Once urine passes through the collecting ducts and enters the renal papilla, it will be delivered by the ureters to the urinary bladder. Urothelium lines the ureters, bladder, and the urethra. The urothelium is also referred to as transitional epithelium because it can transition from a plump rounded epithelium in a contracted bladder to a flattened epithelium in a distended urine-filled bladder. The urothelium is enveloped by a lamina propria and smooth muscle that is arranged in two layers (inner longitudinal and outer circular). Urinary bladder innervation it is under control of both the parasympathetic and sympathetic nervous system. Contraction of the urinary bladder occurs with the parasympathetic system via the pelvic nerve. The sympathetic nervous system relaxes the bladder smooth muscle and contracts the urethral smooth muscle (to keep urine from leaking out) via the hypogastric nerve.
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