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Which muscle types build the internal and external urinary sphincters, respectively?
ASkeletal, then cardiac muscle
BSmooth, then voluntary skeletal muscle
CCardiac, then smooth muscle
DSkeletal muscle for both of them
Answer & Solution
Correct answer: B. Smooth, then voluntary skeletal muscle
1. Voiding is regulated by two stacked sphincters.
2. The internal urinary sphincter is involuntary smooth muscle under autonomic control.
3. Below it, voluntary skeletal muscle forms the external urinary sphincter.
4. Cardiac muscle exists only in the heart, eliminating two options at once.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section Urethra_
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