"According to the size of his sexual organ, a man is called a hare (shasha - six fingers long), bull
(vrisha - eight fingers), or stallion (ashva - twelve)." - from "Kama Sutra"
"The penis does not obey the order of its master, who tries to erect or shrink it at will. Instead,
the penis erects freely while its master is asleep. The penis must be said to have its own mind, by any stretch
of the imagination." - Leonardo da Vinci
Since ancient times many people were interested in the penis size and studied the penis ability to erect.
In this article you can find information about the penile anatomy and the concept of erection.
Historical penis studies
The first description of erectile dysfunction dates from about 2000 BC and
was set down on Egyptian papyrus. Two types were described: natural (the man is incapable of accomplishing the sex act)
and supernatural (evil charms and spells). Later, Hippocrates reported many cases of male impotence among the rich
inhabitants of Scythia and ascribed it to excessive horseback riding. The poor were not affected because they traveled
by foot. Aristotle stated that three branches of nerves carry spirit and energy to the penis and that erection is
produced by the influx of air. His theory was well accepted until Leonardo da Vinci noted a large amount
of blood in the erect penis of hanged men and cast doubt on the concept of the air-filled penis. In 1585
Ambroise Pare gave an accurate account of penile anatomy and the concept of erection. He described the
penis as being composed of concentric coats of nerves, veins, and arteries and of two ligaments (corpora cavernosa),
a urinary tract, and four muscles. "When the man becomes inflamed with lust and desire, blood rushes
into the male member and causes it to become erect."
Much of the current understanding of the penis erectile physiology was gained in the 1990s. In addition to
the role of smooth muscle in regulating arterial and venous flow, the three-dimensional structure of the
tunica albuginea and its role in venous occlusion were elucidated. An important breakthrough in the
understanding of neural influences was the identification of nitric oxide (NO) as the major neurotransmitter
for erection and of phosphodiesterases (PDEs) for detumescence. The role of endothelium in regulating smooth
muscle tone and of the intercellular links effected by gap junctions has been uncovered. Furthermore, the
importance of ion channels (potassium and calcium) and Rho/Rho kinase pathways in contraction and relaxation
of smooth muscle has been shown. In pathophysiology, changes in smooth muscle, nerve endings, endothelium, and
the fibroelastic framework associated with disease have been identified.
Functional anatomy of the penis
The penis is composed of three cylindrical structures, the paired corpora cavernosa and the corpus spongiosum
(which houses the urethra), covered by a loose subcutaneous layer and skin. Its flaccid length is controlled by
the contractile state of the erectile smooth muscle and varies considerably, depending on emotion and outside
temperature. In one study, penile length, measured from the pubopenile junction to the meatus, was 10.8 cm flaccid,
15.4 cm stretched, and 17.2 cm erect, with neither age nor the size of the flaccid penis accurately predicting
erectile length. In another study, the author concluded that about 15% of men have a downward curve during erection,
erect angle is below horizontal in one quarter, and shorter erect lengths occur in 40% of men. Since then, more studies
have been reported from several countries. Regarding penile morphology and erection, one study showed that, during
erection, the penile buckling forces are dependent not only on intracavernous pressures but also on penile geometry
and erectile tissue properties. The authors concluded that, in patients with normal penile hemodynamics, but without
adequate rigidity, structural causes should be investigated.
The source of penile blood is usually the internal pudendal artery, a branch of the internal iliac artery. In a study
of 20 fresh human cadavers, three patterns of penile arterial supply were reported. The internal pudendal artery
becomes the common penile artery after giving off a branch to the perineum. The three branches of the penile artery
are the dorsal, bulbourethral and cavernous. Distally, they join to form a vascular ring near the glans. There are also
helicine arteries, which are contracted and tortuous in the flaccid state, but become dilated and straight during
Penile components and their function during erection
- Corpora cavernosa - support corpus spongiosum and glans.
- Tunica albuginea - contains and protects erectile tissue, and promotes rigidity
of the corpora cavernosa.
- Smooth muscle - regulates blood flow into and out of the sinusoids.
- Ischiocavernosus muscle - pumps blood distally to hasten erection and provides additional penile rigidity
during erection phase.
- Bulbocavernosus muscle - compresses the bulb to help expel semen.
- Corpus spongiosum - pressurizes and constricts the urethra lumen to allow forceful
expulsion of semen.
- Glans - acts as a cushion to lessen the impact of the penis on female organs and provides sensory input
to facilitate erection.