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Correct Answer: C

Section: Physiology

The atrial stretch receptors are depolarized by stretch of the atria proportional to the magnitude of venous-

filling pressure. The frequency of action potentials rises to a maximum at the peak of the atrial "v" wave,

which signals maximum atrial filling during ventricular contraction. Although the remaining choices (A, B,

D, and E) may be influenced by the filling of the heart by venous pressure, the information conveyed to the

brain via the atrial stretch receptors relates directly to the filling pressure of the atria themselves.

Correct Answer: A

Correct Answer: D

Section: Pharmacology Although there are several forms of vitamin D and both vitamin D and parathyroid hormone act on the intestine, kidney, and bone, the net effect of vitamin D is to increase serum calcium and phosphate, while parathyroid hormone increases serum calcium and decreases phosphate. None of the other options (choices AC, E) correctly reflects the actions of vitamin D or parathyroid hormone.

Correct Answer: A

Section: Behavioral Science and Biostatics Anxiety or concomitant stress is a common trigger for help-seeking behavior, especially if the symptom or sign is of long duration. Although depression (choice B) can cause vague discomfort and precipitate help seeking, insisting on an operation immediately seems to indicate anxiety rather than depression, which is more likely to cause indecision or inaction. A drug-dependent person (choice C) is more likely to insist on drugs. There is no evidence of psychosis (choice D).

Correct Answer: D

Section: Physiology A light spot exclusively hitting the center would be perceived as deep red. Some of the light hits the inhibitory surround area. In this area, light is processed coming from cones that are best excited by green light (middle wavelength) and inhibited by red light (long wavelength). In the below figure the on-response dominates the off-response so that the perceived light is different from deep red, but not green (choice B). At the retina ganglion level, the trichromate signals from the cones are transferred into the neuronal stage of color processing, the opponent color stage. The cone photoreceptors are linked together to form opposing color pairs, in this case red versus green. Activation of one member of the pair inhibits the activity in the other so that a color pair cannot be seen at the same location. We cannot experience reddish green (choice E). Physiological color image formation differs from the physical process of coloring a piece of paper with a red and green pencil (choice A), one on top of the other, called subtractive color mixture. It starts with the presence of all colors of light and then dyes subtract some of the reflected light so that adding more dyes results in a darker image such as brown. For physiological color mixing, the presence of all colors is perceived as white, the absence as black (choice C).