Key points:

• The ureters and urinary bladder are retroperitoneal organs, which means that they lie behind the peritoneum (the peritoneum is discussed in depth, elsewhere).
• The tunics (aka, layers) of their walls are specialized to accommodate changes in urine volume and to actively move urine through the urinary tract.
• The paired ureters conduct urine from the kidneys to the urinary bladder;
• The urinary bladder stores and expels urine.

Ureter Tunics:

• Adventitia, which is its outermost layer
• Muscularis, which comprises an outer circular and inner longitudinal layer
• Mucosa, which comprises the lamina propria and transitional epithelium
• Notice that the ureter does not have a submucosa.
• Transitional epithelium comprises cells that change shape to accommodate changes in urine volume; thus, we’ll see it also in the urinary bladder.

Urinary Bladder Tunics:

• Adventitia, its outermost layer
• Muscularis, which comprises the detrusor muscle, a collection of three layers of smooth muscle; the detrusor muscle contracts to expel urine and relaxes during urine storage
• Submucosa, which comprises connective tissues that support the urinary bladder walls
• The mucosa, which, like the mucosa of the ureter, comprises lamina propria and transitional epithelia

Features of Urinary Bladder:

• Mucosal rugae on the internal surface of the urinary bladder; as in the ureter, these folds facilitate expansion to accommodate urine.
• Ureters empty into the posterior/inferior bladder wall.
• Internal urethral orifice is opening at neck of the bladder; this is where urine exits the urinary bladder.
• Trigone, is a smooth, triangularly shaped portion of the bladder wall; its shape and smooth surface act as a sort of funnel to direct urine from the openings of the ureters to the urethra.

Clinical Correlation:

Detrusor overactivity is characterized by involuntary detrusor muscle contractions, which can cause urinary incontinence.