In a cross-section of the upper two-thirds of a ureter, how is the smooth muscle of the muscularis externa typically arranged? A) Inner longitudinal layer and outer circular layerB) Inner circular layer and outer longitudinal layer C) Three massive layers of voluntary skeletal muscle D) A continuous ring of hard bone matrix answer this question correctly
Reading File
Finding Sources
The answer is confirmed by multiple authoritative histology and anatomy textbooks.
Answer: A) Inner longitudinal layer and outer circular layer
Explanation
In the upper two-thirds of the ureter, the muscularis externa consists of two smooth muscle layers arranged as:
- Inner longitudinal layer
- Outer circular layer
This is the opposite of what you find in most of the GI tract (which has inner circular/outer longitudinal), so it is a classic exam trap.
The third layer - an outer longitudinal layer - only appears in the lower one-third of the ureter (near the ureterovesical junction), giving that segment a three-layer arrangement (inner longitudinal + middle circular + outer longitudinal).
Why the other options are wrong
| Option | Why it's wrong |
|---|---|
| B) Inner circular / outer longitudinal | This is the GI tract arrangement, not the ureter |
| C) Voluntary skeletal muscle | The ureter contains smooth (involuntary) muscle throughout |
| D) Bone matrix | Completely incorrect - no bone in ureter walls |
Clinical relevance
The peristaltic contractions of these smooth muscle layers propel urine from the renal pelvis down to the bladder. The inner longitudinal fibers help shorten the ureter, while the outer circular fibers squeeze the lumen closed - working together to create effective peristaltic waves.
Sources: Histology: A Text and Atlas (Ross & Pawlina), PLATE 20.5 Ureter; Berek & Novak's Gynecology, p. 2980-2984; Campbell-Walsh-Wein Urology, Microscopic Anatomy of the Ureter
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