14.5: Disorders of the Male Reproductive System - Biology

14.5: Disorders of the Male Reproductive System - Biology

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Offering to the Gods

The marble penis and scrotum depicted in Figure (PageIndex{1}) comes from ancient Rome, during the period from about 200 BCE to 400 CE. During that time, offerings like this were commonly given to the gods by people with health problems, either in the hopes of a cure or as thanks for receiving one. The offerings were generally made in the shape of the afflicted body part. Scholars think this marble penis and scrotum may have been an offering given in hopes of — or thanks for — a cure for impotence, known medically today as erectile dysfunction.

Erectile Dysfunction

Erectile dysfunction (ED) is sexual dysfunction characterized by the regular and repeated inability of a sexually mature individual to obtain or maintain an erection. It is a common disorder that affects about 40 percent of people with penises.

Causes of Erectile Dysfunction

The penis normally stiffens and becomes erect when the columns of spongy tissue within the shaft of the penis (the corpora cavernosa and corpus spongiosum) become engorged with blood. Anything that hampers normal blood flow to the penis may, therefore, interfere with its potential to fill with blood and become erect. The normal nervous control of sexual arousal or penile engorgement may also fail and lead to problems obtaining or maintaining an erection

Specific causes of ED include both physiological and psychological causes. Physiological causes include the use of therapeutic drugs (such as antidepressants), aging, kidney failure, diseases (such as diabetes or multiple sclerosis), tobacco smoking, and treatments for other disorders (such as prostate cancer). Psychological causes are less common but may include stress, performance anxiety, or mental disorders. The risk of ED may also be greater in people with obesity, cardiovascular disease, poor dietary habits, and overall poor physical health. Having an untreated hernia in the groin may also lead to ED.

Treatments for Erectile Dysfunction

Treatment of ED depends on its cause or contributing factors. For example, for tobacco smokers, smoking cessation may bring significant improvement in ED. Improving overall physical health by losing weight and exercising regularly may also be beneficial. The most common first-line treatment for ED, however, is the use of oral prescription drugs, known by brand names such as Viagra® and Cialis®. These drugs help ED by increasing blood flow to the penis. Other potential treatments include topical creams applied to the penis, injection of drugs into the penis, or the use of a vacuum pump that helps draw blood into the penis by applying negative pressure. More invasive approaches may be used as a last resort if other treatments fail. These usually involve surgery to implant inflatable tubes or rigid rods into the penis.

Ironically, the world’s most venomous spider —the Brazilian wandering spider (Figure (PageIndex{2})) — may offer a new treatment for ED. The venom of this spider is known to cause priapism in humans. Priapism is a prolonged erection that may damage the reproductive organs and lead to infertility if it continues too long. Researchers are investigating one of the components of the spider’s venom as a possible treatment for ED if taken in minute quantities.


Epididymitis is inflammation of the epididymis. The epididymis is one of the paired organs within the scrotum where sperms mature and are stored. Discomfort or pain and swelling in the scrotum are typical symptoms of epididymitis, which is a relatively common condition, especially in young individuals. In the U.S. alone, more than half a million cases of epididymitis are diagnosed annually between the ages of 18 to 35.

Acute vs. Chronic Epididymitis

Epididymitis may be acute or chronic. Acute diseases are generally short-term conditions, whereas chronic diseases may last years — or even lifelong.

Acute Epididymitis

Acute epididymitis generally has a fairly rapid onset and is most often caused by a bacterial infection. Bacteria in the urethra can back-flow through the urinary and reproductive structures to the epididymis. In sexually active individuals, many cases of acute epididymitis are caused by sexually transmitted bacteria. Besides pain and swelling, common symptoms of acute epididymitis include redness, warmth in the scrotum, and a fever. There may also be a urethral discharge.

Chronic Epididymitis

Chronic epididymitis is epididymitis that lasts for more than three months. In some, the condition may last for years. It may occur with or without a bacterial infection being diagnosed. Sometimes, it is associated with lower back pain that occurs after an activity that stresses the lower back, such as heavy lifting or a long period spent driving a vehicle.

Treatment of Epididymitis

If a bacterial infection is suspected, both acute and chronic epididymitis are generally treated with antibiotics. For chronic epididymitis, antibiotic treatment may be prescribed for as long as four to six weeks to ensure the complete eradication of any possible bacteria. Additional treatments often include anti-inflammatory drugs to reduce inflammation of the tissues and painkillers to control the pain, which may be severe. Physically supporting the scrotum and applying cold compresses may also be recommended to help relieve swelling and pain.

Regardless of symptoms, treatment is important for both acute and chronic epididymitis, because major complications may occur otherwise. Untreated acute epididymitis may lead to an abscess — which is a buildup of pus — or to the infection spreading to other organs. Untreated chronic epididymitis may lead to permanent damage to the epididymis and testis, and it may even cause infertility.

Male Reproductive Cancers

Why does the Brazilian hospital pictured in Figure (PageIndex{3}) have a huge blue mustache on its “face”? The mustache is a symbol of “Movember.” This is an international campaign to raise awareness of prostate cancer, as well as money to fund prostate cancer research.

Prostate Cancer

The prostate gland is an organ located in the male pelvis. The urethra passes through the prostate gland after it leaves the bladder and before it reaches the penis. The function of the prostate is to secrete zinc and other substances into semen during ejaculation. In the United States, prostate cancer is the most common type of cancer and the second leading cause of cancer death in people carrying prostate gland. About 80 percent of American individuals with the prostate will have cancerous cells in their prostate gland by the age of 80.

How Prostate Cancer Occurs

Prostate cancer occurs when glandular cells of the prostate mutate into tumor cells. Eventually, the tumor, if undetected, may invade nearby structures, such as the seminal vesicles. Tumor cells may also metastasize and travel in the bloodstream or lymphatic system to organs elsewhere in the body. Prostate cancer most commonly metastasizes to the bones, lymph nodes, rectum, or lower urinary tract organs.

Symptoms of Prostate Cancer

Early in the course of prostate cancer, there may be no symptoms. When symptoms do occur, they mainly involve urination, because the urethra passes through the prostate gland. The symptoms typically include frequent urination, difficulty starting and maintaining a steady stream of urine, blood in the urine, and painful urination. Prostate cancer may also cause problems with sexual function, such as difficulty achieving an erection or painful ejaculation.

Risk Factors for Prostate Cancer

Some factors that increase the risk of prostate cancer can be changed, and others cannot.

  • Risk factors that can be changed include a diet high in meat, a sedentary lifestyle, obesity, and high blood pressure.
  • Risk factors that cannot be changed include older age, a family history of prostate cancer, and African ancestry. Family history is an important risk factor, so genes are clearly involved. Many different genes have been implicated.

Diagnosing Prostate Cancer

The only definitive test to confirm a diagnosis of prostate cancer is a biopsy. In this procedure, a small piece of the prostate gland is surgically removed and then examined microscopically. A biopsy is done only after less invasive tests have found evidence that a patient may have prostate cancer.

A routine exam by a doctor may find a lump on the prostate, which might be followed by a blood test that detects an elevated level of prostate-specific antigen (PSA). PSA is a protein secreted by the prostate that normally circulates in the blood. Higher-than-normal levels of PSA can be caused by prostate cancer, but they may also have other causes. Ultrasound or magnetic resonance imaging (MRI) might also be undertaken to provide images of the prostate gland and additional information about cancer.

Treatment of Prostate Cancer

The average age at which men are diagnosed with prostate cancer is 70. Prostate cancer typically is such a slow-growing cancer that elderly patients may not require treatment. Instead, the patients are watched carefully over the subsequent years to make sure the cancer isn’t growing and posing an immediate threat — an approach that is called active surveillance. It is used for at least 50 percent of patients who are expected to die from other causes before their prostate cancer causes symptoms.

Treatment of younger patients — or those with more aggressively growing tumors — may include surgery to remove the prostate, chemotherapy, and/or radiation therapy (such as brachytherapy, see Figure (PageIndex{4})). All of these treatment options can have significant side effects, such as erectile dysfunction or urinary incontinence. Patients should learn the risks and benefits of the different treatments, and discuss them with their healthcare provider to decide on the best treatment options for their particular case.

Testicular Cancer

Reproductive cancer that is rare and most commonly affects young individuals is testicular cancer. The testes are the paired reproductive organs in the scrotum that produce sperm and secrete testosterone. The risk of testicular cancer is about four to five times greater in individuals of European than African ancestry. The cause of this difference is unknown.

Signs and Symptoms of Testicular Cancer

One of the first signs of testicular cancer is often a lump or swelling in one of the two testes. The lump may or may not be painful. If pain is present, it may occur as a sharp pain or a dull ache in the lower abdomen or scrotum. Some people with testicular cancer report a feeling of heaviness in the scrotum. Testicular cancer does not commonly spread beyond the testis, but if it does, it most often spreads to the lungs, where it may cause shortness of breath or a cough.

Diagnosis of Testicular Cancer

The main way that testicular cancer is diagnosed is by detection of a lump in the testis. This is likely followed by further diagnostic tests. An ultrasound may be done to determine the exact location, size, and characteristics of the lump. Blood tests may be done to identify and measure tumor-marker proteins in the blood that are specific to testicular cancer. CT scans may also be done to determine whether the disease has spread beyond the testis. However, unlike the case with prostate cancer, a biopsy is not recommended, because it increases the risk of cancer cells spreading into the scrotum.

Treatment of Testicular Cancer

Testicular cancer has one of the highest cure rates of all cancers. Three basic types of treatment for testicular cancer are surgery, radiation therapy, and/or chemotherapy. Generally, the initial treatment is surgery to remove the affected testis. If the cancer is caught at an early stage, the surgery is likely to cure the cancer and has nearly a 100 percent five-year survival rate. When just one testis is removed, the remaining testis (if healthy) is adequate to maintain fertility, hormone production, and other normal functions. Radiation therapy and/or chemotherapy may follow surgery to kill any tumor cells that might exist outside the affected testis, even when there is no indication that cancer has spread. In many cases, however, surgery is followed by surveillance instead of additional treatments.


1. What is erectile dysfunction? When does it occur?

2. Underlying causes of erectile dysfunction may include physiological and/or psychological factors. Identify some of these factors.

3. Discuss types of treatment for erectile dysfunction.

4. Define epididymitis. What is its most common cause?

5. Identify possible treatments for epididymitis. Why is treatment important, even when there are no symptoms?

6. Rank prostate cancer as a cause of cancer and cause of cancer death in men. What are some of the symptoms of prostate cancer?

7. List risk factors for prostate cancer.

8. How is prostate cancer detected?

9. In many cases, treatment for prostate cancer is unnecessary. Why? When is treatment necessary, and what are treatment options?

10. Testicular cancer is generally rare, but it is the most common cancer in one age group. What age group is it?

11. Identify possible signs and symptoms of testicular cancer.

12. How can testicular cancer be diagnosed?

13. Describe how testicular cancer is typically treated.

14. Which of the following is common in younger individuals (i.e. under age 39)?

A. prostate cancer

B. testicular cancer

C. epididymitis

D. B and C

15. A biopsy is important in cases of suspected _____________.

A. epididymitis

B. prostate cancer

D. B and C

Breast Disorders in Men

Breast enlargement in males is called either gynecomastia or pseudogynecomastia.

Gynecomastia is enlargement of the breast tissue itself, which consists of glands.

Pseudogynecomastia is the appearance of enlarged breast in overweight men. However, this enlargement is because of an increase in fat tissue around the breasts, not an enlargement of the gland tissue in the breast.

Gynecomastia sometimes occurs during infancy and puberty. The enlargement is usually normal and transient in puberty, lasting a few months to a few years. Breast enlargement also commonly takes place after age 50.

Did You Know.

Boys sometimes develop temporary breast enlargement during puberty.

In men, breast enlargement may be caused by

Certain disorders (including some liver disorders)

Certain drug therapies (including the use of female sex hormones and anabolic steroids and some drugs used to treat an enlarged prostate gland or prostate cancer)

Herbal products (such as lavender oils and tea tree oils in skin products)

Heavy use of marijuana, beer, alcohol, or heroin

Less commonly, male breast enlargement results from a hormonal imbalance, which can be caused by rare estrogen -producing tumors in the testes or adrenal glands.

One or both breasts may become enlarged. An enlarged breast may be tender. If tenderness is present, cancer is probably not the cause. Breast pain in men, as in women, is not usually a sign of cancer.

The doctor does a thorough interview and physical examination. Sometimes other tests such as blood tests or mammography are needed.

Generally, no specific treatment is needed. Breast enlargement often disappears on its own or after its cause is identified and treated. Surgical removal of excess breast tissue is effective but rarely necessary. Liposuction, a surgical technique that removes tissue through a suction tube inserted through a small incision, is the preferred surgical option and sometimes is followed by additional cosmetic surgery.

12.14 Reproductive and Developmental Toxicants

Reproductive toxicants are chemical, biohazardous, or physical agents that can impair the reproductive capabilities in men and/or women. Developmental toxicants interfere with proper growth or health of the child acting at any point from conception to puberty.

12.14.1 Adverse Effects Caused by Reproductive and Developmental Toxicants

  1. Genetic defects: Changes in germ cells that can be passed from one generation to the next, as well as genetic problems that arise at the point of fertilization (such as Down Syndrome). It is estimated that 20% of human malformations are due to inherited genetic defects that are present in the egg or sperm cell.
  2. Infertility: The inability of a couple to conceive after one year of regular intercourse without the use of contraceptives. One in twelve couples in the U.S. is infertile according to the Agency for Toxic Substances and Disease Registry (ATSDR). Hazardous exposures can cause infertility in males by interfering with hormones, damaging the testes (thus affecting sperm production), or by damaging the sperm leading to a reduction in sperm count, viability, motility, or functional capabilities. In women, the lack of ovulation or abnormal menstruation may cause infertility. This may be due to damage to the fallopian tubes, direct damage to the egg, or a change in the balance of sex hormones.
  3. Menstrual disorders: This effect has not been studied thoroughly however, any chemical that influences the balance of sex hormones could potentially cause menstrual irregularities.
  4. Impotence or decreased libido: Chemicals that affect the nervous system or the secretion of sex hormones have been shown to lower libido or alter sexual response in both males and females.
  5. Spontaneous abortion: Spontaneous abortion or miscarriage is the loss of the embryo or fetus before full term. Approximately 40% or more of all pregnancies end in spontaneous abortion (ATSDR). Spontaneous abortion may be caused when toxicants: a. Cause damage to the genetic material in the egg so that the embryo cannot survive b. Prevent the fertilized egg from implanting itself in the uterus or c. Directly affect the developing embryo or fetus, causing a lethal toxic effect.
  6. Stillbirth: Birth of a dead fetus. The death occurs late in the pregnancy or during birth.
  7. Birth defect: Physical abnormality or malformation present at birth, although it may not be detected. Two to three percent of all newborns have a serious birth defect (ATSDR). Approximately two-thirds of human birth defects have no known cause. The proportion that may be associated with exposure to hazardous substances is unknown. Teratogens are agents that cause birth defects to the embryo or fetus and usually occur during the first trimester.
  8. Low birth weight and premature birth: Agents can delay the growth or harm the health of the embryo or fetus without causing physical defects or death. Low birth weight is directly related to an increased risk of illness or death in the first year of life. Premature births are at risk for low birth weights and may suffer from the effects of immature organ systems.
  9. Childhood cancer: Carcinogens can affect the fetus by passing through the placenta to the fetus. These transplacetal carcinogens can later cause cancer in the child or young adult. Research in this area is limited however, work environments with exposures to metals, solvents, paints, and agricultural chemicals are of concern.
  10. Developmental disorders: Behavioral effects include hyperactivity, decreased attention span, slow learning ability, and in severe cases, mental retardation. These may be temporary or permanent effects. Due to limited studies, very few industrial chemicals that cause neurobehavioral defects have been identified.
  11. Breast milk and other exposures after birth: Some chemicals are stored in fat tissues and, since breast milk is rich in fat, infants can be exposed to these toxic chemicals. However, breastfeeding has many positive benefits that may outweigh the infant's risk of chemical exposure. Your healthcare provider should be consulted in these cases.
  12. Skin or clothing: Skin or clothing contaminated with chemicals can also be a route of exposure for infants and children at home. Using good work practices and leaving contaminated clothing at work will prevent this type of exposure.

12.14.2 Hazards of Reproductive and Developmental Toxicants

The greatest susceptibility to reproductive toxicants in women is usually during the first three to twelve weeks of pregnancy. During this period, a woman may not know that she is pregnant.

The nature and severity of the adverse effects depend on how much of the hazard the individual is exposed to, when and for how long, and how (by what route of exposure).

In order to appropriately recognize and control chemicals that may cause an increased risk of harm, three categories have been established. Toxicants that fall into Category 1 must be labeled Danger-Reproductive and Developmental Toxicant. The lab safety coordinator (ultimately the principal investigator or supervisor) is responsible for reviewing all lab chemicals and must determine whether any Category 1 chemicals are present. The lab safety coordinator also identifies any new Category 1 chemicals at the time of purchase. Pesticides have not been included in the tables.

Category 2 toxicants have sufficient animal evidence and limited human evidence and Category 3 have suspect or insufficient evidence.

12.14.3 Handling Procedures for Reproductive and Developmental Toxicants

Volatile reproductive toxicants must be handled inside a chemical fume hood to prevent inhalation exposure. Wear standard PPE (gloves, lab coat, and safety glasses) for handling reproductive toxicants. It is recommended that Section 12.11.8, Handling Procedure for Select Carcinogens, be followed when using Category 1 reproductive toxicants.

12.14.4 Storage of Reproductive and Developmental Toxicants

See Section 9, Proper Chemical Storage, for specific storage information. Reproductive toxicants should be labeled as such within the respective storage group.

12.14.5 Disposal of Reproductive and Developmental Toxicants

Refer to Chapter VI, Hazardous Waste Directory, for specific disposal information. Most reproductive toxicants will need to be labeled for collection by EH&S.

12.14.6 Emergency Response: Exposure

  1. Skin: Immediately remove affected clothing and flush contacted tissue with copious amounts of water for 15 minutes. If the skin is injured, proceed to the nearest hospital ER.
  2. Eye Contact: Rinse eyes with copious amounts of water for 15 minutes. Hold lids open while rinsing. Seek medical evaluation.

Complete an Accident-Illness Report Form as soon as possible and mail to EH&S at J3-200.

12.14.7 Emergency Response: Spills

Small spills can be cleaned with a universal absorbent while wearing safety goggles, gloves and a lab coat.

For large spills (>200 ml), evacuate the lab and call EH&S for clean-up.

12.14.8 Category 1 Reproductive and Developmental Toxicants: Sufficient Human Evidence

Category 1 agents are known human reproductive and/or developmental hazards. The scientific evidence to support this consists of sufficient epidemiologic evidence or human case studies along with strong supporting animal evidence for at least one adverse reproductive effect. Because the human data necessary to support this category are generally limited, there are currently few agents classified in this category. The potential reproductive effects listed are based on observation of toxic effects in studies of exposed humans or animals. Biohazardous and physical hazards are also included in this section.

Table Category 1

Reported Adverse Effects

Female infertility, spontaneous abortion, growth retardation, developmental disorders

Male and female infertility, spontaneous abortion, birth defects, and growth retardation

Cancer chemotherapeutic drugs (e.g., methotrexate, cyclophosphamide)

Male and female infertility, spontaneous abortion, birth defects, growth retardation, some contaminate breast milk

Reduced male sex drive, male and female infertility, spontaneous abortion, growth retardation, menstrual disorders, breast milk contamination

Female infertility, spontaneous abortion, growth retardation, functional deficit

Male and female infertility, birth defects, developmental disorders

Male infertility, genetic defects, altered sex ratios

Male infertility, functional deficit, childhood cancer

Spontaneous abortion, male infertility, growth retardation, developmental disorders

Male infertility, developmental disorders, birth defects, low birth weight or premature births

Male and female infertility, spontaneous abortion, growth retardation, functional deficit, breast milk contamination

Mercury (organic such as methyl mercury)

Male infertility, birth defects, growth retardation, functional deficit, breast milk contamination

Low birth weight, spontaneous abortion, developmental disorders, breast milk contamination

Altered sex ratio, spontaneous abortions, impotence

Polychlorinated biphenyls (PCBs)

Male and female infertility, spontaneous abortion, growth retardation, breast milk contamination

Birth defects, developmental disorders, spontaneous abortions

Low birth weight, developmental disorders, birth defects, menstrual disorders, male and female infertility

Reported Adverse Effects

Spontaneous abortion, birth defects, growth retardation, developmental disorders, breast milk contamination

Growth retardation, liver disease in infected offspring, breast milk contamination

Functional deficit, childhood cancer

Adverse pregnancy outcomes

Rubella virus (German measles)

Birth defects, growth retardation, developmental disorders

Spontaneous abortion, birth defects, developmental disorders

Varicella-zoster virus (chicken pox and shingles)

Birth defects, growth retardation

Reported Adverse Effects

Heavy physical exertion (e.g., repetitive heavy lifting, stooping and/or climbing)

Spontaneous abortion, growth retardation

Male and female infertility, spontaneous abortion, birth defects, growth retardation, developmental disorders, childhood cancer

12.14.9 Category 2 Reproductive and Developmental Toxicants: Sufficient Animal Evidence/Limited Human Evidence

The agents listed in this category are probable or possible human reproductive hazards. The scientific evidence to support this includes data from experimental animal studies and/or limited human data. The minimum evidence necessary is a single, well-conducted study in one experimental animal species for one adverse reproductive effect. The potential reproductive effects listed are based on observation of toxic effects in studies of exposed animals and humans.

Table Category 2

Acetaldehyde (with alcohol consumption)

Growth retardation, developmental disorders

Female infertility, birth defects, menstrual disorders

Male infertility, birth defects, reduced male sex drive

Anesthetic agents (e.g., nitrous oxide, halothane)

Male infertility, spontaneous abortion, birth defects, growth retardation, breast milk contamination

Spontaneous abortion, breast milk contamination

Antimony potassium tartrate

Premature birth, miscarriages, female infertility

Birth defects, spontaneous abortion

Female infertility, spontaneous abortion, birth defects, growth retardation, menstrual disorders

Reduced male sex drive, male infertility, female infertility

Male infertility, decreased libido, impotence, breast milk contamination

Male and female infertility, birth defects, growth retardation

Male and female infertility, birth defects, growth retardation, developmental disorders, breast milk contamination

Male and female infertility, genetic defects

Male and female infertility

Reported Adverse Effects (continued)

Spontaneous abortion, birth defects

Spontaneous abortion, birth defects

Birth defects, spontaneous abortion, male infertility

Dimethylformamide, N, N (DMF)

Spontaneous abortion, stillbirths, birth defects, female infertility

Male and female infertility, spontaneous abortion, birth defects, breast milk contamination

Male infertility, birth defects

Ethylene glycol monoethyl ether (EGEE)

Birth defects, female and male infertility, menstrual disorders

Ethylene glycol monomethyl ether (EGME)

Male infertility, birth defects, developmental disorders

Male and female infertility, spontaneous abortion, birth defects, growth retardation

Female infertility, spontaneous abortion

Female infertility, birth defects, menstrual disorders

Glycidyl ethers (e.g., allyl glycidyl ether, phenyl glycidyl ether)

Birth defects and male infertility among patients taking lithium

Reduced male sex drive, male infertility, breast milk contamination

Mercury (inorganic salts and metallic Hg)

Reduced male sex drive, male and female infertility, spontaneous abortion, birth defects, growth retardation, breast milk contamination

Male and female infertility, spontaneous abortion, developmental defects

Reported Adverse Effects (continued)

Reduced male sex drive, female infertility, birth defects

Spontaneous abortion, developmental disorders

Polyvinyl chloride (PVC resin)

Female infertility, spontaneous abortion, stillbirths

Spontaneous abortion, birth defects, female infertility, menstrual disorders, breast milk contamination

Birth defects, developmental disorders, spontaneous abortion, impotence, female infertility, menstrual disorders, breast milk contamination

Spontaneous abortions, female infertility, low fetal weights, birth defects

Male and female infertility, spontaneous abortion, breast milk contamination

Spontaneous abortion, birth defects, male infertility, menstrual disorders, breast milk contamination

Female infertility, spontaneous abortion, developmental disorders, birth defects, menstrual disorders, breast milk contamination

Male and female infertility, spontaneous abortion, birth defects

Reduced male sex drive, spontaneous abortion, birth defects, childhood cancer

Female infertility, birth defects, menstrual disorders, breast milk contamination

Reported Adverse Effects

Low atmospheric pressure (hypobaric)

Male infertility, growth retardation

High atmospheric pressure (hyperbaric)

Male infertility, birth defects

12.14.10 Category 3 Reproductive and Developmental Toxicants: Suspect/Insufficient Evidence

The agents in this category are possible or uncertain reproductive hazards. They are suspected to affect reproductive health but the data are insufficient. The existing data are from animal studies with no human data available.

Male Reproductive Function

Male reproductive function involves sexual arousal, erection, orgasm, and ejaculation of semen.

The penis becomes erect through a complex interaction of physiologic and psychologic factors.

Contractions during ejaculation force semen into the urethra and then out of the penis.

During sexual arousal, the penis becomes erect, enabling penetration during sexual intercourse. An erection results from a complex interaction of neurologic, vascular, hormonal, and psychologic stimuli. Pleasurable stimuli cause the brain to send nerve signals through the spinal cord to the penis. The arteries supplying blood to the erectile tissue (the corpora cavernosa and corpus spongiosum—see figure Male Reproductive Organs) respond by widening (dilating). The widened arteries dramatically increase blood flow to these erectile areas. At the same time, muscles around the veins that normally drain blood from the penis tighten, slowing the outflow of blood and elevating blood pressure in the penis. This combination of increased inflow and decreased outflow is what causes the penis to become engorged with blood and increase in length, diameter, and stiffness.

Orgasm is the climax of sexual excitement. At orgasm, ejaculation usually occurs, caused when stimulation of the glans penis and other stimuli send signals to the brain and spinal cord. Nerves stimulate muscle contractions along the seminal vesicles, prostate, and the ducts of the epididymis and vas deferens. These contractions force semen into the urethra. Contraction of the muscles around the urethra further propels the semen through and out of the penis. The neck (base) of the bladder also constricts to keep semen from flowing backward into the bladder.

Once ejaculation takes place—or the stimulation stops—the arteries constrict and the veins open, reducing blood inflow, increasing blood outflow, and causing the penis to become limp (detumescence). After detumescence, erection cannot be obtained for a period of time (refractory period), commonly about 20 minutes in young men.

Breast cancer in men

Men can develop breast cancer, although 99% of all breast cancers develop in women. In the United States, about 2,360 men develop breast cancer each year, and about 430 die. Because male breast cancer is uncommon, it may not be suspected as a cause of symptoms. As a result, male breast cancer often progresses to an advanced stage before it is diagnosed. The prognosis is the same as that for a woman whose cancer is at the same stage.

As in women, breast cancer in men causes breast lumps that should be evaluated. Diagnostic techniques are the same as those used in women.

As in women, treatment options for breast cancer in men include surgery, radiation therapy, and chemotherapy. However, in men, conserving the breast after surgery is not a concern.

Estrogen makes some breast cancers grow. Estrogen is the main female sex hormone, but it is present in males in low amounts. If an examination of tissue samples shows that estrogen is making the cancer grow, estrogen is suppressed with drugs such as tamoxifen .

Testosterone-Replacement Therapy

Many men with normal testosterone levels are interested in taking testosterone to slow or reverse development of characteristics of low testosterone . However, currently testosterone replacement therapy (TRT) is recommended only for men with both symptoms of low testosterone and abnormally low blood levels of testosterone , a condition called hypogonadism. Recent studies have found conflicting evidence suggesting a possible increased risk of heart attack and stroke in men who take TRT.

Side effects of testosterone -replacement therapy

Testosterone treatment may rarely have certain side effects, such as snoring, increase in symptoms of urinary tract blockage (usually caused by benign prostatic hyperplasia), mood changes, acne, blood clots, and breast enlargement. Testosterone sometimes causes the body to make too many red blood cells, possibly increasing the risk for various disorders, such as blood clots and strokes.

Currently, testosterone treatment is thought to have no effect on the development or progression of prostate cancer. However, this subject is not entirely understood, and men should talk with their doctors about their risk of developing prostate cancer.

Follow-up to testosterone -replacement therapy

Men taking testosterone need to be checked every few months for changes in their blood count and for prostate cancer. Such testing may detect cancers early, when they are more likely to be curable. Some men with prostate cancer may take testosterone treatment, but they should be checked even more frequently by their doctor.

How does the male reproductive system work?

The main activities of the male reproductive system include:

Puberty: Getting your body ready to produce sperm and have sex

Erection: Getting the penis stiff so that you can have sex

Ejaculation: Releasing semen

What are sperm and semen?

Sperm are the male sex cells, which can fertilize a female's egg and start a pregnancy

Semen is the liquid that contains sperm and comes out of your penis when you ejaculate

Your testicles make millions of sperm, which go into the epididymis to mature. Then they travel through a long tube called the vas deferens on their way to the urethra and out the penis.

Semen is made up of sperm and a lot of liquid that nourishes and transports the sperm. The liquid is produced by your seminal vesicles and prostate and mixes with sperm during ejaculation.

What is an erection?

An erection is when your penis gets bigger and stiff (erect). Erections happen when you're sexually aroused and is made possible by both physical and mental factors.

During an erection, the spaces inside your penis fill with blood, making the penis longer, wider, and more firm. Your penis fills with blood because the arteries that bring blood into the penis widen so more blood flows in, and the veins constrict so less blood flows out.

What is ejaculation?

Ejaculation is the release of semen from your penis. Sexual stimulation causes an orgasm (the peak of sexual excitement). During an orgasm, muscles squeeze and push semen into your urethra and out your penis.

What happens after ejaculation?

After ejaculation happens or if sexual stimulation stops, more blood flows out of your penis and less flows in, causing your penis to get limp. Another erection can’t happen for a period of time, usually about 20 minutes in young men.

Reproductive tract biology: Of mice and men

The study of male and female reproductive tract development requires expertise in two separate disciplines, developmental biology and endocrinology. For ease of experimentation and economy, the mouse has been used extensively as a model for human development and pathogenesis, and for the most part similarities in developmental processes and hormone action provide ample justification for the relevance of mouse models for human reproductive tract development. Indeed, there are many examples describing the phenotype of human genetic disorders that have a reasonably comparable phenotype in mice, attesting to the congruence between mouse and human development. However, anatomic, developmental and endocrinologic differences exist between mice and humans that (1) must be appreciated and (2) considered with caution when extrapolating information between all animal models and humans. It is critical that the investigator be aware of both the similarities and differences in organogenesis and hormone action within male and female reproductive tracts so as to focus on those features of mouse models with clear relevance to human development/pathology. This review, written by a team with extensive expertise in the anatomy, developmental biology and endocrinology of both mouse and human urogenital tracts, focusses upon the significant human/mouse differences, and when appropriate voices a cautionary note regarding extrapolation of mouse models for understanding development of human male and female reproductive tracts.

Keywords: Adenosis Alpha-fetoprotein Benign prostatic hyperplasia Clitoris Hypospadias Mullerian duct Penis Prepuce Prostate Uterus Vagina.

Copyright © 2019 International Society of Differentiation. Published by Elsevier B.V. All rights reserved.


The mouse penile glans (A) lies within an extensive preputial space defined by…

1mm beyond the urethral meatus in mice (A).

Adult human and mouse penile…

Adult human and mouse penile anatomy. (A) Drawing of human penis in mid-sagittal…

Adult human and mouse penile anatomy. (A) Drawing of human penis in mid-sagittal view and (B) in transverse section. Note junction of the pendulous external portion and the internal portion of the human penis indicated by the dotted line in (A). (C) Photograph of a dissected adult mouse penis. The junction between the internal and external portions of the mouse penis occurs at the right-angle bend denoted by the dotted line and associated labels, “internal” and “external”. The forceps hold one of the bilateral crura. The internal portion contains the body of the mouse penis, while the external portion is called the glans. The glans in (C) cannot be seen because it lies within the preputial space (dotted lines) the position of the glans is indicated by. (D) Mid- sagittal hematoxylin–eosin stained section of the adult mouse penis with the external prepuce removed. (E) The mouse glans penis within the proximal portion of the external prepuce. Note reflection of epithelium of the external prepuce onto the surface of the penis indicated by the large solid arrows in both (D & E). (Adapted from Rodriguez et al. 2011 and Cunha et al. 2015 with permission).

Diagrams of divergent development of…

Diagrams of divergent development of mouse (A) and human (B) urethral development. (A)…

Human fetal prostates at 15…

Human fetal prostates at 15 (A) and 19 weeks (B) stained for smooth…

Diagram of the reproductive tract…

Diagram of the reproductive tract of a neonatal mouse. The fused Müllerian ducts…

Diagrams of adult human and…

Diagrams of adult human and mouse female reproductive tracts. In humans most of…

Sagittal sections of a 21-week…

Sagittal sections of a 21-week female reproductive tract. (A) depicts the upper portion…

Light sheet microscopy of a…

Light sheet microscopy of a human female reproductive tract at 9.5 weeks stained…

Breast cancer in men

Men can develop breast cancer, although 99% of all breast cancers develop in women. In the United States, about 2,360 men develop breast cancer each year, and about 430 die. Because male breast cancer is uncommon, it may not be suspected as a cause of symptoms. As a result, male breast cancer often progresses to an advanced stage before it is diagnosed. The prognosis is the same as that for a woman whose cancer is at the same stage.

As in women, breast cancer in men causes breast lumps that should be evaluated. Diagnostic techniques are the same as those used in women.

As in women, treatment options for breast cancer in men include surgery, radiation therapy, and chemotherapy. However, in men, conserving the breast after surgery is not a concern.

Estrogen makes some breast cancers grow. Estrogen is the main female sex hormone, but it is present in males in low amounts. If an examination of tissue samples shows that estrogen is making the cancer grow, estrogen is suppressed with drugs such as tamoxifen .


Intersexuality (having both male and female characteristics) may be noticeable at birth or may become apparent after puberty. Intersexuality noticeable at birth may be classified as female or male pseudohermaphroditism or true hermaphroditism. Female pseudohermaphroditism, or female intersex, may be of adrenal or nonadrenal type. The adrenal type develops because of an inborn error in the metabolism of the adrenal hormone cortisol that leads to an increased secretion of corticotropin (ACTH) and consequent excessive secretion of androgens (male sex hormones). A newborn female with this condition is a chromosomal female and resembles a normal female, but an excess of male hormone has a masculinizing effect on the external genitalia the vagina tends to be connected to the urethra and the clitoris is enlarged, as are the labia (the labia majora are prominent folds of skin, corresponding to the scrotum in the male). Effective treatment can be achieved by administration of adrenal hormones (e.g., cortisone, hydrocortisone), which suppress the pituitary so that its stimulus to adrenal production of androgenic hormones is minimized. The nonadrenal type of intersex is seen in infants whose mothers have been administered synthetic androgens or progestational compounds (substances that stimulate changes in the uterus that further the implantation and growth of the fertilized ovum) during pregnancy. Rarely, the condition is associated with the presence in the mother of a tumour of the ovary or adrenal gland. The newborn infant is a female with varying degrees of ambiguous genitalia no treatment is necessary, and normal female development occurs at puberty.

Male pseudohermaphrodites are males with varying deficiencies of internal and external virilization. Most commonly, the male intersex has a markedly hypospadiac penis, undescended testes, a cleft scrotum, and an enlarged prostatic utricle a complete uterus and fallopian tubes may be found, with the vagina opening into the posterior wall of the urethra. (Such persons are pseudohermaphrodites in that they do not have ovaries.)

True hermaphrodites have recognizable ovarian and testicular tissue. A uterus is always present, but the internal genitalia otherwise vary greatly, often including both male and female structures. The external genitalia are usually ambiguous, and a sizable phallus is present therefore, most of these children are raised as males. At puberty, over 80 percent of them develop enlarged breasts, and approximately half menstruate. Most hermaphrodites are chromatin positive—that is, they have, within and near the periphery of the nuclei of their cells, a substance, chromatin, that is normally found in the cells of females but not in those of males—and over half have a characteristically female set of chromosomes in their peripheral blood cells.

Surgical and hormonal therapy directed at producing either a male or a female configuration of the body is based on the existing physical and psychological findings. Treatment also depends upon the age at which the diagnosis is made.

Klinefelter syndrome, Turner syndrome, and testicular feminization are intersexuality syndromes that become apparent prior to or after puberty. Klinefelter syndrome is a genetic disorder of males who have an extra sex chromosome (XXY) and subsequently are usually infertile, have small testes, and have enlarged breasts at the time of puberty (gynecomastia). Males with this syndrome have an increased risk of various autoimmune disorders such as diabetes mellitus and lupus.

Turner syndrome is a condition of females who, in the classic form, carry only a single X chromosome (XO). Characteristically, such persons are short, do not menstruate, and have a deficiency of estrogen (a female sex hormone) there is a distinctive cluster of congenital anomalies attached to this syndrome.

Testicular feminization, or androgen insensitivity syndrome, is caused by genetic mutations on the X chromosome that cause a male to be resistant to the action of androgens (male hormones). Affected persons seem to be normally developed females but have a chromosomal sex that is that of the normal male. The gonads are well-developed testes, and evidence indicates that there is a normal production of testosterone (male hormone), but there is cellular resistance to the action of this hormone, and therefore the affected person becomes female in appearance. Because these gonads are apt to form malignant tumours, they are usually removed surgically. Female sexual characteristics are then maintained by the administration of estrogenic hormones.