From the renal pelvis, the urine flows into the ureter is a hollow tube with a length of about 30 cm In the wall of the ureter has smooth muscles. They peristaltically be reduced 3-5 times per minute, moving the fluid towards the bladder, the bulk of the bladder wall consists of smooth muscle. In its reduction the cavity of the bladder almost entirely disappear. The thickness of bubble walls reaches 1.5 cm in adults, With complete relaxation of the muscles of the bladder capacity increases to 350-450 ml. However, under the influence of urine entering the bladder is strongly stretched, and the thickness of its wall can be reduced to 2 mm.
The volume of strongly stretched bubble reaches 700-1000 ml. In an empty bubble of his musculature is in a state very weak (1-2 cm water column) of the tonic, i.e., continuous cuts. As the flow of urine the force of the tonic contraction increases slightly. When the amount of urine reaches 200 to 300 ml, the first urge to urinate. They become frequent and strong tensile bladder of urine to 600-700 ml.