All living things reproduce. Reproduction - the process by which
organisms make more organisms like themselves - is one of the
things that sets living things apart from nonliving things. But
even though the reproductive system is essential to keeping a
species alive, unlike other body systems it's not essential to
keeping an individual alive.
In the human reproductive process, two kinds of
sex cells
, or
gametes
, are involved. The male gamete, or
sperm
, and the female gamete, the
egg
or
ovum
, meet in the female's reproductive system to create a new
individual. Both the male and
female reproductive systems
are essential for reproduction.
Humans, like other organisms, pass certain characteristics of
themselves to the next generation through their
genes
, the special carriers of human traits. The genes parents pass
along to their offspring are what make kids similar to others in
their family, but they're also what make each child unique.
These genes come from the father's sperm and the mother's
egg, which are produced by the male and female reproductive
systems.
Understanding the male reproductive system, what it does, and
the problems that can affect it can help you better understand your
son's reproductive health.
About the Male Reproductive System
Most species have two sexes: male and female. Each sex has
its own unique reproductive system. They are different in shape and
structure, but both are specifically designed to produce, nourish,
and transport either the egg or sperm.
Unlike the female, whose sex organs are located entirely within
the pelvis, the male has reproductive organs, or
genitals
, that are both inside and outside the pelvis. The male genitals
include:
- the testicles
- the duct system, which is made up of the epididymis and the
vas deferens
- the accessory glands, which include the seminal vesicles and
prostate gland
- the penis
In a guy who has reached sexual maturity, the two
testicles
, or
testes
, produce and store millions of tiny sperm cells. The testicles are
oval-shaped and grow to be about 2 inches (5 centimeters) in length
and 1 inch (3 centimeters) in diameter. The testicles are also part
of the endocrine system because they produce hormones, including
testosterone
. Testosterone is a major part of puberty in boys, and as a guy
makes his way through puberty, his testicles produce more and more
of it. Testosterone is the hormone that causes boys to develop
deeper voices, bigger muscles, and body and facial hair, and it
also stimulates the production of sperm.
Alongside the testicles are the
epididymis
and the
vas deferens
, which make up the duct system of the male reproductive organs.
The vas deferens is a muscular tube that passes upward alongside
the testicles and transports the sperm-containing fluid called
semen
. The epididymis is a set of coiled tubes (one for each testicle)
that connects to the vas deferens.
The epididymis and the testicles hang in a pouch-like structure
outside the pelvis called the
scrotum
. This bag of skin helps to regulate the temperature of testicles,
which need to be kept cooler than body temperature to produce
sperm. The scrotum changes size to maintain the right temperature.
When the body is cold, the scrotum shrinks and becomes tighter to
hold in body heat. When it's warm, the scrotum becomes larger
and more floppy to get rid of extra heat. This happens without a
guy ever having to think about it. The brain and the nervous system
give the scrotum the cue to change size.
The
accessory glands
, including the seminal vesicles and the prostate gland, provide
fluids that lubricate the duct system and nourish the sperm. The
seminal vesicles
are sac-like structures attached to the vas deferens to the side of
the bladder. The
prostate gland
, which produces some of the parts of semen, surrounds the
ejaculatory ducts at the base of the
urethra
, just below the bladder. The urethra is the channel that carries
the semen to the outside of the body through the penis. The urethra
is also part of the urinary system because it is also the channel
through which urine passes as it leaves the bladder and exits the
body.
The
penis
is actually made up of two parts: the
shaft
and the
glans
. The shaft is the main part of the penis and the glans is the tip
(sometimes called the head). At the end of the glans is a small
slit or opening, which is where semen and urine exit the body
through the urethra. The inside of the penis is made of a spongy
tissue that can expand and contract.
All boys are born with a
foreskin
, a fold of skin at the end of the penis covering the glans. Some
boys are
circumcised
, which means that a doctor or clergy member cuts away the
foreskin. Circumcision is usually performed during a baby boy's
first few days of life. Although circumcision is not medically
necessary, parents who choose to have their children circumcised
often do so based on religious beliefs, concerns about hygiene, or
cultural or social reasons. Boys who have circumcised penises and
those who don't are no different: All penises work and feel the
same, regardless of whether the foreskin has been removed.
What the Male Reproductive System Does
The male sex organs work together to produce and release semen
into the reproductive system of the female during sexual
intercourse. The male reproductive system also produces sex
hormones, which help a boy develop into a sexually mature man
during
puberty
.
When a baby boy is born, he has all the parts of his
reproductive system in place, but it isn't until puberty that
he is able to reproduce. When puberty begins, usually between the
ages of 10 and 14, the
pituitary gland
- which is located near the brain - secretes hormones that
stimulate the testicles to produce testosterone. The production of
testosterone brings about many physical changes. Although the
timing of these changes is different for every guy, the stages of
puberty generally follow a set sequence.
- During the first stage of male puberty, the scrotum and
testes grow larger.
- Next, the penis becomes longer, and the seminal vesicles and
prostate gland grow.
- Hair begins to appear in the pubic area and later it grows on
the face and underarms. During this time, a male's voice also
deepens.
- Boys also undergo a
growth spurt
during puberty as they reach their adult height and weight.
A male who has reached puberty will produce millions of sperm
cells every day. Each sperm is extremely small: only 1/600 of an
inch (0.05 millimeters long). Sperm develop in the testicles within
a system of tiny tubes called the
seminiferous tubules
. At birth, these tubules contain simple round cells, but during
puberty, testosterone and other hormones cause these cells to
transform into sperm cells. The cells divide and change until they
have a head and short tail, like tadpoles. The head contains
genetic material (genes). The sperm use their tails to push
themselves into the epididymis, where they complete their
development. It takes sperm about 4 to 6 weeks to travel through
the epididymis.
The sperm then move to the vas deferens, or sperm duct. The
seminal vesicles and prostate gland produce a whitish fluid called
seminal fluid
, which mixes with sperm to form semen when a male is sexually
stimulated. The penis, which usually hangs limp, becomes hard when
a male is sexually excited. Tissues in the penis fill with blood
and it becomes stiff and erect (an erection). The rigidity of the
erect penis makes it easier to insert into the female's vagina
during sexual intercourse. When the erect penis is stimulated,
muscles around the reproductive organs contract and force the semen
through the duct system and urethra. Semen is pushed out of the
male's body through his urethra - this process is called
ejaculation
. Each time a guy ejaculates, it can contain up to 500 million
sperm.
When the male ejaculates during intercourse, semen is deposited
into the female's vagina. From the vagina the sperm make their
way up through the cervix and move through the uterus with help
from uterine contractions. If a mature egg is in one of the
female's fallopian tubes, a single sperm may penetrate it, and
fertilization
, or
conception
, occurs.
This fertilized egg is now called a
zygote
and contains 46 chromosomes - half from the egg and half from the
sperm. The genetic material from the male and female has combined
so that a new individual can be created. The zygote divides again
and again as it grows in the female's uterus, maturing over the
course of the pregnancy into an embryo, a fetus, and finally a
newborn baby.
Things That Can Go Wrong With the Male Reproductive System
Boys may sometimes experience reproductive system problems,
including:
Disorders of the Scrotum, Testicles, or Epididymis
Conditions affecting the scrotal contents may involve the
testicles, epididymis, or the scrotum itself.
-
Testicular trauma.
Even a mild injury to the testicles can cause severe pain,
bruising, or swelling. Most testicular injuries occur when the
testicles are struck, hit, kicked, or crushed, usually during
sports or due to other trauma. Testicular torsion, when one of
the testicles twists around, cutting off its blood supply, is
also a problem that some teen males experience, although it's
not common. Surgery is needed to untwist the cord and save the
testicle.
-
Varicocele.
This is a varicose vein (an abnormally swollen vein) in the
network of veins that run from the testicles. Varicoceles
commonly develop while a boy is going through puberty. A
varicocele is usually not harmful, although it can damage the
testicle or decrease sperm production. Take your son to see his
doctor if he is concerned about changes in his testicles.
-
Testicular cancer.
This is one of the most common cancers in men younger than
40. It occurs when cells in the testicle divide abnormally and
form a tumor. Testicular cancer can spread to other parts of the
body, but if it's detected early, the cure rate is excellent.
Teen boys should be encouraged to learn to perform testicular
self-examinations.
-
Epididymitis
is inflammation of the epididymis, the coiled tubes that connect
the testes with the vas deferens. It is usually caused by an
infection, such as the sexually transmitted disease chlamydia,
and results in pain and swelling next to one of the
testicles.
-
Hydrocele.
A hydrocele occurs when fluid collects in the membranes
surrounding the testes. Hydroceles may cause swelling in the
scrotum around the testicle but are generally painless. In
some cases, surgery may be needed to correct the condition.
-
Inguinal
hernia
. When a portion of the intestines pushes through an abnormal
opening or weakening of the abdominal wall and into the groin or
scrotum, it is known as an inguinal hernia. The hernia may look
like a bulge or swelling in the groin area. It can be corrected
with surgery.
Disorders of the Penis
Disorders affecting the penis include:
-
Inflammation of the penis.
Symptoms of penile inflammation include redness, itching,
swelling, and pain. Balanitis occurs when the glans (the head of
the penis) becomes inflamed. Posthitis is foreskin inflammation,
which is usually due to a yeast or bacterial infection.
-
Hypospadias.
This is a disorder in which the urethra opens on the underside of
the penis, not at the tip.
-
Phimosis.
This is a tightness of the foreskin of the penis and is common in
newborns and young children. It usually resolves itself without
treatment. If it interferes with urination, circumcision (removal
of the foreskin) may be recommended.
-
Paraphimosis.
This may develop when a boy's uncircumcised penis is
retracted but doesn't return to the unretracted position. As
a result, blood flow to the head of the penis may be impaired,
and your son may experience pain and swelling. A doctor may use
lubricant to make a small incision so the foreskin can be pulled
forward. If that doesn't work, circumcision may be
recommended.
-
Ambiguous genitalia.
This occurs when a child is born with genitals that aren't
clearly male or female. In most boys born with this disorder, the
penis may be very small or nonexistent, but testicular tissue is
present. In a small number of cases, the child may have both
testicular and ovarian tissue.
-
Micropenis.
This is a disorder in which the penis, although normally formed,
is well below the average size, as determined by standard
measurements.
If your son has symptoms of a problem with his reproductive
system or he has questions about growth and sexual development,
talk with your doctor - many problems with the male reproductive
system can be treated.
Reviewed by:
Steven Dowshen, MD
Date reviewed: November 2007
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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