When referring to male anatomy, the shaft is the length of the penis that runs from the scrotum to the glans or head. It is comprised of three different cylinders of soft and spongy tissue, known as erectile tissue. Each cylinder contains numerous small blood vessels which make the shaft sensitive to pressure, temperature, and touch. These blood vessels fill with blood during sexual arousal, causing an erection. The urethra, which transports urine and semen through the penis, also runs through the erectile tissue.
The shaft is also sometimes referred to as the body of the penis.