Human Penis Anatomy

Definitions - The Corpus Cavernosum (CC) is one of a
pair of sponge-like regions of erectile tissue which
contain most of the blood in the penis during erection.
This is homologous to the corpus cavernosum clitoris in
the female; the body of the penis contains erectile tissue
in a pair of corpora cavernosum (literally "cave-like
bodies"), with a recognizably similar structure.

Tunica Albuginea (TA) aka as the white tunica is the
fibrous envelope of the corpora cavernosum penis. It
consists of approximately 5% elastin.  The majority of
the remaining tissue is collagen.

When a man becomes sexually excited the nerves
surrounding his penis cause the muscles around the arteries
to relax and more blood flows to the penis. The sponge-like
material (Corpus Cavernosum) absorbs and holds the
additional blood which causes the penis to become hard and
erect.  The TA is directly involved in achieving and
maintaining an erection. As the penis changes from a flaccid
state to an erect state, the TA thins from 2 mm to 0.25-0.5
mm, stiffens, and loses elasticity. The expansion and
stiffness of the TA puts pressure on the dorsal vein, impedes
venous return and is responsible for maintaining penile
hardness during male erection.

After ejaculation, the brain signals the penis to allow the
blood to leave and the penis then returns to the flaccid state.

Take particular note of the Corpus Cavernosum (CC) and
Tunica Albugina (TA) as they are affected by our disease.
Human Penis, Anatomy