alleryStart learning →How wide are the pores through which filtrate crosses from capillary to capsule?
AAbout 70 nm across
BAbout 7 nm across
CAbout 700 nm across
DAbout 0.7 nm across
Answer & Solution
Correct answer: A. About 70 nm across
1. The filtration membrane is built for speed as well as selectivity.
2. Its pores measure only 70 nm in diameter.
3. That is wide enough for very rapid bulk movement of fluid yet far too narrow for cells.
4. Molecular size limits are stricter still, since substances cross readily only below 4 nm.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.4 Microscopic Anatomy of the Kidney_
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