The bladder is a hollow organ that can comfortably hold about two cups of urine for approximately two to five hours, according to the National Kidney and Urologic Diseases Information Clearinghouse. Once the bladder fills to a comfortable limit, signals go to the brain to alert the body that the bladder is full and communicate the need to urinate. Once urination occurs, the bladder begins to fill again. At times, a failure in the signaling system prevents the bladder from releasing all of the urine, a condition known as urinary retention.

Neurogenic Bladder

Neurogenic bladder is a medical condition in which the muscles and nerves in the urinary system communicate improperly. The nerves that signal between the brain and bladder also function incorrectly. The result of the miscommunication is urine leakage and urinary retention. Treatment for the condition depends on the reason for the nerve damage and includes medications and a catheter to relieve the bladder. Conditions that may cause nerve damage to the bladder include multiple sclerosis, injury or trauma to the pelvis, diabetes and infections of the central nervous system, according to the University of Maryland Medical Center.

Prostate Gland Enlargement

The prostate is a gland in men that sits just below the bladder and surrounds the urethra, which is the tube that allows urine to travel from the bladder to the outside of the body. As a man ages, the prostate can increase in size. The enlargement may also be due to an inflammation of the prostate gland. This enlargement narrows the urethra, blocking urine flow. Treatments to decrease the enlargement include medications and surgical procedures to remove prostate tissue.

Blockage

The kidneys may form crystals and solid materials in urine, referred to as kidney stones. As the kidney stones pass through the urinary system, they may cause a blockage. The stones can become trapped in the ureters, which are the tubes that connect the kidneys to the bladder, or in the urethra. The resulting blockage can stop the flow of urine out of the body. Kidney stones may also cause extreme pain as they move through the body.

Medications

Some medications have side effects that can cause urinary retention. Antihistamines, which are used to treat allergies and dry mucous, can cause the bladder to retain urine. Certain medications have anticholinergic, or nervous system, side effects including constipation, dry mouth, blurred vision and urinary retention. These medications generally help treat conditions such as stomach cramping, urinary incontinence and muscle spasms in the body. Some antidepressant medications may also cause the bladder to hold urine.