Human Penis is composed of three distinct cylinders, two of which are responsible for the erectile functions and takes up much of the volume and muscle mass. These three cylinders are covered with thick and sturdy yet very flexible sheath of muscles which is called tunica Albiginea.
The urethra is located in the third cylinder known as corpus spongiosum which is encased in a relatively thinner muscle tissue. What is commonly identified as the glans or the head of the penis is actually the end part of the third cylinder which also extends down into the base.
While each of the cylinders is secured with its own sheaths, the three cylinders combined are then covered by the Buck’s fascia, a thick membrane which is finally enclosed in another sheet of skin known as the Colles fascia. The penis is able to erect because of the flexible and supple layers of skin around it.
A certain group of blood vessels traverses from the spine to the penis. These blood vessels get their supply from the main channel known as the aorta. Interestingly, the glans or the head which is a part of the third cylinder gets its supply of blood from a distinctly separate nerve group.
Nerve endings which serve as the sensory system of the penile area are primarily situated in the glans. Erection, sustained hardness and firmness as well as ejaculation are controlled by this sensory system.
Finally, a penis has the following external parts:
1. The shaft. It is the entire length of the organ that is visible from the base to the tip. This is the part that erects upon arousal and goes back to its flaccid non-erect state after the termination of sexual stimulus.
2. Glans. As aforementioned, this is the overly sensitive head where the urethra is found. Because it is always exposed to urine and semen, it deserves attention and extra care in terms of hygiene to avoid onset of infection, especially among uncircumcised men.
3. Frenulum. A very sensitive part located right at the base of the glans and at the end of the shaft on the underside of the penis.
4. Foreskin. It is the thick and movable covering of the glans which is removed during circumcision. Interestingly, there is currently and ongoing heated debate as to the propriety and necessity of circumcision.
5. Urethra. This is the channel through which semen and urine are excreted out of the body. Its one end is anchored in the bladder while the other end goes all the way to the tip of the penis.