STEP1 Exam dumps PDF | Exam-Dumps (Page: 34)

QUESTION: 166

An adult male becomes hypotensive during surgery because of blood loss. Intravenous administration of 500 ml of which of the following solutions will have the greatest effect in restoring blood volume, and thus blood pressure to normal?

blood plasma
distilled water
hypoosmotic NaCl
isotonic dextrose solution
isotonic saline solution

Answer(s): A

Explanation:

Intravenous solutions are distributed in the various body fluid compartments based on osmolality and their ability to penetrate the vascular wall and the cell membrane. The proteins in blood plasma will remain within the vascular compartment because of their low permeability across the vessel wall. Thus, 500 mL of blood plasma will remain in the vascular compartment. Water (choice B) passes across the cell membrane and the vascular wall easily. Hence distilled water will distribute itself between cellular and extracellular spaces, meaning only a small portion will actually contribute to blood volume, the other choices (C, D, and E) cross the vascular barrier and distribute partially to the extravascular space and thus are less effective intravascular volume expanders.

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QUESTION: 167

Using laboratory micropuncture technique, blood plasma is collected from both the afferent arteriole and efferent arteriole of a renal cortical glomerulus. Which of the following has the lowest afferent/efferent arteriole concentration ratio?

albumin
chloride
glucose
potassium
sodium

Answer(s): A

Explanation:

The process of glomerular ultrafiltration creates a tubular fluid that is essentially protein free. Hence, as plasma passes from the afferent arteriole, through the glomerular capillaries to the efferent arteriole, the protein albumin concentration rises as approximately 20% of the fluid is filtered out, leaving the albumin behind, giving an afferent/efferent arteriole concentration ratio of approximately 0.8. By contrast, the glomerular capillary membrane is freely permeable to water and other small particles such as glucose (choice A), chloride (choice B), potassium (choice D), and sodium (choice E), so their concentrations do not change as approximately 20% of water and solute are filtered into Bowman's capsule, giving afferent/ efferent arteriole concentration ratios of 1.0.

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QUESTION: 168

It is known that stretch receptors contained in the walls of the atria convey nerve impulses to the brainstem via the vagus nerve. Under normal conditions, these nerve impulses are most likely to occur during ventricular systole. What information is communicated to the brain by these nerve impulses?

arterial muscle contraction
diastolic arterial pressure
filling of the atrium by venous pressure
filling of the ventricle
systolic arterial pressure

Answer(s): C

Explanation:

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.

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QUESTION: 169

High-dose glucocorticoid therapy for treatment of rheumatoid arthritis remains highly controversial. It is widely agreed that it is highly effective in controlling acute rheumatoid inflammation, but it may also result in significant adverse effects. Complications of high-dose glucocorticoid therapy include which of the following?

excessive growth in children and acromegaly in adults
hyperkalemia
hyponatremia
suppression of the hypothalamicpituitary-adrenal axis
volume depletion

Answer(s): D

Explanation:

High-dose exogenous glucocorticoids suppress the adrenal neuroendocrine axis. Patients treated for longer than 2 weeks need to be tapered off glucocorticoids slowly to avoid adrenal insufficiency. Other complications of high-dose glucocorticoids include growth suppression, not excessive growth (choice A) in children and volume overload, not volume depletion (choice E). Hyperkalemia (choice B) and hyponatremia (choice C) are observed in adrenal insufficiency due to loss of mineralocorticoid effects and are not relevant to glucocorticoid therapy.

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QUESTION: 170

A 53-year-old healthy male undergoes an exercise stress test, running on a treadmill until a maximum exertion is obtained. Which of the following statements correctly describes effects of autonomic nerve activity on the cardiovascular system in such a healthy subject?

inhibition of parasympathetic nerves decreases total peripheral resistance
inhibition of parasympathetic nerves increases heart rate
inhibition of parasympathetic nerves increases total peripheral resistance
stimulation of parasympathetic nerves decreases the strength of cardiac ventricular contractions
stimulation of sympathetic nerves decreases the strength of cardiac ventricular contractions

Answer(s): B

Explanation:

Since cardiac SA nodal cells receive tonic input from both sympathetic and parasympathetic nerves, heart rate increases whenever sympathetic firing rate increases or parasympathetic firing rate decreases. In humans, the parasympathetic innervation of ventricular muscle is negligible (choice D), and the strength of contraction increases with increasing preload and with increasing sympathetic firing rate (choice E). With few exceptions, blood vessels are not innervated by parasympathetic nerves, and there is little effect of changes in parasympathetic tone on total peripheral resistance (choices A and C).

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USMLE STEP1 Exam (page: 34) USMLE Step1 Updated on: 16-Feb-2026

QUESTION: 166

Explanation:

QUESTION: 167

Explanation:

QUESTION: 168

Explanation:

QUESTION: 169

Explanation:

QUESTION: 170

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USMLE STEP1 Exam (page: 34)
USMLE Step1
Updated on: 16-Feb-2026