The penis is the male sex organ. It contains a tube called the urethra, which carries urine from the bladder to the outside of the body. The urethra also carries semen (sperm) from the testicles to the outside of the body. So the penis is part of the urinary system and the reproductive system.
The base of the penis is actually inside the body and is called the root. The penis extends from the root, outside the body and hangs in front of the pouch of skin called the scrotum. The scrotum holds both testicles.
The main part of the penis is called the body, or shaft. The tip of the penis is called the head or glans and is covered by a moveable layer of skin called the foreskin. Some men have an operation called a circumcision to remove their foreskin. Below the head of the penis is a ridge called the frenulum. For most men, the frenulum is the most sensitive part of their penis.
The penis is made up of different types of tissue including skin, muscle and nerves. It has a very rich blood supply so that it can become upright (an erection) during sexual activity. When sexually aroused, blood flow to the penis increases. Columns of special muscle tissue in the main body of the penis (erectile tissue) fill up with blood, and this makes the penis erect