The male reproductive system includes internal structures like the testes, epididymis, ductus deferens, seminal vesicles, prostate, and penis. The testes are held in the scrotum and produce sperm. Sperm travel through the epididymis, ductus deferens, and ejaculatory duct before mixing with fluids from the seminal vesicles and prostate to form semen, which is ejaculated through the urethra in the penis during orgasm. Blood flows into the structures through arteries and drains out through veins, while nerves provide sensation and control erectile function and ejaculation.