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The urinary tract system is a group of organs of the body, which are responsible for the excretion of urine. In humans, the urinary system includes 2 kidneys, a pair of tube-like structures, called the ureters, which connect the kidneys to the bladder. The bladder is connected to the urethra, which delivers the urine to the outside of the body. The primary function of the urinary tract system is to remove substances from the blood, to form urine and help to regulate various metabolic processes.

(Click an organ above to see its description.)

Bladder

Function
The urinary bladder is responsible for the storage of urine and delivers it into the urethra for excretion from the body.

Structure
The urinary bladder is a hollow, distensible, muscular organ. It is spherical in shape, however, the pressure of the surrounding organs causes its shape to become altered. When the bladder is empty, the inner wall retracts into many folds, but as it is filled with urine, the bladder wall expands and becomes smoother. The wall of the urinary bladder consists of four layers. The inner layer, or mucous coat, is composed of epithelial cells. The second layer, or submucous layer, is made up of connective tissue and contains many elastic fibers. The third layer, or muscular coat, is primarily made up of coarse bundles of smooth muscle fibers. These muscles in the muscular coat are interlaced to form the detrusor muscle. The portion of the detrusor muscle around the neck of the bladder forms an internal urethral sphincter, which controls the excretion of urine. The outer layer, or serous coat, is made of the parietal peritoneum. However, this layer occurs only on the upper surface of the urinary bladder, or bladder dome. Elsewhere, the outer coat is composed of fibrous connective tissue.