All of the following are components of sphincter of the lower genitourinary tract in females, EXCEPT:
**Core Concept**
The lower genitourinary tract in females is guarded by a complex sphincteric mechanism that ensures proper continence and prevents involuntary urine leakage. This sphincteric complex consists of muscles and structures that play a crucial role in maintaining urinary continence.
**Why the Correct Answer is Right**
The correct answer is the component that does not belong to the sphincter of the lower genitourinary tract in females. The external urethral sphincter is a voluntary muscle that surrounds the membranous part of the urethra, while the internal urethral sphincter is an involuntary muscle that surrounds the proximal part of the urethra. The urethral crest, on the other hand, is a longitudinal ridge on the posterior wall of the urethra that houses the urethral crest and seminal colliculus in males, but it is not a part of the sphincter mechanism in females. The urethral sphincter mechanism is primarily composed of the external urethral sphincter, the internal urethral sphincter, and the periurethral smooth muscles.
**Why Each Wrong Option is Incorrect**
**Option A:** The external urethral sphincter is a key component of the sphincter mechanism in females, so it is not the correct answer.
**Option B:** The internal urethral sphincter is another essential component of the sphincter mechanism in females, making it an incorrect option.
**Option D:** The periurethral smooth muscles play a crucial role in maintaining urinary continence, so it is not the correct answer.
**Clinical Pearl / High-Yield Fact**
The urethral sphincter mechanism is a complex entity that involves both voluntary and involuntary components, which work in concert to maintain urinary continence. Understanding the anatomy and physiology of this mechanism is essential for managing patients with urinary incontinence.
**Correct Answer:** C.