GRE Subject Test: Biology : Understanding Circulatory Functions
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Example Questions
Example Question #1 : Understanding Circulatory Functions
What is the function of arteries in the body?
To carry only oxygenated blood away from the heart
To exchange nutrients with the body's tissues
To return blood to the heart
To carry both oxygenated and deoxygenated blood away from the heart
To carry both oxygenated and deoxygenated blood away from the heart
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 #1 : Understanding Circulatory Functions
Which portion of the conduction system acts as the "pacemaker" of the heart, and spontaneously conducts action potentials?
Bundle of His
Atrioventricular node
Atrioventricular septum
Sinoatrial node
Sinoatrial node
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 #1 : Understanding Circulatory Functions
The shape of which blood vessel type can be altered in order to redirect blood flow?
Capillary
Arteriole
Venule
Artery
Arteriole
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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