The Male Reproductive System
As is very evident, the male reproductive system including the ‘fun stuff’ is located primarily on the outside of the body with the penis and scrotum being the most visible. The penis has received a lot of attention in art, literature, and mythology with a phallic symbol equating to virility, power, and prosperity. These connections with power and virility have led to a lot of misconceptions and, for some, unnecessary disappointment.
The penis is a tube-shaped organ consisting of a root, body, and extremity known as the glans penis or head. The root of the penis is connected to the pelvis by strong ligaments. The body of the penis consists of three cylinders containing tissue that can become erect. No, there is no bone in the penis in spite of alleged X-rays depicting a broken bone in a supposedly fractured penis!
No, there is no bone in the penis!
This X-ray was taken using a broken chicken bone on top of the penis.
The glans penis is the sensitive area. It contains a rich supply of sensory nerves that contribute to the man’s sexual response. While the shaft of the penis can be sensitive, it is nowhere nearly as sensitive as the head of the penis. The most sensitive area is around the crown or ridge of the head. The glans also contains the opening to the urethra through which urine and sperm are expelled from the body.
The scrotum, a pouch located beneath the penis is the other visible component of the male reproductive system and contains the testes. When allowed to hang free, the left side of the scrotum is larger than the right because the spermatic cord of the left is longer. The skin of the scrotum has a large number of blood vessels that, when injured, can bleed heavily.
Another layer of the scrotum located under the skin is not only highly vascular, but has a strong ability to contract. Since the testes need to be cooler than the rest of the body in order to produce sperm, the ability of the tissue to contract and expand is important. For example, when the scrotum is exposed to cold, this layer contracts bringing the testes closer to the body for warmth. This phenomenon is commonly referred to as ‘shrinkage.’ In contrast, when the temperature is warm, this layer relaxes and the testes are allowed to hang away from the body.
Inside the scrotum, suspended by the spermatic cords are the testes. These oval-shaped organs are responsible for producing sperm and male hormone, testosterone. Each testis contains a large number of blood vessels and nerve endings. Injury to the testes can cause bleeding and a tremendous amount of pain (as any man who has been hit or kicked in the groin can attest).
Sperm are produced in tiny, coiled tubes and are transported to a flattened area called the epididymis that runs along the back edge of each testis. The epididymis consists of 18 to 20 feet of convoluted tubes that temporarily store the sperm. When the sperm initially arrive at the epididymis, they are immature and cannot swim on their own nor are they able to fertilize an egg.
From the epididymis, sperm are transported to a tube called the vas deferens and eventually arrive at an area next to the urinary bladder where the sperm are stored prior to ejaculation. During a vasectomy, the vas deferens is cut and a piece is removed to prevent sperm from leaving the epididymis. This procedure renders a man sterile. Note, however, that until the vas deferens has been depleted of stored sperm, pregnancy can still occur. After a vasectomy continue to use birth control until the semen has been cleared of any sperm. Checking for sperm is usually done in a doctor’s office or lab several weeks after the vasectomy. It is important to keep that appointment and to take a sample of semen with you or be prepared to use the office’s restroom.
Some men are concerned that having a vasectomy will reduce the amount of ejaculate they produce. While the volume is smaller, it is reduced by an almost unnoticed amount. Most of the ejaculate is not sperm, rather, it is fluid produced by other structures in the reproductive system, specifically the seminal vesicles and prostate that make up the bulk of the ejaculate.
The two seminal vesicles are located on either side of the urinary bladder between the bladder’s base and rectum. The seminar vesicles were originally thought to store sperm; however, recent information indicates that the seminal vesicles are glands of secretion. The seminal vesicles secrete a mucus material that contains nutrients for the sperm as well as fibrinogen – something that will cause the semen to ‘clot.’ When a man ejaculates, the sperm enter the ejaculatory duct and are immediately followed by seminal fluid. It is this fluid that makes up most of the ejaculate.
The prostate gland is a chestnut-shaped gland located just below the urinary bladder, surrounding the urethra. This gland secrets a thin, milky fluid that is alkaline in nature. Prostate fluid includes citric acid, calcium, acid phosphate, and a clotting enzyme. The function of the fluid is to reduce the acidity of the semen and vaginal secretions, enhancing the sperm’s fertility and motility. During ejaculation, the prostate contracts and adds its fluid to the semen as it passes into the urethra. Once ejaculated, the clotting enzyme from the prostate and fibrinogen from the seminal vesicles combine to coagulate the semen. This coagulation keeps it from immediately dripping out of the vagina. The gelatinized semen dissolves within 15 to 20 minutes after which the sperm become highly motile.
The Cowper’s glands (also known as bulbourethral glands) are tiny glands located at the base of the urethra that secretes a fluid that acts to lubricate the urethra. During sexual stimulation, these glands can secrete copious amounts of fluid that is often referred to as ‘pre-cum.’ Some men have been embarrassed when this fluid seeps through their clothing and wets the front of their pants.
Sexual Arousal and Ejaculation
Men become aroused by visual, physical, and psychological stimulation. Physical stimulation on the glans of the penis sends nerve signals to the spinal cord that ultimately causes an erection. Since an erection is a reflex, the brain doesn’t have to be involved in sexual excitement. This, unfortunately, has led to many jokes about a man, his brain, and his penis.
When sexual stimulation occurs, the arteries of the penis open or dilate and flood the penis with blood. As these arteries engorge they compress or constrict the nearby veins, restricting blood flow out of the penis. The corpus cavernosum is increasingly filled with blood and the penis becomes erect. With continued sexual stimulation, the Cowper’s glands secrete their lubricating fluid.
As the stimulation becomes intense, the nervous system sends out emission and ejaculation impulses from the spinal cord. Emission begins with the contraction of the vas deferens and epididymis followed by the muscular contractions of the seminal vesicles and prostate gland. Ejaculation occurs when the urethra fills with semen sending a signal to the spinal cord to cause rhythmic muscular contractions at the base of the penis. These contractions expel sperm, seminal fluid, and prostate fluid from the urethra. It should be noted that when a man is aroused and erect the bladder is prevented from emptying, thus a man is unable to urinate. This actually protects the sperm since urine can damage sperm cells.