The bladder is the organ that collects and stores urine. It consists of muscle tissue, which is relaxed when in the resting state and is unusual in that it is highly elastic. Bladder capacity primarily depends on a person's height. Normal bladder capacity in adults ranges from 350–550 ml. Urination is a complex reflex which, in healthy individuals, can be consciously suppressed. Part of this reflex involves contracting the bladder muscles whilst simultaneously relaxing the urethral sphincter.
A number of diseases can affect bladder function. In this section, we will discuss the most common.