The most-visited site
devoted to children's
health and development

Male Reproductive System


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 baby. Both the male and female reproductive systems are essential for reproduction.

Humans 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



  • the testicles
  • 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.




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 done during a baby boy's first few days of life. Although circumcision is not medically necessary, parents who choose to have their sons 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


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 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:

  • Next, the penis becomes longer and the seminal vesicles and prostate gland grow.
  • Hair begins to grow in the pubic area and later on the face and underarms. During this time, a boy's voice also deepens.
  • Boys also have a growth spurt during puberty as they reach their adult height and weight.




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.


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

  • Testicular trauma. Even a mild injury to the testicles can cause severe pain, bruising, or swelling. Most testicular injuries happen when the testicles are struck, hit, kicked, or crushed, usually during sports or other trauma. Testicular torsion, when one of the testicles twists around, cutting off its blood supply, is also a medical emergency that, thankfully, is 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 often develop while a boy is going through puberty. A varicocele is usually not harmful, but 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.
  • Hydrocele. A hydrocele is when fluid collects in the membranes surrounding the testes. Hydroceles may cause swelling in the scrotum around the testicle but are usually 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 is treated 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 is when the glans (the head of the penis) becomes inflamed. Posthitis is foreskin inflammation, usually due to a yeast or bacterial infection.
  • Hypospadias. In this disorder, 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 boys. It usually eases without treatment. If it interferes with urination, circumcision (removal of the foreskin) might be recommended.
  • Paraphimosis. This may develop when the foreskin of a boy's uncircumcised penis is retracted (pulled down to expose the glans) and becomes trapped so it can't be returned to the unretracted position. As a result, blood flow to the head of the penis can be affected, and a boy may have 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 might be recommended.
  • Ambiguous genitalia. This is 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, talk with your doctor — many problems with the male reproductive system can be treated. The doctor is also a good resource for your son if he has questions about growth and sexual development.

Reviewed by: Steven Dowshen, MD
Date reviewed: October 2015


© 1995- The Nemours Foundation. All rights reserved.
