The prostate is a walnut-shaped gland that is part of a man’s sex organs, which also include the penis, scrotum, and testicles. The prostate makes fluid that goes into semen, which is a mix of sperm and prostate fluid. Prostate fluid is important for a man’s ability to father children.

The prostate is in front of the rectum and just below the bladder. The gland surrounds the urethra at the neck of the bladder. The bladder neck is the area where the urethra joins the bladder. The urethra is the tube that carries urine from the bladder to the outside of the body. In men, the urethra also carries semen out through the penis during sexual climax, or ejaculation. The bladder and urethra are parts of the lower urinary tract.

Urine and semen flowing through the urethra pass through the prostate.


The prostate is a walnut-shaped gland that is part of a man’s sex organs, which also include the penis, scrotum, and testicles. The bladder and urethra are parts of the lower urinary tract.

The prostate gland is found only in males and is an essential part of the male reproductive system. It's about the size and shape of a walnut or a small plum in young men. In older men it normally grows to about the size of a lemon. It fits snugly into its position, sitting about 2 inches above the perineum, the muscular area between the scrotum and anus. The prostate's tissue is both glandular and nonglandular. It is made up of thousands of tiny fluid-producing glands interspersed with blood vessels, within a fibromuscular framework.

The urethra, the tube that carries both urine and semen, runs through the prostate gland, and is joined at about the center of the gland by the two seminal ducts. The seminal vesicles sit near the top, rear part of the prostate. The vas deferens, a long tube, connects the urethra with the testes.

The anatomy of the prostate gland can be described in two different ways, by lobe or by zone. Classification by lobe is more common in anatomy, and classification by zone is more common in pathology.

Lobes of the Prostate

• Anterior lobe. The front portion of the gland, lying in front of the urethra, composed entirely of muscle tissue. (Roughly corresponds to part of the transition zone.)
• Median lobe. The cone-shaped portion of the gland that sits between the two ejaculatory ducts and the urethra. (Roughly corresponds to part of the central zone.)
• Lateral lobes. The two lateral (right and left) lobes are separated by the urethra and form the main mass of the prostate. (The lateral lobes span all zones.)
• Posterior lobe. A term sometimes used to describe the rear part of the lateral lobes, which can be palpated through the rectum during a digital rectal exam (DRE). (Roughly corresponds to the peripheral zone.)

Zones of the Prostate

• Anterior zone. Located in the front of the prostate, this zone is composed mostly of muscle tissue.
• Transition zone. The innermost part of the gland; surrounds the urethra where it passes through the prostate. This is the part of the gland, along with the central zone, that begins to enlarge after the age of 40.
• The central zone. Surrounds the transition zone.
• The peripheral zone. Located in the back of the prostate gland. About 70-75% of prostate cancer occurs here.

The Prostate Capsule

The prostate capsule is a fibrous membrane that encapsulates the prostate. Extracapsular extension refers to prostate cancer that has spread outside of the prostate capsule and into the surrounding tissues and organs.

The Prostate Gland

The prostate gland is the largest of the male reproductive glands and serves a vital function in the male reproductive system. It secretes a thin, milky-white liquid called prostatic fluid that is rich in zinc, citric acid, choline, and various proteins and hormones. Prostatic fluid contributes about 30% of the volume of seminal fluid. The various components of the prostatic fluid aid the sperm by providing a protective medium for them to move in as they make their way through the vagina. Without this protective medium, most sperm would die soon after ejaculation.

One of the chemicals in prostatic fluid is prostate specific antigen (PSA). PSA is an enzyme (a catalyst that causes biochemical reactions). During ejaculation, the muscular portion of the prostate contracts and pushes the prostatic fluid through tiny ducts into the urethra, where it mixes with other elements of seminal fluid. The muscular contractions of the prostate help to expel semen during ejaculation.

What Is Semen?

Semen has two main components: sperm and seminal plasma. Seminal plasma is a complex fluid that nurtures and protects the sperm and helps to ensure they pass unharmed through the vagina and into the uterus.

Semen is produced through a complex series of steps and by a number of organs, ducts, and glands:

• Testes. Sperm and testosterone are made in the testes, which are composed of tightly coiled structures called seminiferous tubules. Certain cells inside the testes act like nurseries, nurturing the immature sperm until they reach maturity and are released into the seminiferous tubules.
• Epididymis. Located on top of the testes, the epididymis is a tightly coiled tube where sperm are stored for up to 2 weeks while they mature, develop motility, and become capable of fertilization.
• Vas deferens. The vas deferens is a long curving tube that transports sperm from the epididymis to the seminal vesicle. It acts as a storage site for sperm until ejaculation. The entire process of sperm maturation takes about 74 days.
• Ejaculatory ducts. The vas deferens and the ducts of the seminal vesicles join together to form the ejaculatory ducts. They descend through the prostate gland and into the urethra.
• Seminal vesicles. The seminal vesicles supply a viscous, alkaline secretion that forms about 60% of the semen. The fluid from the seminal vesicles is rich in nutrients to provide energy for sperm metabolism and to increase sperm motility. It also contains a substance that causes the semen to clot after ejaculation, thought to be useful for keeping the semen at the neck of the uterus.
• Prostate gland. The prostate gland discharges prostatic fluid into the urethra during ejaculation. The prostate's muscular contractions help to propel the seminal fluid through the urethra and out of the penis. Once inside a woman's vagina, the PSA in the prostatic fluid liquifies the semen that has been clotted by the seminal fluid, so that the sperm can swim off to fertilize the ovum (egg).
• Bulbourethral (Cowper's) glands. The bulbourethral glands, sometimes known as the Cowper's glands, are two pea-sized glands found just under the prostate. They produce the thick, clear, pre-ejaculate fluid that acts as a lubricant and may clear out the urethra in preparation for ejaculation.
• Urethra. The urethra discharges both urine and semen. During male orgasm and ejaculation, the muscular sphincter at the neck of the bladder closes, preventing urine from entering the urethra.

What Happens During Ejaculation?

During male orgasm and ejaculation, sperm travel upwards through the vas deferens and then down into the upper portion of the prostate. The sperm and fluid from the seminal vesicles then mix with prostatic fluid and fluid from the bulbourethral glands to form the semen. The ejaculate, now containing sperm and fluids from the seminal vesicles, prostate, and bulbourethral glands, flows from the ejaculatory ducts into the urethra. From the urethra it passes out through the end of the penis.

Sperm are immobile at body temperature; therefore, the testes are external to the body so that a correct temperature is maintained for motility. In land mammals, including humans, the pair of testes must be suspended outside the body so the environment of the sperm is about 2 °C lower than body temperature to produce viable sperm. If the testes do not descend through the abdominal cavity during fetal development, the individual has reduced fertility.

The scrotum houses the testicles or testes (singular: testis), and provides passage for blood vessels, nerves, and muscles related to testicular function. The testes are a pair of male gonads that produce sperm and reproductive hormones. Each testis is approximately 2.5 by 3.8 cm (1.5 by 1 inch) in size and divided into wedge-shaped lobes by septa. Coiled in each wedge are seminiferous tubules that produce sperm.

The penis drains urine from the urinary bladder and is a copulatory organ during intercourse (Figure 18.12; Table 18.1). The penis contains three tubes of erectile tissue that become engorged with blood, making the penis erect, in preparation for intercourse. The organ is inserted into the vagina culminating with an ejaculation. During orgasm, the accessory organs and glands connected to the testes contract and empty the semen (containing sperm) into the urethra and the fluid is expelled from the body by muscular contractions causing ejaculation. After intercourse, the blood drains from the erectile tissue and the penis becomes flaccid.

Semen is a mixture of sperm (about five percent of the total) and fluids from accessory glands that contribute most of the semen’s volume. Sperm are haploid cells, consisting of a flagellum for motility, a neck that contains the cell’s energy-producing mitochondria, and a head that contains the genetic material (Figure 18.11). An acrosome (acrosomal vesicle) is found at the top of the head of the sperm. This structure contains enzymes that can digest the protective coverings that surround the egg and allow the sperm to fuse with the egg. An ejaculate will contain from two to five milliliters of fluid and from 50–120 million sperm per milliliter.

Figure 18.11 As seen in this scanning electron micrograph, human sperm has a flagellum, neck, and head. (credit: scale-bar data from Matt Russell)

Sperm form in the walls of seminiferous tubules that are coiled inside the testes (Figure 18.12; Table 18.1). The walls of the seminiferous tubules are made up of the developing sperm cells, with the least developed sperm at the periphery of the tubule and the fully developed sperm next to the lumen. The sperm cells are associated with Sertoli cells that nourish and promote the development of the sperm. Other cells present between the walls of the tubules are the interstitial cells of Leydig, which produce testosterone once the male reaches adolescence.

When the sperm have developed flagella they leave the seminiferous tubules and enter the epididymis (Figure 18.12; Table 18.1). This structure lies along the top and posterior of the testes and is the site of sperm maturation. The sperm leave the epididymis and enter the vas deferens, which carries the sperm behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles. During a vasectomy, a section of the vas deferens is removed, preventing sperm (but not the secretions of the accessory glands) from being passed out of the body during ejaculation and preventing fertilization.

The bulk of the semen comes from the accessory glands associated with the male reproductive system. These are the seminal vesicles, the prostate gland, and the bulbourethral gland (Figure 18.12; Table 18.1). The secretions from the accessory glands provide important compounds for the sperm including nutrients, electrolytes, and pH buffering. There are also coagulation factors that affect sperm delivery and motility.

VISUAL CONNECTION

Figure 18.12 The reproductive structures of the human male are shown.

Male Reproductive Anatomy

Table18.1

Sperm Transport

To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.

Role of the Epididymis

From the lumen of the seminiferous tubules, the immotile sperm are surrounded by testicular fluid and moved to the epididymis (plural = epididymides), a coiled tube attached to the testis where newly formed sperm continue to mature. Though the epididymis does not take up much room in its tightly coiled state, it would be approximately 6 m (20 feet) long if straightened. It takes an average of 12 days for sperm to move through the coils of the epididymis, with the shortest recorded transit time in humans being one day. Sperm enter the head of the epididymis and are moved along predominantly by the contraction of smooth muscles lining the epididymal tubes. As they are moved along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use this ability to move independently toward the unfertilized egg. The more mature sperm are then stored in the tail of the epididymis (the final section) until ejaculation occurs.

Duct System

During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens (also called the vas deferens). The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord. Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt sperm delivery can be performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is called a vasectomy, and it is an effective form of male birth control. Although it may be possible to reverse a vasectomy, clinicians consider the procedure permanent, and advise men to undergo it only if they are certain they no longer wish to father children.

From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the abdominal wall. From here, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder where it dilates in a region called the ampulla (meaning “flask”).

Sperm make up only 5 percent of the final volume of semen, the thick, milky fluid that the male ejaculates. The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands.

Seminal Vesicles

As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle. The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume. Seminal vesicle fluid contains large amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female reproductive tract.

The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct, a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.

Prostate Gland

As shown in Figure, the centrally located prostate gland sits anterior to the rectum at the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, the prostate is formed of both muscular and glandular tissues. It excretes an alkaline, milky fluid to the passing seminal fluid—now called semen—that is critical to first coagulate and then decoagulate the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing time for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm can then pass farther into the female reproductive tract.

The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again. This enlargement does not usually cause problems; however, abnormal growth of the prostate, or benign prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a sensation that the bladder has not emptied completely. By age 60, approximately 40 percent of men have some degree of BPH. By age 80, the number of affected individuals has jumped to as many as 80 percent. Treatments for BPH attempt to relieve the pressure on the urethra so that urine can flow more normally. Mild to moderate symptoms are treated with medication, whereas severe enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.

Another common disorder involving the prostate is prostate cancer. According to the Centers for Disease Control and Prevention (CDC), prostate cancer is the second most common cancer in men. However, some forms of prostate cancer grow very slowly and thus may not ever require treatment. Aggressive forms of prostate cancer, in contrast, involve metastasis to vulnerable organs like the lungs and brain. There is no link between BPH and prostate cancer, but the symptoms are similar. Prostate cancer is detected by a medical history, a blood test, and a rectal exam that allows physicians to palpate the prostate and check for unusual masses. If a mass is detected, the cancer diagnosis is confirmed by biopsy of the cells.

Bulbourethral Glands

The final addition to semen is made by two bulbourethral glands (or Cowper’s glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to clean urine residues from the penile urethra. The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly before the release of the semen. It is therefore sometimes called pre-ejaculate. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy.

Stan's Story

Stan just found out that a friend has prostate cancer. Many men he knows have prostate problems. He’s worried that this might happen to him.

It’s true that prostate problems are common after age 50. The good news is there are many things you can do.

What Is the Prostate?

The prostate is a small gland in men that helps make semen. Located just below the bladder in front of the rectum, it wraps around the tube that carries urine and semen out of the body. It tends to grow larger as you get older. If your prostate gets too large, it can cause a number of health issues.

Common Problems

Here are some examples of non-cancer prostate problems:

Benign prostatic hyperplasia, or BPH, is very common in older men. It means your prostate is enlarged but not cancerous. Treatments for BPH include:

• Watchful waiting, also called active surveillance. If your symptoms are not too bad, your doctor may tell you to wait to see if they get worse before starting treatment. Your doctor will tell you how often to return for checkups.
• Medications. Medicines can help shrink the prostate or relax muscles near your prostate to ease symptoms.
• Surgery. If nothing else has worked, your doctor may suggest surgery to help urine flow.
• Other treatments. Sometimes radio waves, microwaves, or lasers are used to treat urinary problems caused by BPH. These methods use different kinds of heat to reduce extra prostate tissue.

Acute bacterial prostatitis usually starts suddenly from a bacterial infection. See your doctor right away if you have fever, chills, or pain in addition to prostate symptoms. Most cases can be cured with antibiotics. You also may need medication to help with pain or discomfort.

Chronic bacterial prostatitis is an infection that comes back again and again. This rare problem can be hard to treat. Sometimes, taking antibiotics for a long time may work. Talk with your doctor about other things you can do to help you feel better.

Chronic prostatitis, also called chronic pelvic pain syndrome, is a common prostate problem. It can cause pain in the lower back, in the groin, or at the tip of the penis. Treatment may require a combination of medicines, surgery, and lifestyle changes.

Be sure to talk with your doctor about the possible side effects of treatment.

Symptoms of Prostate Problems

See your doctor right away if you have any of these symptoms:

• Frequent urge to urinate
• Need to get up many times during the night to urinate
• Blood in urine or semen
• Pain or burning urination
• Painful ejaculation
• Frequent pain or stiffness in lower back, hips, pelvic or rectal area, or upper thighs
• Dribbling of urine

Prostate Cancer

Prostate cancer is common among American men. Your chance of getting prostate cancer may be affected by your:

• Age. Men age 50 and older run a greater risk.
• Race. Prostate cancer is most common among African-American men, followed by Hispanic and Native-American men. Asian-American men have the lowest rates of prostate cancer.
• Family history. If your father or brother had prostate cancer, you are more likely to have it, too.
• Diet. The risk of prostate cancer may be higher for men who eat high-fat diets.

Diagnosing Prostate Cancer

To find out if prostate symptoms are caused by cancer, your doctor will ask about your past medical problems and your family’s medical history. Your doctor also will perform a physical exam. During the exam, your doctor will put a gloved finger into your rectum to examine your prostate to check for:

• The size, firmness, and texture of the prostate
• Any hard areas, lumps, or growth spreading beyond the prostate
• Any pain caused by touching or pressing on the prostate

You may be asked to give a urine sample for testing. Your doctor also may do a blood test to check the prostate-specific antigen (PSA) level. PSA levels can be high in men with an enlarged prostate gland or with prostate cancer. You may also need an ultrasound exam that takes computer pictures of the prostate.

If tests show that you might have cancer, your doctor will refer you to a specialist (a urologist) for a prostate biopsy. The doctor will take small tissue samples from several areas of the prostate gland to look for cancer cells.

Treating Prostate Cancer

Treatment for prostate cancer depends on whether cancer is in part or all of the prostate, or if it has spread to other parts of the body. It also depends on your age and overall health. Talk with your doctor about the best treatment choice for you and the possible side effects of treatment. You may want to ask another doctor for a second opinion.

Treatment for prostate cancer may be:

• Watchful waiting, also called active surveillance. If the cancer is not causing problems, you may decide not to get treated right away. Instead, your doctor will check regularly for changes in your condition. Treatment will start if the cancer begins to grow.
• Surgery. The most common type of surgery removes the whole prostate and some nearby tissue.
• Radiation therapy. This treatment uses radiation to kill cancer cells and shrink tumors. The radiation may come from an x-ray machine or from tiny radioactive pellets placed inside or near the tumor.
• Hormone therapy. Men having other treatments, like radiation therapy, also may be treated with drugs to stop the body from making testosterone. This is done if it seems likely that the cancer will come back. Hormone therapy also can be used for prostate cancer that has spread beyond the prostate.

PSA Testing

Until recently, many doctors encouraged yearly PSA testing for all men beginning at age 50, or even earlier for men at high risk of prostate cancer. As doctors have learned more about the benefits and harms of prostate cancer screening, they have begun to caution against annual PSA testing. Talk with your doctor about what is best for you.

Yearly PSA testing in men without symptoms is generally not recommended. However, in men who report prostate symptoms, PSA testing (along with digital rectal examination) can help doctors determine the nature of the problem. In men who have been treated for prostate cancer, the PSA test may be used to see if the cancer has come back.