Pathology > Study Images > Urinary Tract > Tumors of the Urothelium > Anatomy & Histology
Objectives Anat & Hist Introduction Benign Tumors Malignant Tumors

I. Anatomy and Histology

Objectives:

After completing this tutorial the student will be able to:

  • describe the basic gross anatomy and histology of the renal pelvis, ureter and urinary bladder

  1. Anatomy

The renal pelvis is the funnel-shaped, expanded upper portion of the ureter. Within the renal sinus it divides into 2 or 3 major calyces, which in turn divide into minor calyces. The pelvis extends from the renal hilum and narrows outside the kidney to become the ureter. The ureter is a tubular structure, which descends more or less vertically in the retroperitoneal space, cross the iliac vessels at the pelvic brim and turn medially to enter the urinary bladder, running obliquely through its wall.

The urinary bladder is a hollow muscular organ shaped roughly like a tetrahedron when empty and spherical when filled with urine. The posterior triangle of the tetrahedron forms the base of the bladder, the anterior the apex, the inferior angle the apex, the inferior angle leadin to the urethra is called the neck and the two posterolateral angles admit the ureters. The smooth triangular area outlined by the ostia of the ureters and the internal orifice of the urethra is called the trigone. The uvula is the smooth, small ridge at the inferior corner of the trigone just above the internal urethral orifice.

  1. Histology

The mucosa of the renal pelvis, ureter and urinary bladder is lined by stratified epithelium, the urothelium or transitional epithelium (from the erroneous concept that this epithelium constitutes a transition between stratified squamous and columnar epithelia). The epithelium is 2-3 cells thick in the pelvis, up to 5 in the ureter and up to 7 cells thick in the bladder in the undistended state. The basal layer is formed by cuboidal to columnar cells while the superficial layer is made up of relatively larger cells, which may take on an "umbrella-like" shape due to their outer convex shape. Interposed between the two layers are polyhedral, intermediate cells. The urothelium lies on a thin, non-discernable basement membrane beneath which is the connective tissue of the lamina propria. There is no muscularis mucosae and the lamina propria rests on the muscle coat.


Normal bladder mucosa showing transitional epithelium and lamina propria.


Bladder wall. From left to right - lumen, transitional epithelium, lamina propria, thick layer of smooth muscle.


Transitional epithelium of the bladder. Transitional epithelium is a stratified epithelium characterized by the fact that the most apical cells are the roundest and largest in diameter. T.E. is designed to be able to increase its surface area as the lumen is dialated by urine.

The pelvis and ureter have two continuous thin muscle layers that originate in the minor calyces and form a spiral, helical arrangement with a loosely spiraled internal layer and a more tightly spiraled external layer in the ureter. In the lower third of the ureter, a third outer longitudinal layer is present. All 3 layers merge with the 3 layers (inner longitudinal, middle circular and outer longitudinal) in the bladder wall, which run longitudinally, transversely and obliquely.


Cross-section of ureter. It has a very irregular lumen, which is lined by transitional epithelium. Under the epithelium is a connective tissue layer and beneath that two layers of smooth muscle, inner longitudinal and outer circular.


Transitional epithelium is a stratified epithelium characterized by the fact that the most apical cells are the roundest and largest in diameter. T.E. is designed to be able to increase its surface area as the lumen is dialated by urine.

Beneath the outer muscle coat is the serosa, made up of loose connective tissue and containing blood vessels and lymphatics.

Objectives Anat & Hist Introduction Benign Tumors Malignant Tumors