ANATOMY

Detailed explanation-1: -The internal urethral sphincter relaxes, allowing for urine to pass out of the bladder into the urethra. Both of these reactions are involuntary. The external urethral sphincter is voluntary. It must be relaxed for urine to flow through the urethra and outside the body.

Detailed explanation-2: -Contraction of internal urethral sphincter stops the flow through the internal urethral orifice preventing the flow of urine from the bladder. The internal urethral sphincter is made of a layer of smooth muscle that is surrounded by striated muscle.

Detailed explanation-3: -At an appropriate time and place, the external urethral sphincter can then be voluntarily relaxed, allowing the passing of urine. A secondary function of the urethral sphincter complex is to prevent retrograde ejaculation of semen into the bladder. In males, semen and urine share the urethra as a passageway.

Detailed explanation-4: -The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of these muscles contracts, the urethra is sealed shut.

Detailed explanation-5: -The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax to let urine exit the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.