MCAT Biology : Heart

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Heart

Blood returning from the lungs enters into which chamber of the heart?

Possible Answers:

Left atrium

Right atrium

Left ventricle

Right ventricle

Correct answer:

Left atrium

Explanation:

Oxygenated blood returning to the heart from the lungs enters the left atrium. It then goes to the left ventricle and out the aorta.

 

Example Question #2 : Heart

Which of the following accurately shows the electrical pathway through the heart?

Possible Answers:

AV node, SA node, bundle of His, purkinje fibers

Purkinje fibers, SA node, AV node, bundle of His

Purkinje fibers, bundle of His, AV node, SA node

SA node, AV node, bundle of His, purkinje fibers

Correct answer:

SA node, AV node, bundle of His, purkinje fibers

Explanation:

The correct electrical path through the heart is the SA (sinoatrial) node, AV (atrioventricular) node, bundle of His (AV bundle), then purkinje fibers.

The sinoatrial node initiates the electrical signal and acts as the heart's natural pacemaker. Innervation from the parasympathetic nervous system is crucial in maintaining a normal heart rate from the SA node, but is not required to initiate electrical signals. The signal travels to the atrioventricular node and is briefly delayed, allowing the atria to finish contracting before initiaing ventricular systole. The signal travels down the bundle of His and is quickly distributed to the purkinje fibers, which initiate ventricular systole.

Example Question #3 : Heart

Which valve in the heart separates the right atrium from the right ventricle?

Possible Answers:

Tricuspid valve

Pulmonic valve

Mitral valve

Bicuspid valve

Correct answer:

Tricuspid valve

Explanation:

The tricuspid valve separates the right atrium from the right ventricle. The bicuspid valve (also known as the mitral valve) separates the left atrium from the left ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery and the aortic valve separates the left ventricle from the aorta (these are known as the semilunar valves).

Example Question #4 : Heart

Which of the following statements most accurately describes the cardiac output (CO) of the heart?

Possible Answers:

Caridac output is the same as stroke volume (volume of blood pumped from each beat)

Cardiac output is the same as heart rate (beats/min)

Cardiac output is equal to the mean arterial pressure (MAP)

Cardiac output is the volume of blood pumped by a ventricle every minute (volume/min)

Correct answer:

Cardiac output is the volume of blood pumped by a ventricle every minute (volume/min)

Explanation:

Cardiac output is the product of heart rate (HR) and stroke volume (SV). Heart rate is equal to beats per minute, while stroke volume is equal to volume per beat. The "beat" units cancel, and leave the cardiac output equal to volume per minute.

cardiac output = (beats/min) * (volume/beat) = volume/min. 

Example Question #5 : Heart

Cardiac muscle cells are electrically linked to each other through which of the following?

Possible Answers:

Pressure receptors

Cholinergic receptors

Gap junctions

Synaptic junctions

Axonal extensions

Correct answer:

Gap junctions

Explanation:

Electrical coupling of cells is mediated through gap junctions—ions are able to immediately flow through adjacent cells through these transmembrane protein channels. Cardiac muscle requires such syncytial connections in order to most effectivey synchronize muscle contraction.

Neurotransmitters, synaptic junctions, and cholinergic receptors would necessitate a nervous system communication, but the heart is electrically-coupled without neural mediation. Pressure receptors are not involved in cardiac muscle activity.

Example Question #6 : Heart

Which cardiac valve prevents backflow of blood from the left ventricle into the left atrium? 

Possible Answers:

Tricuspid Valve 

Aortic Valve

Pulmonary Valve

Mitral Valve 

Correct answer:

Mitral Valve 

Explanation:

This a simple anatomy question. The mitral (bicuspid) valve lies between the left atrium and ventricle, therefore the answer must be the mitral valve. The tricuspid valve lies between the right atrium and ventricle.

Example Question #7 : Heart

What are the valves between the right atrium and right ventricle, and between the left atrium and left ventricle, respectively?

Possible Answers:

Aortic valve; bicuspid valve

Tricuspid valve; mitral valve

Mitral valve; pulmonary valve

Bicuspid valve; tricuspid valve

Correct answer:

Tricuspid valve; mitral valve

Explanation:

The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.

The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.  

Example Question #8 : Heart

Which is the only valve in the heart to have two operational flaps?

Possible Answers:

Mitral valve

Tricuspid valve

Pulmonary valve

Semilunar valve

Correct answer:

Mitral valve

Explanation:

The semilunar valves refer to the aortic valve and pulmonary valve, both of which have three flaps. The atrioventricular valves separate the atria from the ventricles. The right side of the heart is separated by the tricuspid valve, while the left is separated by the bicuspid, or mitral, valve. The mitral valve is the only heart valve with two flaps.

Example Question #9 : Heart

When blood moves from the right atrium to the right ventricle, it must pass through which heart valve?

Possible Answers:

The pulmonary valve

The mitral valve

It does not pass through any valve

The semilunar valve

The tricuspid valve

Correct answer:

The tricuspid valve

Explanation:

When blood passes from the right atrium into the right ventricle, it must pass through the tricuspid valve.

The mitral, or bicuspid, valve separates the left atrium and ventricle. The semilunar valves are the aortic and pulmonary valves. The aortic valve separates the left ventricle and aorta, while the pulmonary valve separates the right ventricle and pulmonary arteries.

Example Question #10 : Heart

The firing of which group of cells initiates contraction of the left and right ventricles?

Possible Answers:

Bundle of His 

Sinoatrial node

Atrioventricular node

Purkinje fibers

Correct answer:

Atrioventricular node

Explanation:

After axons from the sinoatrial node flow through the atria to cause atrial contraction, the depolarization pauses in the atrioventricular node. Once the atrioventricular node depolarizes, the electrical signal travels though the bundle of His to the walls of the ventricles via purkinje fibers. The atrioventricular node initiates ventricular contraction, the bundle of His carries the signal, and the purkinje fibers allow for synchronized contraction of different regions of the ventricular wall.

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