Why doesn't semen enter the urinary bladder during ejaculation? Why doesn't semen enter the urinary bladder during ejaculation? The smooth muscle sphincter at the base of the urinary bladder closes. There is no common duct between the reproductive system and the urinary system. Ejaculation is a parasympathetic reflex resulting in no response by urinary contraction muscles. There is no urge to urinate during sexual intercourse because of the suppression of LH by testosterone buildup in the blood.