Anatomy and physiology of the bladder

The bladder is a hollow, balloon-shaped organ in the lower part of the abdomen (the pelvis). The bladder has a flexible, muscular wall that allows it to expand (get larger) and contract (get smaller).

Structure

The bladder wall is made up of three main layers:

• mucosa
  • a layer of transitional cells (urothelial cells) that line the inside surface of the bladder, ureters and urethra
  • also called transitional epithelium, urothelium, mucosal surface, transitional mucosa
• submucosa
  • a layer of connective tissue that lies just outside the mucosa, separating the mucosa from the muscularis
  • contains blood vessels, nerves and glands
  • also called lamina propria, suburothelial connective tissue, subepithelial tissue, stroma, muscularis mucosa
• muscularis
  • three layers of muscle tissue (bladder muscle) that lie just outside the submucosa – inner longitudinal, middle circular and outer longitudinal
  • also called muscularis propria, muscularis externa, smooth muscle

Additional layers of tissue separate the bladder from nearby organs:

• serosa, or serous coat – a thin membrane of connective tissue that is only on the higher surface of the bladder
• adventitia – connective tissue that covers areas of the bladder where there is no serosa
• perivesical fat – a layer of fat that surrounds the bladder, outside the serosa and adventitia

Function

The function of the bladder is to store urine. Urine is produced by the kidneys and travels to the bladder through two long tubes called ureters. The bladder can store up to 2 cups of urine on average. When a person is ready to urinate, the bladder's muscular wall contracts to expel the urine. The urine is emptied from the bladder through a tube called the urethra. In women, the urethra is a short tube in front of the vagina. In men, the urethra is longer and passes through the prostate gland and the penis.