Which gland is located near the urethra in males and contracts during ejaculation to prevent urine flow?

The prostate gland is essential for male reproductive and urinary functions. Situated just below the bladder and encircling the urethra, it plays a critical role during ejaculation. When a male ejaculates, the prostate gland contracts to release prostatic fluid, which is a significant component of semen. This contraction also serves a crucial purpose of compressing the urethra, which prevents urine from mixing with the semen and inhibits urine flow during ejaculation. This dual function is vital for reproductive health, maintaining the integrity of both the urinary and reproductive systems.

In contrast, the seminal vesicles primarily produce a fluid that nourishes sperm but do not function to prevent urine flow. The bulbourethral glands, while they do produce a pre-ejaculatory fluid that can help lubricate the urethra, do not have the main responsibility of contracting to prevent urine flow. The vas deferens is a duct that transports sperm from the epididymis but is not involved in the secretion of fluids or in the contraction during ejaculation. Thus, the prostate gland's unique anatomical positioning and function during ejaculation makes it the correct answer in this context.