Health Library

(Click to Enlarge) The urinary bladder and urethra: These drawings show the difference
in the urethras of men (left) and women (right). The smooth muscle at the juncture
of the urinary bladder and urethra forms the internal sphincter. The pelvic diaphragm
is a flat sheet of muscle covering the lower boundary of the pelvic cavity. It forms
the external sphincter and is under voluntary control.

The bladder is a hollow organ in your lower abdomen. It’s the storage place for urine.
This is the liquid waste that’s made by the kidneys. Urine flows from each kidney
through a tube called a ureter. The ureters carry urine into the bladder. The urine
stays in the bladder until you urinate.

An outer layer of muscle surrounds the inner lining of the bladder. When the bladder
is full, the muscles in the bladder wall can be tightened to allow urination. Urine
leaves the bladder through another tube. This is called the urethra. After you urinate,
the bladder shrinks in size.

The bladder is made of several layers. These include the following:

• Urothelium or transitional epithelium: This is the layer of cells that lines
  the inside of the kidneys, ureters, bladder, and urethra. Cells in this layer
  are called urothelial cells or transitional cells.

• Lamina propria: This is the next layer down. It’s under the urothelium. It’s
  a type of connective tissue.

• Muscularis propria: This is the next layer. It’s under the lamina propria. It
  is muscle tissue.

• Fatty connective tissue: This separates the bladder from other organs.

Superficial bladder cancer affects only the lining of the bladder. This is the transitional
epithelium. Invasive bladder cancer goes into deeper layers of the bladder wall.