• Anatomical Overview
• Types of Cancer
• What is Cancer?

The bladder is a hollow, muscular, spherical organ which sits within the pelvis. Generally, its size correlates roughly to that of a large grapefruit, but in certain abnormal conditions, it can grow to much larger proportions. Its function is to collect and store the urine that has been made in the kidneys. Each side of the bladder is pierced by the small tubular ureter, which constantly transports the urine from each kidney. The base of the bladder opens into the urethra, much like a drain at the base of a sink. Normally, a circular muscular sphincter will coapt the walls of the urethra to keep the filling bladder from leaking urine. But at a certain point, the bladder is filled and, in a complex coordinated effort, the sphincter relaxes and opens the urethra while the muscular bladder simultaneously contracts. As urine flows out of the bladder and through the urethra (the urine passage through the penis), the bladder empties.

The inside of the bladder is covered by a smooth glistening water-tight surface of tissue known as mucosa. The cells that make up this tissue layer, referred to as transitional epithelial cells*, are the ones that most commonly may transform to grow into a bladder cancer. Of course, the wall of the bladder has several layers of cells of different tissue types, of which the transitional cell epithelium is the innermost or most "superficial" relative to its urinary surface. Deep to this layer is a layer of muscle cells, which make up the muscular layer of the bladder wall. This same muscular tissue layer is responsible for contracting the bladder to expel the urine. Surrounding the muscle, is the outermost layer, which is essentially made up of fat.

To understand bladder cancer progression, it is important to consider the organs that surround the bladder. In men, the prostate gland, which varies in size from that of a walnut up to the size of a small apricot, sits directly beneath the bladder. In fact the urethra passes straight through the prostate before it enters into the penis. In women, the urethra is very short and drains immediately in front of the vagina, which lies slightly behind and underneath the bladder. Directly behind the female bladder is the uterus. Directly behind the male bladder is the rectum. Therefore, depending on where in the bladder a tumor might grow, and whether it is in a male or female bladder, different organs can become affected.

*this cell layer is also known as the urothelium because it continues throughout the urinary tract, from the area of the kidney where urine collects through the top of the ureters where they connect to the kidney, down into the bladder, and throughout the majority of the urethra.