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Which capillary type has incomplete basement membranes wide enough to pass whole cells?
AThe sinusoid capillary
BThe fenestrated capillary
CThe continuous capillary
DThe metarteriole vessel
Answer & Solution
Correct answer: A. The sinusoid capillary
1. Capillaries come in three leakiness grades: continuous, fenestrated and sinusoid.
2. Sinusoid capillaries are flattened and carry extensive intercellular gaps plus incomplete basement membranes.
3. Those very large openings pass plasma proteins and even whole cells, which is how new blood cells leave the marrow.
4. Fenestrated capillaries have pores but keep their basement membrane, so they pass larger molecules and not cells.
5. A metarteriole is a feeding vessel with sphincters, not a class of exchange wall.
_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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