All living things reproduce. Reproduction — the process by which organisms
make more organisms like themselves — is one of the things that set living things
apart from nonliving matter. 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 (pronounced: GAH-meetz), 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 children
are what make children similar to others in their family, but they are 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.
What Is 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 duct system, which is made up of the epididymis and the vas deferens
the accessory glands, which include the seminal vesicles and prostate gland
In a guy who's reached sexual maturity, the two testicles (pronounced:
TESS-tih-kulz), or testes (pronounced: TESS-teez), 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 (pronounced: tess-TOSS-tuh-rone). Testosterone
is a major part of puberty in guys, and as a guy makes his way through puberty, his
testicles produce more and more of it. Testosterone is the hormone that causes guys
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 (pronounced: ep-uh-DID-uh-miss)
and the vas deferens (pronounced: VAS DEF-uh-runz), 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 (pronounced: SEE-mun). 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
(pronounced: yoo-REE-thruh), 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 have a circumcision, 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.
Penises work the same, whether they are circumcised or not.
What Does the Male Reproductive System Do?
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
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 9 and 15, the pituitary (pronounced: pih-TOO-uh-ter-ee)
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.
Once a guy has reached puberty, he 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 (pronounced: sem-uh-NIF-er-iss TOO-byoolz). 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 (pronounced: ZY-goat)
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
Problems Affecting the Male Reproductive System
Guys may sometimes experience reproductive system problems. Below are some examples
of disorders that affect the male reproductive system:
Disorders of the Scrotum, Testicles, or Epididymis
Conditions affecting the scrotal contents may involve the testicles, epididymis,
or the scrotum itself.
injury. 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.
(pronounced: TOR-shen), when one of the testicles twists around, cutting off its blood
supply, can also happen to some guys. It's a serious problem that needs medical attention,
but luckily it's not common.
(pronounced: VAR-uh-koh-seal). This is a varicose vein (an abnormally swollen vein)
in the network of veins that run from the testicles. Varicoceles commonly develop
while a guy is going through puberty. A varicocele is usually not harmful, although
in some people it may damage the testicle or decrease sperm production, so it helps
for a guy to see his doctor if he's 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. All guys should do testicular
self-examinations regularly to help with early detection.
Epididymitis (pronounced: ep-uh-did-uh-MY-tuss) 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 (pronounced: HY-druh-seel) is 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.
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 (pronounced:
IN-gwuh-nul) 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 the following:
Inflammation of the penis. Symptoms of penile inflammation include
redness, itching, swelling, and pain. Balanitis is when the glans (the head of the
penis) becomes inflamed. Posthitis is foreskin inflammation, which is usually due
to a yeast or bacterial infection.
Hypospadius is a disorder in which the urethra opens on the underside
of the penis, not at the tip.
If you think you have symptoms of a problem with your reproductive system or if
you have questions about your growth and development, talk to your parent or doctor
— many problems with the male reproductive system can be treated.