Micturition is urination. The ureters carry urine (by peristalsis) to the urinary bladder for storage. The ureters consist of transitional epithelium with circular and longitudinal muscle layers. They empty into the urinary bladder, which has a similar tissue structure. The maximum volume of the urinary bladder is about 700-800 mL. Rugae (folds) in the mucosa allow the bladder to expand.
When the bladder is partly full (about 250 mL), stretch receptors in its wall begin to respond. This parasympathetic reflex response causes detrussor muscle contraction in the bladder wall. Urine is pushed toward the urethra, forcing the internal urethral sphincter to open. The external urethral sphincter is under voluntary control and must relax to allow passage of urine. The urethra is short in females and longer in males.
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