Final answer:
The trigone region of the bladder is marked by a smooth, thick mucosa without rugae. It is a stable area demarcated by the ureteral openings and urethral orifice, lined with transitional epithelium, and does not expand like other parts of the bladder.
Step-by-step explanation:
Within the trigone region of the urinary bladder, the mucosa is smooth, thick, and lacks rugae. The trigone is a triangular area at the base of the bladder, demarcated by the two ureteral openings and the urethral orifice. Unlike other regions of the bladder, the trigone's mucosa does not form rugae, which are the folds that allow for expansion. This area is also clinically important because it is less likely to stretch, providing a stable landmark within the bladder.
The entire bladder, including the trigone, is lined with transitional epithelium, which allows for expansion without damage as the bladder fills with urine. The urinary bladder's ability to expand is facilitated by this unique lining and the detrusor muscle, but the trigone remains smooth to ensure efficient urine flow from the ureters to the urethra.