Ureters and Urinary Bladder (urothelium)

Kidneys

• Filter the blood to produce urine;

Ureters

• Drain the kidneys medially (from the hilum), and descend along the posterior abdominal wall and into the pelvis, where they drain into the urinary bladder

Urinary bladder

• Stores urine until micturition

Ureter histology

Three tunics

• Adventitia; recall that retroperitoneal organs, including the ureters and urinary bladder, have adventitia as their outer tunic instead of serosa (which comprises visceral peritoneum).
• Muscularis layer
  • Outer circular, which wraps around the diameter of the ureter
  • Inner longitudinal, which runs the length of the ureter
• Mucosa
  • Opens to the lumen of the ureter; the mucosal folds unfurl to increase the diameter of the lumen and accommodate urine.
  • Outer layer of lamina propria, which is a thick layer of connective tissues
  • Inner layer of transitional epithelium (aka, urothelium), which is continuous with the linings of the renal pelvis of the kidney and urinary bladder.
  • Transitional epithelium comprises irregularly shaped cells that change shape to accommodate changes in urine volume; thus, we'll see it also in the urinary bladder.

Urinary Bladder Histology

• Adventitia is the outermost layer
• Muscularis 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, comprises connective tissues that support the urinary bladder walls, and,
• Mucosa, which, like the mucosa of the ureter, comprises folds of lamina propria and transitional epithelia (not shown, here).
  • Mucosal rugae of the internal surface of the urinary bladder facilitate expansion to accommodate urine.
  • Openings of the ureters on the posterior/inferior bladder wall and internal urethral orifice form the trigone, is a smooth, triangularly shaped portion of the bladder wall; its shape and smooth surface act as a funnel to direct urine from the openings of the ureters to the urethra.
  • Epithelium comprises basal cells, intermediate cells, and, in the apical layer, umbrella cells.
    Umbrella cells derive their name from their wide dome shape; because they face the urine, they have tight junctions, a mucin layer, and other features that form a barrier to water and urea.

Clinical correlation

• Transitional cell carcinoma is the most common type of bladder cancer; high-grade transitional cell carcinoma can spread through the muscular layer and to nearby organs and lymph nodes.

CT Scan

Images:

Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)