The penis is a male reproductive organ primarily composed of erectile tissue, blood vessels, and nerves. It has three main parts: the root, which connects to the pelvic bones; the body or shaft, which is the elongated part; and the glans, the sensitive tip. The penis also contains the urethra, a tube that carries urine and semen out of the body. Erectile tissue in the penis allows it to become firm and enlarged during sexual arousal. This process, known as erection, occurs when blood fills the erectile chambers, causing the penis to increase in size and rigidity. The ability to achieve and maintain an erection is essential for sexual intercourse and reproduction.