Penis Anatomy

Penis Anatomy Images

One of the first lessons most kids with penises learn is that despite the common colloquialism, there are no bones in the penis. Beyond that most of us reach adulthood knowing remarkably little about this body part that takes up so much of our cultural imagination. 

The penis is made up of spongy tissue which fills with blood when a man is turned on or aroused, which usually results in an erection. There is a lot of variation in penis size although size has nothing to do with how well a penis is working or how much pleasure someone with that penis can give or receive. There are several different parts to the penis, each of which has some impact on feeling sexual arousal and pleasure.


The shaft of the penis is the part that extends out of the body to the tip of the penis. When flaccid (no erection) the skin on the shaft of the penis is loose and stretchy. While many people think that the shaft of the penis is not as sensitive as the head, some men have areas on the shaft that are highly sensitive. The shaft describes the part that is outside, but there is a small part of the penis that continues into the body, called the root of the penis.


The head of the penis is called the glans, and at the tip is the urethral opening (where both urine and semen come out). The glans is a highly sensitive area, with many nerve endings. The glans is often considered to be similar in function to the clitoris, as a fetus is developing the tissue that the glans develops out of is the same tissue that the clitoris develops from.


The frenulum is the indentation on the underside of the penis where the glans meets the shaft. For most the frenulum is an area of great sensitivity. In some cases the frenulum can be shortened, a condition called frenulum breve, which can cause sex play and intercourse to be painful.


Almost everyone born with a penis is born with a foreskin, the skin that covers the glans when the penis is flaccid. When the penis is erect, the foreskin retracts to just below the head. People who are circumcised have had their foreskins removed, so the glans is exposed at all times. There is a tremendous debate about the practice of circumcision for religious, cultural, and medical purposes. There is also debate about the connection between circumcision and sexuality.

Inside the Penis

The penis has no bones and no muscle in it. An erection happens as a result of stimulation and blood flow (and sometimes as a reflex). Inside the penis are three spongy tubes, two on top and one on the bottom. The bottom one also has the urethra running through it.

An erection happens when blood flows into the penis and fills the tissue making it firm. Erectile dysfunctions usually occur as a result of some problem with getting the blood to the penis, having enough of it flow in, or keeping the blood there.


The urethra is the tube through which urine and semen pass to get out of the body. The urethra runs from the bladder to the tip of the penis. In the process of normal functioning, there are certain passages that are blocked and others that open up to ensure that semen flows out of the urethra and not into the bladder, however, problems can happen which cause semen to not be expelled.

The urethra is also a sexual pleasure zone for some. Some people like the feeling of stimulation right at the urethral opening (which is called meatus) and others will stimulate the urethra itself. Internal urethral stimulation can cause serious harm, and it should only be engaged in with a great deal of education and care.