PenisAnatomy & Physiology
ANATOMY OF THE PENIS
The internal structure of the penis consists of two cylinder-shaped vascular tissue bodies (corpora cavernosa) that run throughout the penis; the urethra (tube for expelling urine and ejaculate); erectile tissue surrounding the urethra; two main arteries; and several veins and nerves. The longest part of the penis is the shaft, at the end of which is the head, or glans penis.
Penis anatomy is remarkably complex: Following is the definitions for the most
cavernosa are two chambers that fill most of the
penis. The chambers are filled with a spongy tissue that
includes muscles, open spaces, veins and arteries. An
erection occurs when the corpora cavernosa become
engorged with blood and expand.
The Tunica Albuginea
called the tunica albuginea surrounds the corpora
cavenosa. This membrane helps keep blood in the
penis during an erection.
The urethra is the tube
through which urine travels. Ejaculate also travels
through the urethra. It runs down the underside of the
penis, beneath the corpora cavernosa and widens at its
opening, called the meatus. The meatus is located
at the glans (the head of the penis).
The corpus spongiosum is a chamber that surrounds the
urethra. It becomes engorged with blood during an
The prostate is a small gland located in the pelvis.
It surrounds the urethra and plays an important role in
ejaculation. Sperm, which is produced in the testicles
and stored in the seminal vesicles, is mixed with prostatic fluid and secretions from the
bulbourethral gland to form semen. During ejaculation,
semen is expelled through the urethra from the
STRUCTURE OF THE PENIS
illustration represents an average normal adult human
penis. The head of the penis (glans) has a covering,
called the foreskin (prepuce). This covering folds in on
itself, forming a double layer. The foreskin is not a `flap' of skin on the end of the penis, and
it is not `useless' or `redundant' skin.
There is some natural variation in the length of
the foreskin, which often covers a bit more or less of
the glans than illustrated.
- The outer foreskin layer is
a continuation of the skin of the shaft of the
- The inner foreskin layer is
not properly `skin', but mucocutaneous tissue of a
unique type found nowhere else on the body.
- The frenar band is the
interface (join) between the outer and inner foreskin
layers. When the penis is not erect, it tightens to
narrow the foreskin opening. During erection, the
frenar band forms a ridge that goes all the way
around, about halfway down the shaft.
- The reddish or purplish glans or glans penis (head of the penis)
is smooth, shiny, moist and extremely
- The frenulum, or frenum, is a connecting membrane on the
underside of the penis, similar to that beneath the
The foreskin has twelve known functions.
- To cover
and bond with the synechia so as to permit the
development of the mucosal surface of the glans and
protect the infant's glans from feces and ammonia in
protect the glans penis from friction and abrasion
- To keep
the glans moisturized and soft with emollient
lubricate the glans.
- To coat
the glans with a waxy protective substance.
provide sufficient skin to cover an erection by
provide an aid to masturbation and foreplay.
- to serve
as an aid to penetration.
reduce friction and chafing during intercourse.
- To serve
as erogenous tissue because of its rich supply of
contact and stimulate the G-spot of the female
PHYSIOLOGY OF ERECTION
The physiological process of erection begins in
the brain and involves the nervous and vascular systems.
Neurotransmitters in the brain (e.g., epinephrine,
acetylcholine, nitric oxide) are some of the chemicals
that initiate it. Physical or psychological stimulation
(arousal) causes nerves to send messages to the vascular
system, which results in significant blood flow to the
penis. Two arteries in the penis supply blood to
erectile tissue and the corpora cavernosa, which become
engorged and expand as a result of increased blood flow
Because blood must stay in the penis to maintain
rigidity, erectile tissue is enclosed by fibrous elastic
sheathes (tunicae) that cinch to prevent blood from
leaving the penis during erection. When stimulation
ends, or following ejaculation, pressure in the penis
decreases, blood is released, and the penis resumes its
HOW YOU GET AN
erection starts when you become sexually
nervous system sends chemical messages to your pelvic
area. The smooth muscles inside your penis relax. The
arteries widen. The corpora cavernosa, acting like a
sponge, fill with blood. In fact, the corpora absorb up
to eight times more blood than when your penis is
your penis swells and lengthens, the filled corpora
cavernosa press against the veins. The pressure greatly
reduces the blood flow from your penis. This keeps your
erection firm enough for intercourse. When
everything works the way it should, you will keep your
erection for as long as you are sexually
most important components of the physical erogenous
stimulation of the penis during foreplay and intercourse
are the sensations from the foreskin, frenulum/frenar
band, and glans. These structures each have their own
feeling, and each contributes in its own way to the
man's total experience of lovemaking. It must be
emphasized that emotional excitement is an extremely
important component of sexual enjoyment, and intensifies
the man's perception of any physical sensations from his
The foreskin has an
inner and outer layer. The outer foreskin layer contains
nerve endings which respond to gentle touching during
the early stages of sexual arousal. This helps to
trigger an erection. The nerves of the inner and outer
foreskin contribute to the experience of penile
stimulation, up to and including orgasm. These receptors
are stimulated by stretching, or when the foreskin rolls
over the surface of the glans during intercourse or
The foreskin contains sensory
receptors called Meissner corpuscles. We believe
that these nerves, similar to nerve endings in the
fingertips, are there to provide pleasure, as well as
fine sensory perception. This seems to help a man to
enjoy sex longer without ejaculating prematurely,
because he can more easily tell when he is approaching
the threshold of orgasm.
Stimulation of the frenulum and frenar band results in intense pleasurable
feelings during arousal. The frenar band consists of a
number of "ridges". Sensations from these structures
during intercourse or masturbation are thought to be the
primary trigger of orgasm in the intact male.
THE ANATOMY OF
Our bodies go through a number of
changes during sex. Understanding these changes
helps us understand both our sexuality and that of our
spouse. Most scientific folk divide these sexual
responses up into four phases - arousal, plateau,
orgasm, and resolution.
AROUSAL - This phase
starts with some kind of sexual stimulation - a touch, a
sight, or a thought. Blood begins to move to various
parts of the body. The lips, nipples (sometimes
nipples become erect), earlobes and genitals become
fuller and more sensitive. The penis begins to
fill with blood and become erect, and the scrotum starts
to thicken, pulling the testicles closer to the man's
PLATEAU - With continued
stimulation, the penis becomes slightly firmer, may
darken in color, and fluid containing sperm begin to
seep out. Over long periods of foreplay, the penis
ORGASM - The