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Which tunic is normally the thickest layer in the wall of a vein?
AThe tunica intima
BThe tunica externa
CThe tunica media
DThe basement membrane
Answer & Solution
Correct answer: B. The tunica externa
1. Arteries and veins both carry three tunics: intima, media and externa.
2. In an artery the tunica media, packed with smooth muscle and elastic fibers, is the thickest layer.
3. In a vein that pattern inverts: the collagen rich tunica externa is normally the thickest tunic.
4. The tunica intima in a vein is thinner than the externa, so it cannot be the answer.
5. The basement membrane is a component inside the intima, not a tunic in its own right.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.1 Structure and Function of Blood Vessels_
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