In the testicles sperm is produced in coiled structures known as seminiferous tubules The epididymis runs along the top of each testicle. This is a cord-like structure where sperm develop and are stored. When the penis fills with blood and gets erect the release process begins.
Sperm develop in the testicles within a system of tiny tubes called the seminiferous tubules. At birth, these tubules contain simple round cells. During puberty, testosterone and other hormones cause these cells to transform into sperm cells.