Practice question · Multiple choice
Epithelial sheets are strictly avascular, yet they exhibit high metabolic activity across surfaces like the gut and kidney tubules. What structural constraint does this trade-off impose on epithelia specialised for exchange?
Hints
- From where do epithelial cells obtain their oxygen and metabolic substrates?
- How does diffusion efficiency change as the distance from the underlying capillary bed increases?
Show the answer
A. They must remain limited to a single layer of living cells
Why
Diffusion across unvascularised tissue drops sharply with distance; thus, active transport or rapid exchange requires a minimal diffusion pathway. Cilia move luminal fluids, not metabolic fuels, whilst the basement membrane acts as a passive anchor, not a vascular pump.
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More questions on Epithelial Tissue and Glands
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