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 layer
Reading File
Finding Sources
Reading File
The answer is A) Inner longitudinal layer and outer circular layer - and the textbook confirms this directly.
Ureter Muscularis Externa - Smooth Muscle Arrangement
Upper Two-Thirds of the Ureter
The muscularis of the upper two-thirds of the ureter has two layers:
| Layer | Position | Spiral Pattern |
|---|---|---|
| Longitudinal | Inner | Loose spiral |
| Circular | Outer | Tight spiral |
This is the opposite of the GI tract, where the circular layer is inner and the longitudinal layer is outer. This is a classic histology exam point.
Lower Third (Distal Ureter)
In the lower third, a third layer is added - an outer longitudinal layer - giving the arrangement: inner longitudinal / middle circular / outer longitudinal. This outer longitudinal layer is absent in the upper two-thirds.
Why Option A is Correct
From Histology: A Text and Atlas (Pawlina):
"Two layers of smooth muscle lie beneath the lamina propria: longitudinal layer, the inner layer... circular layer, the outer layer... Note that this arrangement of the smooth muscle is opposite to that of the muscularis externa of the intestinal tract."
The question specifically asks about a cross-section of the upper two-thirds, where only two layers are present: inner longitudinal and outer circular.
Histology: A Text and Atlas with Correlated Cell and Molecular Biology, p. 1936
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