Question

Assertion [A]: The rate of glomerular filtration is high.

Reason [R]: The diameter of the afferent arteriole is smaller than that of the efferent arteriole.

• A. Assertion [A] is True and Reason [R] is False.
• B. Reason [R] is True and Assertion [A] is False.
• C. Assertion [A] is True and Reason [R] is True and is a correct explanation to [A].
• D. Assertion [A] is True and Reason [R] is True but is not a correct explanation to [A].

Answer 1

The correct option is A

Assertion [A] is True and Reason [R] is False.

Normally the afferent arteriole is of larger diameter than the efferent. This means that there is high resistance as the blood is forced from a wider vessel to a narrower one and this promotes filtration. If the arterial blood pressure remains constant, then the contraction of either vessel reduces blood flow as it increases resistance. However contracting each vessel has antagonistic effects on the filtration pressure. If the afferent arteriole contracts, there will be less of a pressure difference between the afferent and efferent arteriole and hence, there is reduced filtration pressure. However, if the efferent arteriole contracts, there is an increase in the pressure difference between the two, and thus, filtration pressure increases.