Final answer:
The internal urethral sphincter in males surrounds the prostatic urethra, which passes through the prostate gland and is crucial for controlling urine flow and preventing the backward flow of semen into the bladder during ejaculation.
Step-by-step explanation:
The internal urethral sphincter in males surrounds the prostatic urethra. The prostate gland is where the internal urethral sphincter is located, immediately inferior to the bladder. This sphincter plays a vital role in the control of urine flow and is an involuntary sphincter, meaning it is controlled automatically by the autonomic nervous system. During ejaculation, the internal urethral sphincter contracts to prevent the backward flow of semen into the bladder.
It's important to note that both the prostate and the bulbourethral glands contribute to the components of semen, and the prostate is crucially located around the urethra, producing about 30 percent of the seminal fluid. The male urethra passes through the prostate gland, making the prostatic urethra a shared section of the male urinary and reproductive systems.