The bladder is a hollow organ in the lower abdomen that stores urine produced by the kidneys. It can hold about 400 to 600 milliliters of urine. When the bladder fills, nerve signals inform the brain, creating the urge to urinate. During urination, the bladder muscles contract to push urine out through the urethra. This process is controlled by both voluntary and involuntary actions. Proper bladder function is essential for maintaining fluid balance and overall health. Issues with bladder function can lead to conditions like incontinence or urinary retention.