement of red blood cells?

Pulse wave mode Signup and view all the answers

In HFrEF, what primarily decreases the stroke volume?

Decreased contractility Signup and view all the answers

What is the impact of increased left ventricular stiffness in relation to diastolic dysfunction?

It impairs relaxation. Signup and view all the answers

What is the primary function of the SA node in the heart?

It is the primary pacemaker setting the heart rate Signup and view all the answers

Which factor does NOT contribute to an increase in cardiac output?

Decreased heart rate Signup and view all the answers

Which term describes the heart's ability to increase blood output during high demand situations?

Cardiac reserve Signup and view all the answers

Increased SERCA-mediated calcium uptake results in which of the following?

Increased calcium stores in the sarcoplasmic reticulum Signup and view all the answers

What does the E/A ratio measure?

Atrial kick and ventricular filling dynamics Signup and view all the answers

What action occurs during isovolumetric contraction?

The ventricles contract without changing volume Signup and view all the answers

Which of the following best describes phospholamban's role in cardiac muscle?

Inhibits SERCA and decreases calcium uptake Signup and view all the answers

Which equation correctly represents cardiac output?

CO = Stroke volume x Heart rate Signup and view all the answers

What is the role of PKA in the fight or flight response?

It phosphorylates phospholamban at Ser16. Signup and view all the answers

How does an increase in preload affect stroke volume?

It increases myofilament overlap and enhances contractions. Signup and view all the answers

What would be the effect of activating calmodulin dependent kinase II (CaMKII)?

Phosphorylation of phospholamban at Thr17. Signup and view all the answers

Which mechanism primarily increases diastolic filling in the heart?

Increase in SERCA function. Signup and view all the answers

What effect does ↑ SERCA calcium uptake have on future contractions?

It facilitates a greater calcium release during contractions. Signup and view all the answers

What happens to the pressure gradient as left ventricular volume increases?

Left atrial pressure increases relative to left ventricular pressure. Signup and view all the answers

Which statement best describes the length-tension relationship in myofilaments?

Maximum force is produced with optimal myofilament overlap. Signup and view all the answers

What is the primary effect of norepinephrine binding to its G-protein receptor?

It promotes protein kinase A (PKA) activation. Signup and view all the answers

Study Notes

Heart Function

The heart's main role is to oxygenate blood by taking deoxygenated blood from the body and pumping it to the lungs to be oxygenated.
The heart also delivers oxygenated blood to the rest of the body.
Each chamber of the heart has muscular walls.
The left ventricle has the thickest walls and is responsible for generating enough pressure to pump blood throughout the body.

Diastole

Diastole is the relaxation phase of the cardiac cycle, during which the heart fills passively with blood.
Diastolic dysfunction in the left ventricle can affect how much blood is ejected into the body.
Most filling occurs passively during diastole, with an atrial kick (atrial systole) contributing at the end of atrial diastole.

Systole

Systole is the contraction phase of the cardiac cycle, during which the heart muscle contracts, pushing blood to the next chamber or the body.
The left ventricle generates enough pressure to push blood out to the aorta and the rest of the body.

Cardiac Output

Cardiac output is a measure of the heart's ability to pump blood out to the body.
Cardiac output is calculated as Stroke Volume x Heart Rate.
Stroke Volume is the amount of blood pumped out of the left ventricle in one beat, measured as End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
Heart Rate is the number of beats per minute.

Cardiac Reserve

Cardiac reserve represents the heart's ability to increase its output to meet demands.
It is achieved by increasing both stroke volume and heart rate.
This involves the "fight or flight" response, triggered by the release of epinephrine and norepinephrine.

Increasing Stroke Volume

Increased stroke volume is achieved through increased calcium release, which improves cardiac contractility.
This process involves the following key players:
- SERCA (Sarcoplasmic Endoplasmic Reticulum Calcium ATPase): A pump that transports calcium back into the sarcoplasmic reticulum (SR).
- DHPR (Dihydropyridine Receptor): Involved in calcium influx into the cell.
- RyR (Ryanodine Receptor): Responsible for calcium release from the SR.
Increased SERCA activity allows for increased calcium storage in the SR, leading to greater releasable calcium for muscle contraction.

Phospholamban

Phospholamban is a protein inhibitor of SERCA, highly expressed in cardiac muscle, particularly in the left ventricle.
It physically interacts with SERCA, preventing calcium binding and reducing its affinity for calcium.

Epinephrine/Norepinephrine and Cardiac Reserve

Norepinephrine binds to its G-protein receptor, activating Protein Kinase A (PKA).
PKA phosphorylates phospholamban at Ser16, reducing its inhibitory effect on SERCA, leading to increased calcium uptake.
PKA also phosphorylates DHPR and RyR, and activates CaMKII which phosphorylates PLN at Thr17.
These phosphorylation events collectively increase calcium in the cytosol, leading to more active muscle contraction.

Increased SERCA function and Diastolic Filling

Enhanced SERCA function leads to increased calcium uptake, promoting muscle relaxation and allowing for greater passive filling (increase in E wave).
Increased calcium uptake also contributes to increased "preload," the amount of blood in the ventricles, ultimately increasing stroke volume.

Preload and Cardiac Contractility

Increased preload stretches the myofilaments (myosin and actin).
Increased myofilament overlap results in increased crossbridge formation and decreased space between myosin and actin, leading to greater force production.

Measuring Left Ventricular Function with Ultrasound

High-frequency ultrasound can capture the heartbeat in short-axis view and M-mode (motion mode).
This allows for measurement of left ventricle (LV) structure:
- Wall thickness
- Chamber size
- Internal diameters
- End-diastolic volume (EDV)
- End-systolic volume (ESV)
- Stroke volume (EDV - ESV)
- Ejection Fraction (EDV - ESV/EDV * 100)
- Fractional Shortening (LVIDd - LVIDs/LVIDd * 100)

Heart Failure with Preserved Ejection Fraction (HFpEF)

HFpEF is commonly characterized by concentric hypertrophy, where wall thickness increases relative to chamber size.
Ejection Fraction (EF) is preserved (> 50%).
Stroke Volume is decreased due to smaller chamber volume despite preserved contractility.
Diastolic dysfunction is present, meaning impaired relaxation and increased stiffness of the ventricle.

Heart Failure with Reduced Ejection Fraction (HFrEF)

HFrEF is typically associated with eccentric hypertrophy, where chamber size increases without an accompanying increase in wall thickness.
Ejection Fraction is decreased (< 50%).
Decreased contractility reduces stroke volume.

Diastolic Dysfunction

Diastolic dysfunction is characterized by impaired left ventricular relaxation and increased stiffness, reducing the ventricle's ability to fill passively with blood.
This can be assessed using Pulse Wave (PW) mode ultrasound.
PW mode sends sound pulses that bounce off moving red blood cells, providing information about ventricular relaxation and compliance.

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Description

This quiz covers the essential functions of the heart, including the processes of diastole and systole. Understand how the heart oxygenates blood and the significance of each phase in the cardiac cycle. Test your knowledge about the heart's structure and its vital role in circulation.