When the testes are exposed to FSH from the pituitary, Sertoli cells within seminiferous tubules in the testes produce sperm through meiosis. Immature sperm leave the testes and enter the epididymis where they mature (see Figure 13.5 below). The process of sperm production takes 2-3 months. Mature sperm are stored in the tail portion of the epididymis. Upon sexual arousal, the penis becomes engorged with blood, causing the penis to grow in size and become rigid. A penis in this state is termed “erect”.
Erection and further sexual arousal and stimulation may lead to orgasm and ejaculation. During ejaculation, sperm leave the epididymis in testicular fluid through the vas deferens; this sperm-containing fluid combines with secretions from the seminal vesicle, prostate and the bulbourethral gland. The fluid (now called semen) leaves the penis through the urethra, propelled by repeated contractile muscle spasms that occur during orgasm.
Watch the video below for more details of how male reproductive anatomy and physiology work.