A gland located at the base of the penis. The prostate surrounds the neck of the bladder and the urethra. While it is a gland, it also contains muscle tissue, and is surrounded by nerves. It plays an important role in, erection, arousal, and orgasmic response; not only does it produce prostatic fluid, which comprises 20-30% of semen, its smooth muscles pulse during orgasm and play a significant role in expelling the ejaculate.