Male sexual organs

Your penis is multipurpose, responsible for sexual pleasure, reproduction, and secretion of both urine and semen. The end of the penis, called the glans, contains the urethral opening that allows urine and semen to pass from the body. In uncircumcised men, an additional layer of skin covers the glans, and is referred to as the foreskin.

The main part of your penis is called the shaft, and the raised ridge that separates the shaft from the glans is called the corona. The entire penis is sensitive, but the glans and the corona are really sensitive. An erection occurs when your penis becomes stimulated, filling with blood and expanding. Though true of many other species, the human penis does not contain a bone.

Source: Purves et al. Life: The Science of Biology, 4th Edition. Reproduced with permission by Sinauer Associates.