In understanding male reproductive anatomy we have the advantage that many of the key organs are external to the body and in plain sight. In women the female reproductive anatomy in most of the key organs are internal. Looking at the figure below you can see the major components of the male reproductive system.
The testis is the organ in men where sperm are produced and where testosterone, the primary male sex hormone is produced. The testes are located in a sac that hangs from the outside of the males body between the base of the penis and the anus. This area in both men and women is called the perineum. The testes are outside the body because the production of sperm, called spermatogenesis, functions best when the temperature of the testes is slightly lower than the temperature of the rest of the body. By being outside the main structure of the body the testes remain somewhat cooler. You may notice that in cold weather the muscles of the scrotum contract drawing the testes up close to the body, and when it is warm the muscles relax allowing the testes to hand lower away from the body.
Inside the testis are millions of tiny tubules that sperm are released into in an immature state. The immature sperm travel through these tiny tubules which join together like the branches of a tree to become bigger and bigger until they come to an organ on the back of the testis called the epididymis. In the epididymis the tubules further come together until out of the bottom of the epididymis comes a single muscular tube called the vas deferens. The vas deferens then travels up through the scrotum, through a canal in the groin called the inguinal canal inside the body. Sperm are stored in a pouch off the vas deferens called the seminal vesicle for a few weeks while they mature. Then when a male ejaculates the seminal vesicles and vas deferens contract rhythmically and eject the sperm, diluted in fluids produced by the prostate and seminal vesicles through the tube in the penis called the urethra and out the tip of the urethral meatus (opening at the tip of the penis).
The penis is the organ that allows the male to deposit the sperm into the female’s vagina. The penis is made up of special tissue that has the capacity to fill with blood and become larger and firmer, called tumescence or an erection. There are three major parts to the penis. On each side are the corpora cavernosum (corpus means body, corpora is pleural), whose primary function is to facilitate erections. They become filled with blood with sexual excitement when the outflow of blood from these areas is constricted, and provide much of the rigidity and size increase of the erect penis. The corpus spongiosum is the central part of the penis that contains the urethra and enlarges at the tip to form the glans, or “head” of the penis. This also becomes engorged with an erection, but is less rigid, and tends to be the part of the penis with the most sensation.
The prostate is an organ inside the male that the urethra passes through and lies between the bladder and the penis. It also lies just in front of the rectum. It serves primarily to provide fluids for the sperm to be diluted into. This fluid, sperm, and the fluids combined is called semen, or seminal fluid.
Boys often wonder about their genitalia. Every person looks somewhat different. Their noses, ears, hands, feet, hair etc are all somewhat different. This variability is also seen in the genitalia. One of the biggest concerns of many boys and young men is the size of their penis. There is variability in size of the penis from one person to another, with most studies showing an average length of the erect penis of about 6 inches, with 95% of adults men between 4.2 and 7.5 inches measured on the top of the erect penis from the pubic bone to the tip of the glans. In addition the shape of the erect penis can vary somewhat from one individual to another. Minor curvature of the erect penis, either to one side or the other, or often curvature upwards is common and is of no concern. Overall size of the penis measured in the erect penis from the pubic bone to the tip of the glans is between 4-10 inches in the vast majority of adult men. None of these variations is a problem in the function of the penis as a sex organ.
Another concern for some boys is the size of the testes. This also varies considerably from individual to individual. The size of the testes bears no relationship to fertility, sexual function, or sex drive, and is really does not need to be a concern. Sometimes an illness or injury to a testis can leave one testis much smaller than the other. As long as one testis functions normally there is usually no concern about fertility or sexual function.
The amount of body hair including hair around the genitaila of both men and women varies considerably from individual to individual. It is largely a hereditary issues, much like hair color, eye color and other distinguishing personal features. It bears no relationship to fertility or sexual function. This is a commonly confused fact about sex education.
Circumcision is another issue that concerns some boys. In the United States more than half of babies are circumcised, whereas in Europe and much of the rest of the world few babies are circumcised except in Jewish families. Circumcision does not affect sexual function or fertility, and is a personal family choice.