GRE Subject Test: Biology : Understanding Circulatory Functions

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Circulatory Functions

What is the function of arteries in the body?

Possible Answers:

To carry only oxygenated blood away from the heart

To carry both oxygenated and deoxygenated blood away from the heart

To exchange nutrients with the body's tissues

To return blood to the heart

Correct answer:

To carry both oxygenated and deoxygenated blood away from the heart

Explanation:

Many people have the misconception that arteries only carry oxygenated blood that has been pumped out fo the heart. The truth is that arteries are responsible for carrying all blood away from the heart, whether it be oxygenated or deoxygenated. For example, the aorta is an artery that carries oxygenated blood from the heart to the tissues, however, the pulmonary arteries carry deoxygenated blood from the heart to the lungs. Any vessel that travels away from the heart is classified as either an artery or an arteriole, regardless of the blood it contains.

Example Question #4 : Circulatory System

Which portion of the conduction system acts as the "pacemaker" of the heart, and spontaneously conducts action potentials?

Possible Answers:

Bundle of His

Atrioventricular node

Atrioventricular septum

Sinoatrial node

Correct answer:

Sinoatrial node

Explanation:

Action potentials are spontaneously conducted so that the heart can pump automatically, without necessary stimulation from the central nervous system. These spontaneous action potentials are created by a group of cardiac cells called the sinoatrial node. Because it determines the heart rate, the sinoatrial node is considered the pacemaker of the heart.

After generation by the sinoatrial node, action potentials will cause the atria to contract and travel to the atrioventricular node. The atrioventricular node introduces a delay, which prevents the ventricles from contracting during atrial systole, which could push blood backward from the ventricle to the atrium. The atria relax and the signal is passed from the atrioventricular node to the bundle of His in the atrioventricular septum before spreading to the ventricles and causing ventricular systole.

Example Question #3 : Understanding Circulatory Functions

The shape of which blood vessel type can be altered in order to redirect blood flow?

Possible Answers:

Venule

Capillary

Arteriole

Artery

Correct answer:

Arteriole

Explanation:

Blood vessels can be constricted or dilated in order to adjust blood pressure and reroute blood to areas in need of nutrients and oxygen. This constriction is done by smooth muscle, which is primarily found wrapped around arterioles.

Arteries also have a thick lining of smooth muscle, but are generally too large in diameter to be useful in directing blood flow. Capillaries have no smooth muscle and cannot be used to direct blood. Venules may have small layers of smooth muscle, but are not nearly as effective as arterioles.

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