In anatomy class, the instructor asks, "Explain how urine is expelled from the bladder during voiding." The student with the most accurate response would be:

Question

A) "The urothelium acts as a barrier to prevent urine from seeping into capillaries."
B) "The beginning of micturition occurs when neurons send messages down to the pudendal nerve."
C) "The detrusor muscle contract down on the urine and the ureteral orifices are forced shut. The external sphincter relaxes as urine moves out of the bladder."
D) "It's really the external sphincter muscle that controls urination. The somatic nervous system innervates the muscles of the external sphincter and the pelvic floor muscles that together control the outflow of urine."

Answer 1

Ans: C
Feedback:
During the act of micturition, the detrusor muscle of the bladder fundus and bladder neck contracts down on the urine and the ureteral orifices are forced shut. The bladder neck is widened and shortened, and the external sphincter relaxes as urine moves out of the bladder. Descent of the diaphragm and contraction of the abdominal muscles raise intra-abdominal pressure and aid in the expulsion of urine from the bladder.