Cardiovascular System - Packet

Are the ventricles of the heart larger during systole or diastole?

Diastole

Why is the QRS complex larger than the P wave?

Ventricles are bigger, sum of activity

Place the events of a cardiac cycle in order.

1. Atrial diastole + repolarization 2. Atria fill with blood (ventricles also filling w/blood) 3. Atrial syncytium depolarizes/depolarization at AV node/ Ventricles become filled with blood 4. Cardiac impulse travels down the AV bundle 5. Atrial diastole + repolarization/ cardiac impulse travels down the bundle branches 6. Ventricular syncytium depolarized 7. Ventricular systole/ventricles empty 8. Cardiac impulse travels along Purkinje fibers 9. Ventricular diastole (and repolarization)

Ventricular fibrillation is the uncoordinated contraction of cardiac myocytes. Explain why "shocking" the heart can correct this problem.

An external electrical signal simulates the healthy heart's electrical signal and induces contraction, allowing the heart to resume normal contraction rhythm

What electrical event is taking place in the heart when the p wave is being recorded on the ECG?

Atrial depolarization

Myocytes (cardiac muscle cells) connected to one another by gap junctions, allowing ions to diffuse from one cell into adjacent cells. If a cardiac myocyte is brought to threshold (depolarizes), does it affect the cells around it? how so?

Ions can diffuse from that cell into nearby cells, so action potentials can easily travel from cell to cell

Atrial fibrillation is the rapid uncoordinated contraction of the atrial myocardium. Why is it not considered life-threatening?

Irregular signals in atria cause atria to beat irregularly but would not cause an abnormal heartbeat (ventricles larger, impact heart beat more)

Since all the myocytes in the atria are contracting (almost) at once, what will happen to the size of the atria?

It will get smaller as it contracts

Why isn't the repolarization of the atria visible on the ECG?

It's masked by the large QRS complex, which shows ventricular repolarization

What are the two main heart sounds, and what causes each one?

Lub - ventricular systole (emptying) Dub - ventricular diastole (filling)

As an impulse leaves the SA node, the myocytes of the atrial syncytium will depolarize. What happens to muscle cells when they depolarize?

Muscle cells contract when they depolarize.

Do the AV valves open only during atrial systole?

No, also during ventricular diastole/Atrial diastole

Will cells in the SA node be able to repolarize as quickly as other excitable cells? Why or why not?

No, don't allow K+ ions to leave the cell as rapidly as most excitable cells, takes longer to repolarize, leaving it closer to threshold if it does not repolarize all the way, making it more likely to reach threshold spontaneously

Will the connective tissue that separates the atrial syncytium from the ventricular syncytium conduct an impulse?

No, the connective tissue will not conduct an impulse. It will get to the ventricles this way: Junctional fibers -> AV node -> bundle of His -> conducting fibers

Clenched vs open fist

Open - diastole, clenched - systole

Explain why the anatomy of the ventricular CCS is optimal for emptying the ventricles

Purkinje fibers begin branching at the apex, meaning the signal is propagated from the apex, allowing for complete contraction (similar to squeezing a toothpaste tube from the bottom)

Which part of the ECG will be affected by the bundle branch block? What might you expect fo happen on the ECG?

QRS complex - two peaks instead of one or smaller peak as both are not occurring at the same time

Quiescent period of the cardiac cycle refers to the period when both syncitia are in diastole. What is occurring in the heart during the quiescent period?

Relaxation before chambers begin to refill

Where does the cardiac impulse originate?

SA node

Sometimes an infection might damage a portion of the CCS requiring the implantation of an artificial pacemaker. What portion of the CCS is this artificial pacemaker replacing?

SA node, electrical signaling between ventricles, natural rhythm.

What effect will the diameter of the fibers have as the impulse travels toward the AV node?

Similar to squid axons -> larger diameter means less resistance, faster signal propagation

As an impulse travels along the fibers leaving the SA node, it contracts atrial myocytes. What will happen to the myocytes that come into contact with these fibers?

The impulse will travel to those myocytes and then to other touching myocytes through gap junctions

What would happen if the impulse were to travel to the AV node before it had propagated throughout the atrial syncytium?

The signal would travel to the right ventricle before the right atrium had that signal propagated, potentially causing 2 chambers to contract at the same time

Why are the junctional fibers the diameter they are?

Thinner than AV bundle, etc - slower signal propagation is favorable to prevent the impulse from traveling to the AV node prematurely

Explain why ventricular fibrillation is life-threatening and requires the use of a cardiac defibrillator.

Ventricles are larger contributors to heartbeat; irregular heart rate can be dangerous.

What is occurring in the heart electrically when the QRS complex is being recorded?

Ventricular depolarization, atrial repolarization

When the AV valves open, is pressure higher in the atria or ventricles? What about when the SL Valves open?

Ventricular pressure is higher in both circumstances

What is occurring in the heart when the T wave is recorded?

Ventricular repolarization

Will the ventricles still contract if one of the bundle branches is impaired (called a bundle branch block)?

Yes, but it will take longer b/c impulse is delayed, making one ventricle slower than the other

Three layers of heart

endocardium (epithelium and connective tissue), myocardium (muscle tissue), epicardium (outer protective layer)

How does the amplitude of the P wave compare to that of the QRS complex?

much smaller

Which event is actually being shown on the ECG as the QRS complex?

ventricular depolarization

What percentage of ventricular volume is filled passively (without atrial systole)?

~80%