A
lot of people think semen is produced entirely in the testicles, is
stored there, and at ejaculation, gets "pumped" from the
testicles out through the penis.This view is entirely too simple -different
components of semen are produced in several parts of the male reproductive
system, which work together before and during ejaculation.
Sperm
cells, which are of course the most important component of semen reproduction-wise
— are produced in the testicles (testes) in a process known
as spermatogenesis. Partially mature sperm cells are
constantly
moving into a structure called the epididymis, which secretes a fluid
that helps the sperm cells to finish maturing. Once fully mature,
sperm enter the vas deferens, a tube about 18 inches long that loops
over the bladder. (The vas deferens is cut and tied off in the birth-control
operation called a vasectomy.) Each vas deferens ends in an expanded
segment called the ampulla; this is where sperm is stored before each
ejaculation.
At
the base of the bladder are structures called the seminal
vesicles; these join with the ampulla of the vas deferens
to form the "ejaculatory duct." The seminal vesicles secrete
a thick liquid rich in sugar (specifically, fructose — commonly
found in fresh fruit), which is an important nutrient for the sperm
cells. In fact, the seminal vesicles are where most of the non-sperm
portion of semen is made.
The
prostate is a donut-shaped organ under the bladder;
it surrounds the prostatic urethra and secretes an alkaline (
basic)
fluid that accounts for up to a third of the non-sperm portion of
semen.
Finally,
the Cowper's glands, also known as bulbourethral
glands, are small structures near the base of the penis; their function
is to secrete mucus that lubricates and readies the urethra prior
to ejaculation. Most guys know this secretion as "pre-cum."
(The liquid is secreted upon sexual stimulation, not just during ejaculation.
Upon prolonged sexual stimulation the amount of pre-cum can sometimes
surpass the total amount of semen.) .
| Contributing
gland |
Percentage
of whole ejaculate |
| Testicles
and epididymes |
5
per cent |
| Seminal
vesicles |
46
to 80 per cent |
| Prostate
gland |
13
to 33 per cent |
| Bulbourethral
and urethral glands |
2
to 5 per cent |