AP Biology : Cardiac Physiology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Cardiac Physiology

The sinoatrial node generates action potentials at a faster pace than normal heart rate. Why does the heart beat more slowly than the SA node would dictate?

Possible Answers:

The atrioventricular node requires multiple action potentials in order to continue the electrical signal through the heart.

The parasympathetic vagus nerve slows down the heart rate.

Half of the action potentials are dedicated to the contraction of the atria, and the other half are dedicated to the contraction of the ventricles.

Many of the action potentials are not large enough to cause a contraction of the heart.

Correct answer:

The parasympathetic vagus nerve slows down the heart rate.

Explanation:

The vagus nerve is responsible for slowing down the heart rate, and is able to "override" the faster, natural pace of the sinoatrial node. When the vagus nerve is severed from the heart, the heart will pump at the pace of the SA node.

Note that innervation is not necessary for the heart to continue beating; it is self-sustaining, but can be affected by innervation from the vagus nerve.

Example Question #1 : Understanding Electrical Stimulation In The Heart

Which of the following structures is NOT part of the cardiac conducting system?

 

Possible Answers:

Chordae tendinae

Purkinje fibers   

Sinoatrial node 

Atrioventricular bundle

Correct answer:

Chordae tendinae

Explanation:

The chordae tendinae (tendinous chords or heart strings) are physical structures located in the heart lumen that connect the muscular wall of the heart to the tricuspid and mitral valves via papillary muscles.

The other answer options are examples of cell bundles and tissues that orchestrate the electrical conduction through the heart. Signals begin at the sinoatrial node and transition to the atrioventricular node. They then pass through the atrioventricular bundle (or bundle of His) to the purkinje fibers, which coordinate simultaneous ventricular contraction.

Example Question #21 : Circulatory Physiology

What is the importance of the atrioventricular node's time delay upon receiving impulses from the sinoatrial node?

Possible Answers:

It allows the impulse to spread evenly throughout the heart

It gives the cardiac cells time to depolarize

It allows the atria to adequately fill with blood

It allows the ventricles to adequately fill with blood

Correct answer:

It allows the ventricles to adequately fill with blood

Explanation:

The sinoatrial node is responsible for initiating the contraction of the heart. Depolarization of the sinoatrial node coincides with atrial contraction. The depolarization travels very quickly to the atrioventricular node during this period. The atrioventricular node delays the spread of the impulse, preventing it from triggering ventricular contraction. This time delay allows the atria to fill the ventricles with blood before the impulse causes the ventricles to contract. Without this delay, an inadequate amount of blood would be pumped from the ventricles.

Example Question #2 : Cardiac Physiology

After deoxygenated blood enters the heart at the right atrium, what path does it take?

Possible Answers:

It travels through the right side of the heart, flows to the left side of the heart, and then enters the lungs before returning to the body

It exits the heart through the pulmonary veins, then returns through the pulmonary arteries

It follows the pulmonary circuit

It follows the systemic circuit

Correct answer:

It follows the pulmonary circuit

Explanation:

The circulatory system is composed of two primary regions: the systemic circuit and the pulmonary circuit.

The systemic circuit allows blood to travel from the heart to the tissues of the body, delivering nutrients and oxygen, and then returns the deoxygenated blood to the heart. Most arteries, arterioles, capillaries, venules, and veins are part of the systemic circuit. The systemic circuit essentially starts with the aorta and ends with the vena cavae.

The pulmonary circuit receives dexoygenated blood from the body and carries it to the lungs for reoxygentation, before returning it to the heart to enter the systemic circuit through the aorta.

In general circulation, the vena cavae empty into the right atrium. Blood then enters the right ventricle and enters the pulmonary circuit. It travels to the lungs through the pulmonary arteries, becomes reoxygenated in the capillaries of the lungs, then returns to the left atrium via the pulmonary veins. From the left atrium, blood enters the left ventricle and is transferred to the systemic circuit.

Example Question #2 : Cardiac Physiology

Output from the heart can be altered mainly by changing which two variables?

Possible Answers:

Stroke volume and blood pressure

Blood pressure and heart rate

Stroke volume and heart rate

Breathing rate and stroke volume

Correct answer:

Stroke volume and heart rate

Explanation:

Multiplying stroke volume by heart rate gives another measure called cardiac output. Stroke volume will be influenced by variables such as resistance in the arteries and contractility of the heart muscle cells, while heart rate will be influenced by variables such as emotional state and age. Both stroke volume and heart rate increase with exercise.

 

Example Question #3 : Cardiac Physiology

Which portion of the heart would you expect to be the largest in a person with systemic high blood pressure?

Possible Answers:

Left ventricle

Right ventricle

Left atrium

Right atrium

Correct answer:

Left ventricle

Explanation:

The left ventricle supplies oxygenated blood from the heart to the aorta so it can be distributed to the body. The left ventricle must overcome the forces in the aorta and arteries (e.g., blood pressure). The higher the blood pressure, the harder the left ventricle must contract to force blood out of the aortic valve. This leads to muscle growth and enlargement of the left ventricle over time.

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