Which component of the male reproductive system surrounds a portion of the urethra and helps expel semen?

The prostate gland plays a crucial role in the male reproductive system, particularly in the expulsion of semen. It surrounds a portion of the urethra, specifically the prostatic urethra, which runs through the prostate itself. The prostate's main function is to produce a fluid that nourishes and helps transport sperm during ejaculation. This fluid is a key component of semen and helps with the motility and viability of sperm as they are expelled through the urethra.

During ejaculation, contractions of the prostate gland help to propel this fluid into the urethra, facilitating the expulsion of semen out of the body. The gland's muscular tissue contracts rhythmically to assist with this process, highlighting its importance in male reproductive physiology.

In contrast, the epididymis primarily functions in the maturation and storage of sperm, the seminal vesicles contribute fluids that form a significant part of semen but do not surround the urethra, and the bulbourethral glands secrete a pre-ejaculatory fluid but are not involved in the expulsion of semen in the same manner as the prostate gland.