All MCAT Biology Resources
Example Questions
Example Question #826 : Biology
Blood returning from the lungs enters into which chamber of the heart?
Right ventricle
Left ventricle
Left atrium
Right atrium
Left atrium
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 #827 : Biology
Which of the following accurately shows the electrical pathway through the heart?
Purkinje fibers, bundle of His, AV node, SA node
Purkinje fibers, SA node, AV node, bundle of His
AV node, SA node, bundle of His, purkinje fibers
SA node, AV node, bundle of His, purkinje fibers
SA node, AV node, bundle of His, purkinje fibers
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 #828 : Biology
Which valve in the heart separates the right atrium from the right ventricle?
Pulmonic valve
Bicuspid valve
Mitral valve
Tricuspid valve
Tricuspid valve
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 #831 : Biology
Which of the following statements most accurately describes the cardiac output (CO) of the heart?
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 the volume of blood pumped by a ventricle every minute (volume/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)
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 #832 : Biology
Cardiac muscle cells are electrically linked to each other through which of the following?
Cholinergic receptors
Pressure receptors
Gap junctions
Synaptic junctions
Axonal extensions
Gap junctions
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 #833 : Biology
Which cardiac valve prevents backflow of blood from the left ventricle into the left atrium?
Mitral Valve
Tricuspid Valve
Aortic Valve
Pulmonary Valve
Mitral Valve
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 #834 : Biology
What are the valves between the right atrium and right ventricle, and between the left atrium and left ventricle, respectively?
Tricuspid valve; mitral valve
Aortic valve; bicuspid valve
Bicuspid valve; tricuspid valve
Mitral valve; pulmonary valve
Tricuspid valve; mitral valve
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 #835 : Biology
Which is the only valve in the heart to have two operational flaps?
Semilunar valve
Tricuspid valve
Pulmonary valve
Mitral valve
Mitral valve
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 #836 : Biology
When blood moves from the right atrium to the right ventricle, it must pass through which heart valve?
It does not pass through any valve
The tricuspid valve
The mitral valve
The pulmonary valve
The semilunar valve
The tricuspid valve
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 #837 : Biology
The firing of which group of cells initiates contraction of the left and right ventricles?
Bundle of His
Purkinje fibers
Atrioventricular node
Sinoatrial node
Atrioventricular node
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.