Reproductive System Flashcards
- The female sex hormones—estrogen and progesterone—have numerous functions. One function of these hormones affects the endometrium, causing the uterus to undergo a cyclical series of events known as the uterine cycle (Fig. 17.11). Twenty-eight-day cycles are divided as follows:
*
Uterine Cycle: Nonpregnant
Contraceptives** are medications and devices that reduce the chance of pregnancy. Oral contraception, known as **birth control pills, is the most effective form of contraception. These pills contain a combination of estrogen and progesterone. Most birth control pills are taken daily. For the first 21 days, the pills contain active hormones. This is followed by 7 days of inactive pills. The estrogen and progesterone in the birth control pill or a patch applied to the skin effectively shuts down the pituitary production of both FSH and LH. Follicle development in the ovary is prevented. Because ovulation does not occur, pregnancy cannot take place. Women taking birth control pills or using a patch should see a physician regularly because of possible side effects.
A great deal of research is being devoted to developing safe and effective hormonal birth control for men. Implants, pills, patches, and injections are being explored as ways to deliver testosterone and/or progesterone at adequate levels to suppress sperm production. Even the most successful formulations are still in the experimental stage and are unlikely to be available outside of clinical trials for at least a few more years.
An intrauterine device (IUD) is a small piece of molded plastic, and sometimes copper, that is inserted into the uterus by a physician (Fig. 17.14a). IUDs alter the environment of the uterus and uterine tubes to reduce the possibility of fertilization. If fertilization should occur, implantation cannot take place.
Males produce sperm within testes, and females produce eggs within ovaries.
- Males nurture and transport the sperm in ducts until they exit the penis. Females transport the eggs in uterine tubes to the uterus.
- The male penis functions to deliver sperm to the female vagina, which receives the sperm. The vagina also transports menstrual fluid to the exterior and acts as the birth canal.
- The uterus of the female allows the fertilized egg to develop within her body. After birth, the female breast provides nourishment in the form of milk.
Mitosis and Meiosis
Before examining the two different forms of cell division that occur during the human life cycle, it is important to recognize that our genetic instructions, or DNA, are distributed among 46 chromosomes within the nucleus. These 46 chromosomes exist in 23 pairs, with each pair containing a contribution from both the male and female parent. Most of the cell types in the body have 46 chromosomes. During the majority of our life cycle, our cells divide by a process called mitosis (see Section 19.3). Mitosis is duplication division, meaning that each of the cells that exit mitosis has the same complement of 46 chromosomes. In other words, when a cell divides, it produces exact copies of itself by mitosis, much as a copier machine does with a page of notes. In the life cycle of a human, mitosis is the type of cell division that plays an important role during growth and repair of tissues (Fig. 17.1).
Figure 17.1 The human life cycle. The human life cycle has two types of cell division: mitosis, in which the chromosome number stays constant, and meiosis, in which the chromosome number is reduced. During growth or cell repair, mitosis ensures that each new cell has 46 chromosomes. During production of sex cells, the chromosome number is reduced from 46 to 23. Therefore, an egg and a sperm each have 23 chromosomes, so that when the sperm fertilizes the egg, the new cell, called a zygote, has 46 chromosomes.
For the purposes of reproduction, special cells in the body undergo a type of cell division called meiosis. Meiosis takes place only in the testes of males during the production of sperm and in the ovaries of females during the production of eggs. Meiosis has two functions (see Section 19.4), the first of which is called reduction division. During meiosis, the chromosome number is reduced from the normal 46 chromosomes, called the diploid or 2n number, down to 23 chromosomes, called the haploid or n number of chromosomes. This process requires two successive divisions, called meiosis I and meiosis II, and is involved in the formation of gametes, or sex cells. As explained in Section 19.4, meiosis also introduces genetic variation, thus ensuring that the new individual is not an exact copy of either parent.
Mitosis • Mitosis: – Is a type of duplication division in which a cell makes an exact copy of itself –This process is used for growth and repair of tissues – Used by body cells (cells other than sex cells)
Puberty • Sequence of events where a child becomes a sexually competent young adult • Girls: 10-14 • Boys: 12-16 • At completion, individual is capable of producing offspring
DNA in body and sex cells • Body cells –Each body cell has 46 chromosomes (23 pairs) within the nucleus. –Cells that have pairs of chromosomes are called diploid (2n)
17.2 Male Reproductive SystemLEARNING OUTCOMES
Upon completion of this section, you should be able to
Identify the structures of the male reproductive system and provide a function for each.
Describe the location and stages of spermatogenesis.
Summarize how hormones regulate the male reproductive system.
The male reproductive system includes the organs listed in Table 17.1 and shown in Figure 17.2.
OrganFunctionTestesProduce sperm and sex hormonesEpididymidesDucts where sperm mature and some sperm are storedVasa deferentiaConduct and store spermSeminal vesiclesContribute nutrients and fluid to semenProstate glandContributes fluid to semenUrethraConducts spermBulbourethral glandsContribute mucus-containing fluid to semenPenisOrgan of sexual intercourseTable 17.1Male Reproductive OrgansTable Summary:
Figure 17.2 The male reproductive system. The testes produce sperm. The seminal vesicles, the prostate gland, and the bulbourethral glands provide a fluid medium for the sperm, which move from the vas deferens through the ejaculatory duct to the urethra in the penis. The foreskin (prepuce) is removed when a penis is circumcised.
The male gonads, or primary sex organs, are paired testes (sing., testis), suspended within sacs called the scrotum.Sperm produced by the testes mature within theepididymis(pl., epididymides), a tightly coiled duct lying just outside each testis. Maturation seems to be required for sperm to swim to the egg. When sperm leave an epididymis, they enter avas deferens(pl., vasa deferentia), also called the ductus deferens. The sperm may be stored for a time in the vas deferens. Each vas deferens passes into the abdominal cavity, where it curves around the bladder and empties into an ejaculatory duct. The ejaculatory ducts enter theurethra.
At the time of ejaculation, sperm leave the penis in a fluid called semen.The seminal vesicles, the prostate gland, and the bulbourethral glands add secretions to the semen. A pair ofseminal vesicles**lie at the base of the bladder, and each has a duct that joins with a vas deferens.**Bulbourethral glands**(also called Cowper’s glands) are pea-sized organs that lie posterior to the prostate on either side of the urethra. Their secretion makes the semen gelatinous. The_prostate gland_is a single, doughnut-shaped gland that surrounds the upper portion of the urethra just below the bladder. In older men, the prostate can enlarge and squeeze off the urethra, making urination painful and difficult. This condition is discussed in more detail in the Health feature “Urinary Difficulties Due to an Enlarged Prostate” inSection 11.5**.
Each component of semen has a particular function. Sperm are more viable in a basic solution; semen, milky in appearance, has a slightly basic pH (about 7.5). Swimming sperm require energy; semen contains the sugar fructose, which serves as an energy source. Semen also contains prostaglandins, chemicals that cause the uterus to contract. These contractions help propel the sperm toward the egg.
The Penis and Male Orgasm
The penis (Fig. 17.3) is the male organ of sexual intercourse. It also contains the urethra of the urinary system. The penis has a long shaft and an enlarged tip called the glans penis. The layer of skin covering the glans penis, called the foreskin, may be removed surgically by circumcision shortly after birth (see the Health feature “Manipulation of the Genitalia” in Section 17.3).Page 358
Figure 17.3 The structure of the penis. a. The shaft of the penis ends in an enlarged tip called the glans penis. In uncircumcised males, this is partially covered by a foreskin (prepuce). b. Micrograph of shaft in cross-section showing location of erectile tissue.
(b) ©Anatomical Travelogue/Science Source
Spongy, erectile tissue containing distensible blood spaces extends through the shaft of the penis. During sexual arousal, autonomic nerves release nitric oxide (NO). This stimulus leads to the production of cGMP (cyclic guanosine monophosphate), a high-energy compound similar to ATP. The cGMP causes the smooth muscle of incoming arterial walls to relax and the erectile tissue to fill with blood. The veins that take blood away from the penis are compressed, and the penis becomes erect. Erectile dysfunction (ED) (formerly called impotency) is the inability to achieve or maintain an erection suitable for sexual intercourse. ED may be caused by a number of factors, including poor blood flow, certain medications, and many illnesses. Medications for the treatment of erectile dysfunction inhibit the enzyme that breaks down cGMP, ensuring that a full erection Page 359will take place. Some of these medications can cause vision problems, because the same enzyme occurs in the retina. During an erection, a sphincter closes off the bladder, so that no urine enters the urethra.
As sexual stimulation intensifies, sperm enter the urethra from each vas deferens, and the glands contribute secretions to the seminal fluid. Once semen is in the urethra, rhythmic muscle contractions cause it to be expelled from the penis in spurts (ejaculation).
The contractions that expel semen from the penis are a part of male orgasm, the physiological and psychological sensations that occur at the climax of sexual stimulation. The psychological sensation of pleasure is centered in the brain. However, the physiological reactions involve the reproductive organs and associated muscles, as well as the entire body. Marked muscular tension is followed by contraction and relaxation. Following ejaculation and/or loss of sexual arousal, the penis returns to its normal flaccid state. Usually, a period of time, called the refractory period, follows during which stimulation does not bring about an erection. The length of the refractory period increases with age.
There may be in excess of 100 million sperm in the 3.5 ml of semen expelled during ejaculation. The sperm count can be much lower than this, however, and fertilization of the egg by a sperm can still take place.
Male Gonads: The Testes
The testes, which produce sperm as well as the male sex hormones, lie outside the abdominal cavity of the male, within the scrotum. The testes begin their development inside the abdominal cavity. They descend into the scrotal sacs through the inguinal canal during the last 2 months of fetal development. If the testes do not descend and the male is not treated or operated on to place the testes in the scrotum, sterility (the inability to produce offspring) usually follows. This is because the internal temperature of the body is too high to produce viable sperm. The scrotum helps regulate the temperature of the testes by holding them closer to or farther away from the body.
SCIENCE IN YOUR LIFEBoxers or briefs?
The scrotum’s role in male physiology is to keep the temperature of the testes lower than body temperature. The lower temperature is necessary for normal sperm production. It might follow that the man’s type of underwear can change that temperature, affecting sperm production. However, research has not supported this assumption. The style of underwear worn by a man, loose or close fitting, has not been shown to affect sperm count or fertility significantly.
Seminiferous Tubules
A longitudinal section of a testis shows that it is composed of compartments, called lobules, each of which contains one to three tightly coiled seminiferous tubules (Fig. 17.4a). A microscopic cross-section of a seminiferous tubule reveals that it is packed with cells undergoingspermatogenesis(Fig. 17.4b), the production of sperm.
Meiosis • Meiosis is a reductional division of cells that occurs only in the gametes, where the resulting cells contain 23 chromosomes (body cells =46) • Egg + sperm = zygote - get a complete set of 46 chromosomes • These cells then divide like mitosis and a new baby is created • Therefore each body cell is diploid and has 46 chromosomes (23 pairs) within the nucleus and have 2 sets of chromosomes ( a pair of each chromosome) 17.1 Human life cycle 8 The human life cycle Figure 17.1 The human life cycle. 17.1 Human Life Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2n zygote 2n = 46 diploid (2n) haploid (n) n = 23 MEIOSIS n n 2n 2n MITOSIS MITOSIS 2n egg sperm FERTILIZATION 9 17.1 Human Life Cycle Meiosis and mitosis animation You must be connected to the internet to view this animation and click on the link!
DNA in body and sex cells • Body cells –Each body cell has 46 chromosomes (23 pairs) within the nucleus. –Cells that have pairs of chromosomes are called diploid (2n)
Figure 17.11 Female hormone levels during the ovarian and uterine cycles. During the follicular phase, FSH released by the anterior pituitary promotes the maturation of a follicle in the ovary. The ovarian follicle produces increasing levels of estrogen, which causes the endometrium to thicken during the proliferative phase of the uterine cycle. After ovulation and during the luteal phase of the ovarian cycle, LH promotes the development of the corpus luteum. Progesterone, in particular, causes the endometrial lining to become secretory. Menses, due to the breakdown of the endometrium, begins when progesterone production declines to a low level.
Puberty • Sequence of events where a child becomes a sexually competent young adult • Girls: 10-14 • Boys: 12-16 • At completion, individual is capable of producing offspring
Figure 17.12 The effect of pregnancy on the corpus luteum and endometrium. If pregnancy occurs, the corpus luteum does not regress. Instead, the corpus luteum is maintained and secretes increasing amounts of progesterone. Therefore, menstruation does not occur, and the uterine lining, where the embryo resides, is maintained.
- Eventually, the placenta produces progesterone and some estrogen. The corpus luteum is no longer needed and thus regresses.
- Many women use birth control pills to prevent pregnancy (see Section 17.5). The most commonly used pills include active pills, containing a synthetic estrogen and progesterone, taken for 21 days, followed by 7 days of taking inactive pills that do not contain these hormones (Fig. 17.13).
- The uterine lining builds up to some degree while the active pills are being taken.
- Progesterone decreases after the last of the active pills are taken, causing menstruation. Some women skip taking the inactive pills and start taking a new pack of active pills right away to skip menstruation (a period).
- Birth control pills are available that consist of 3 months of active pills. Women taking them have only four menstrual periods a year.
Several means are available to reduce or enhance our reproductive potential. Birth control methods are used to regulate the number of children an individual or a couple has. For individuals who are experiencing infertility, or an inability to achieve pregnancy, a number of assisted reproductive technologies may be used to increase the chances of conceiving a child.
See Figure 17.1
Comparison of Mitosis and Meiosis
Page 357Following meiosis, the haploid cells develop into either sperm (males) or eggs (females). The flagellated sperm is small compared to the egg. It is specialized to carry only chromosomes as it swims to the egg. The egg is specialized to await the arrival of a sperm and to provide the new individual with cytoplasm in addition to chromosomes. The fusing of the egg and sperm form a cell called the zygote. Because a sperm has 23 chromosomes and the egg has 23 chromosomes, the zygote has 46 chromosomes altogether. Without meiosis, the chromosome number in each generation would double, and the cells would no longer be able to function.
Male anatomy
1.Scrotum (1) 2.Testes (2) (each called testis) 1.Epididymides (2) (each called epididymus) 2.Vasa deferentia (2) (each called vas deferens/ductus deferens) 3.Urethra (1) 4. Accessory glands (3 total): Seminal vesicles, prostate gland, bulbourethral glands 5.Penis (1)
- pelvic cavity usually has a larger relative size compared with that of males.The is wider and deeper in females, so the
- The female pelvis tilts forward,
- so females tend to have more of a lower back curve than males, an abdominal bulge, and protruding buttocks.
- This means that females have wider hips than males and
- their thighs converge at a greater angle toward the knees.
- *
pelvic girdle
Some of the Procedures Used
If a man has low sperm count or motility, artificial or intrauterine insemination of his partner with a large number of specially selected sperm may be done to stimulate pregnancy. Although there are dangers in all medical procedures, artificial insemination is generally safe.
If a woman is infertile because of physical abnormalities in her reproductive system, she may be treated surgically. Whereas surgeries are now very sophisticated, they nonetheless have risks, including bleeding, infection, organ damage, and adverse reactions to anesthesia. Similar risks are associated with collecting eggs for in vitro fertilization (IVF). To ensure the collection of several eggs, a woman may be placed on hormone-based medications that stimulate egg production. Such medications may cause ovarian hyperstimulation syndrome—enlarged ovaries and abdominal fluid accumulation. In mild cases, the only symptom is discomfort, but in severe cases (though rare), a woman’s life may be endangered. In any case, the fluid has to be drained.
Usually, IVF involves the creation of many embryos; the healthiest-looking ones are transferred into the woman’s body. Others may be frozen for future attempts at establishing pregnancy, given to other infertile couples, donated for research, or destroyed. Of those that are transferred, none, one, or all might develop into fetuses. The significant increase in multifetal pregnancies in the United States in the last 15 years has been largely attributed to fertility treatment (Fig. 17B). Though the number of triplet and higher-number multiple pregnancies started to level off in 1999, twin pregnancies continue to climb.
Figure 17B Reproductive technologies may lead to multiple births.
©Nancy R. Cohen/Getty Images
They may seem like a dream come true, but multifetal pregnancies are difficult. The mother is more likely to develop complications, such as gestational diabetes and high blood pressure, than are women carrying single babies. Positioning of the babies in the uterus may make vaginal delivery less likely, and there is likely a chance of preterm labor. Babies born prematurely face numerous hardships. Infant death and long-term disabilities are also more common with multiple births. This is true even of twins. Even if all babies are healthy, parenting “multiples” poses unique challenges.
What Happens to Frozen Embryos?
Despite potential trials, thousands of people undergo fertility treatment every year. Its popularity has brought a number of ethical issues to light. For example, the estimated high numbers of stored frozen embryos (a few hundred thousand in the United States) has generated debate about their fate, complicated by the fact that the long-term viability of frozen embryos is not well understood. Scientists may worry that embryos donated to other couples are ones screened out from one implantation and not likely to survive. Some religious groups strongly oppose destruction of these embryos or their use in research. Patients for whom the embryos were created generally feel that they should have sole rights to make decisions about their fate. However, a fertility clinic may no longer be receiving monetary compensation for the storage of frozen embryos and may be unable to contact the couples for whom they were produced. The question then becomes whether the clinic now has the right to determine their fate.
Who Should Be Treated?
Additionally, because fertility treatment is voluntary, is it ever acceptable to turn some people away? What if the prospect of a satisfactory outcome is very slim or almost nonexistent? This may happen when one of the partners is ill or the woman is at an advanced age. Should a physician go ahead with treatment even if it might endanger a woman’s (or baby’s) health? Those in favor of limiting treatment argue that a physician has a responsibility to prevent potential harm to a patient. On the other hand, there is concern that if certain people are denied fertility for medical reasons, might they be denied for other reasons also, such as race, religion, sexuality, or income?
Questions to Consider
Should couples go to all lengths to have children even if it could endanger the life of one or both spouses?
Should couples with “multiples” due to infertility treatment receive assistance from private and public services?
To what lengths should society go to protect frozen embryos?
Do you think that anyone should be denied fertility treatment? If so, what factors do you think a doctor should take into consideration when deciding whether to provide someone with fertility treatment?
Many couples who cannot reproduce in the usual manner adopt a child. Others sometimes try one of the assisted reproductive technologies discussed in the following paragraphs.
Assisted Reproductive Technologies
Assisted reproductive technologies consist of techniques used to increase the chances of pregnancy. Often, sperm and/or eggs are retrieved from the testes and ovaries, and fertilization takes place in a clinical or laboratory setting.
SCIENCE IN YOUR LIFEHow many babies are born annually in the United States using ART?
The very first IVF baby born in the United States was Elizabeth Carr on December 28, 1981. Since that time, assisted reproductive technologies (ART) have improved along with their success rates. In 2014, more than 70,000 babies were born in the United States as a result of ART. This represents almost 1% of the total conceptions in the United States.
Artificial Insemination by Donor (AID)
During artificial insemination, sperm are placed in the vagina by a physician. Sometimes a woman is artificially inseminated by her partner’s sperm. This is especially helpful if the partner has a low sperm count, because the sperm can be collected over time and concentrated, so that the sperm count is sufficient to result in fertilization. Often, however, a woman is inseminated by sperm acquired from a donor who is a complete stranger to her. At times, a combination of partner and donor sperm is used.
Page 374A variation of AID is intrauterine insemination (IUI). In IUI, fertility drugs are given to stimulate the ovaries. Then, the donor’s sperm are placed in the uterus, rather than in the vagina.
If the prospective parents wish, sperm can be sorted into those believed to be X-bearing or Y-bearing to increase the chances of having a child of the desired sex. Fertilization of an egg with an X-bearing sperm results in a female child. Fertilization by a Y-bearing sperm yields a male child.
In Vitro Fertilization (IVF)
During in vitro fertilization (IVF), conception occurs in laboratory glassware. Ultrasound machines can now spot follicles in the ovaries that hold immature eggs; therefore, the latest method is to forgo the administration of fertility drugs and retrieve immature eggs by using a needle. The immature eggs are then brought to maturity in glassware, after which concentrated sperm are added. After about 2 to 4 days, the embryos are ready to be transferred to the uterus of the woman, who is now in the secretory phase of her uterine cycle. If desired, the embryos can be tested for a genetic disease, and only those found to be free of disease will be used. If implantation is successful, development is normal and continues to term.
Gamete Intrafallopian Transfer (GIFT)
The term gamete refers to a sex cell, either a sperm or an egg. Gamete intrafallopian transfer (GIFT) was devised to overcome the low success rate (15–20%) of in vitro fertilization. The method is the same as in vitro fertilization, except the eggs and the sperm are placed in the uterine tubes immediately after they have been brought together. GIFT has the advantage of being a one-step procedure for the woman—the eggs are removed and reintroduced all at the same time. A variation on this procedure is to fertilize the eggs in the laboratory and then place the zygotes in the uterine tubes.
Surrogate Mothers
Some women are contracted and paid to have babies. These women are called surrogate mothers. The sperm and even the egg can be contributed by the contracting parents.
Intracytoplasmic Sperm Injection
In this highly sophisticated procedure, a single sperm is injected into an egg (Fig. 17.16). It is used effectively when a man has severe infertility problems.
Figure 17.16 Intracytoplasmic sperm injection. A microscope connected to a computer monitor is used to carry out intracytoplasmic sperm injection. A pipette holds the egg steady while a needle (not visible) introduces the sperm into the egg.
©Ideya/Shutterstock
CHECK YOUR PROGRESS 17.5
List the major forms of birth control in order of effectiveness.
Answer
Abstinence, vasectomy, tubal ligation, IUD, contraceptive implants, contraceptive injections, birth control pills, diaphragm, condoms, morning-after pills.
Explain why vasectomies and tubal ligations are permanent forms of birth control.
Answer
A vasectomy prevents sperm from entering the semen because the vas deferens is cut and the ends are sealed. Tubal ligation prevents the egg from moving through the uterine tubes because these tubes are severed and the ends are sealed. Reversing these surgeries is often unsuccessful.
Distinguish between an IVF and a GIFT procedure to compensate for infertility.
Answer
IVF conception occurs outside the body and the embryos are transferred to the uterus. In GIFT, the eggs and sperm are brought together and immediately placed in the uterine tubes.
CONNECTING THE CONCEPTS
For more information on the hormones presented in this section, refer to the following discussions:
Section 16.2 explains the role of the gonadotropic hormones.
Section 16.6 describes the hormones produced by the female reproductive system.
17.6 Sexually Transmitted DiseasesLEARNING OUTCOMES
Upon completion of this section, you should be able to
Distinguish between sexually transmitted diseases (STDs) caused by viruses and those caused by bacteria.
Describe the causes and treatments of selected STDs.
Sexually transmitted diseases (STDs), sometimes referred to as sexually transmitted infections (STIs), are caused by viruses, bacteria, fungi, and parasites.
STDs Caused by Viruses
Among STDs caused by viruses, effective treatment is available for AIDS (acquired immunodeficiency syndrome) and genital herpes. However, treatment for HIV/AIDS and genital herpes cannot presently eliminate the virus from the person’s body. Drugs used for treatment can merely slow replication of the viruses. Thus, neither viral disease is presently curable. Further, antiviral drugs have serious, debilitating side effects on the body.
HIV Infections
In Section 8.2, we explored the relationship between the HIV virus and AIDS, as well as some of the more common forms of treatment. At present, there is no vaccine to prevent an HIV infection (although several are in trials), nor is there a cure for AIDS. The best course of action is to follow the guidelines for preventing transmission of STDs outlined in the Health feature “Preventing Transmission of STDs” later in this section.
BIOLOGY TODAY HealthPreventing Transmission of STDsSexual Activities Transmit STDs
Abstain from sexual intercourse or develop a long-term monogamous (always the same partner) sexual relationship with a partner who is free of STDs (Fig. 17C).
Refrain from having multiple sex partners or having relations with someone who has multiple sex partners. If you have sex with two people and each of these has sex with two people, and so forth, the number of people who are relating is quite large.
Be aware that having relations with an intravenous drug user is risky, because the behavior of this group risks AIDS and hepatitis B. Be aware that anyone who already has another sexually transmitted disease is more susceptible to an HIV infection.
Avoid anal intercourse (in which the penis is inserted into the rectum), because this behavior increases the risk of an HIV infection. The lining of the rectum is thin, and infected CD4 T cells can easily enter the body there. Also, the rectum is supplied with many blood vessels, and insertion of the penis into the rectum is likely to cause tearing and bleeding that facilitate the entrance of HIV. The vaginal lining is thick and difficult to penetrate, but the lining of the uterus is only one cell thick at certain times of the month and does allow CD4 T cells to enter.
Uncircumcised males are more likely to become infected than circumcised males. This is because vaginal secretions, viruses, and bacteria may remain under the foreskin for a longer time.
Figure 17C Sexual activities transmit STDs.
(left): ©Igormakarov/Shutterstock; (right): ©Image Source/Getty Images
Practice Safer Sex
Always use a latex condom during sexual intercourse if you are not in a monogamous relationship. Be sure to follow the directions supplied by the manufacturer for the use of a condom. At one time, condom users were advised to use nonoxynol-9 in conjunction with a condom, but testing shows that this spermicide has no effect on viruses, including HIV.
Avoid fellatio (kissing and insertion of the penis into a partner’s mouth) and cunnilingus (kissing and insertion of the tongue into the vagina), because they may be a means of transmission. The mouth and gums often have cuts and sores that facilitate catching an STD.
Practice penile, vaginal, oral, and hand cleanliness. Be aware that hormonal contraceptives make the female genital tract receptive to the transmission of sexually transmitted diseases, including HIV.
Be cautious about using alcohol or any drug that may prevent you from being able to control your behavior.
Drug Use Transmits HIV
Stop, if necessary, or do not start the habit of injecting drugs into your veins. Be aware that HIV and hepatitis B can be spread by blood-to-blood contact.
Always use a new sterile needle for injection or one that has been cleaned in bleach if you are a drug user and cannot stop your behavior (Fig. 17D).
Figure 17D Sharing needles transmits STDs.
©Don Mason/Getty Images
Questions to Consider
Why might the use of female contraceptives actually increase the chances of contracting HIV?
Which cells in the blood act as a host for HIV?
The primary host for HIV is a helper T lymphocyte, or helper T cell (Fig. 17.17), although macrophages are also infected by the virus. The helper T cells are the very cells that stimulate an immune response (see Section 17.3), so loss of these cells causes the immune system to become severely impaired in persons with AIDS. During the first stage of an HIV infection, symptoms are Page 375few, but the individual is highly contagious. Several months to several years after infection, the helper T-lymphocyte count falls. Following this decrease, infections, such as other sexually transmitted diseases, begin to appear. In the last stage of infection, called AIDS, the helper T-cell count falls way below normal. At least one opportunistic infection is present. Such diseases have the opportunity to occur only because the immune system is severely weakened. Persons with AIDS typically die from an opportunistic disease, such as Pneumocystis pneumonia.
Figure 17.17 Cells infected by the HIV virus. HIV viruses (yellow) can infect helper T cells (blue), as well as macrophages, which work with helper T cells to stem the infection.
Source: National Institute of Allergy and Infectious Diseases (NIAID)/NIH/USHHS
How the HIV Infection Cycle Works
There is no cure for AIDS. A treatment called highly active antiretroviral therapy (HAART) is usually able to stop HIV reproduction to the extent that the virus becomes undetectable in the blood. The medications must be continued indefinitely, because as soon as HAART is discontinued, the virus rebounds.
Genital Warts
Genital warts are caused by the human papillomaviruses (HPVs). Many times, carriers either do not have any sign of warts or merely have flat lesions. When present, the warts commonly are seen on the penis and foreskin of men and near the vaginal opening in women. A newborn can become infected while passing through the birth canal.
Individuals currently infected with visible warts may have those growths removed by surgery, freezing, or burning with lasers or acids. However, visible warts that are removed may recur. A vaccine has been released for the human papillomaviruses that most commonly cause genital warts. This development is an extremely important step in the prevention of cancer, as well as in the prevention of warts themselves. Genital warts, and specifically the HIV virus, are associated with cancer of the cervix (see the chapter opener), as well as tumors of the vulva, vagina, anus, and penis. Researchers believe that these viruses may be involved in up to 90% of all cases of cancer of the cervix. HPV vaccinations, which are recommended for both women and men before the age of 26, might make such cancers a thing of the past.
Genital Herpes
Genital herpes is caused by herpes simplex virus. Type 1 usually causes cold sores and fever blisters, while type 2 more often causes genital herpes (Fig. 17.18).
Figure 17.18 Herpes simplex virus 2 and genital herpes. Several types of viruses are associated with herpes. Genital herpes is usually caused by herpes simplex virus 2. Symptoms of genital herpes include an outbreak of blisters, which can be present on the labia of females (a), or on the penis of males (b). c. A photomicrograph of cells infected with the herpes simplex virus.
(a): ©Bart’s Medical Library/Medical Images; (b): ©Biophoto Associates/Science Source; (c): ©David M. Phillips/Science Source
Persons usually get infected with herpes simplex virus 2 when they are adults. Some people exhibit no symptoms. Others may experience a tingling or itching sensation before blisters appear on the genitals. Once the blisters rupture, they leave painful ulcers, which may take between 5 days and 3 weeks to heal. The blisters may be accompanied by fever; pain on urination; swollen lymph nodes in the groin; and in women, a copious discharge. At this time, the individual has an increased risk of acquiring an HIV infection.
After the ulcers heal, the disease is only latent, and blisters can recur, although usually at less frequent intervals and with milder symptoms. Fever, stress, sunlight, and menstruation are associated with recurrence of symptoms. Exposure to herpes in the birth canal can cause an infection in the newborn, which leads to neurological disorders and even death. Birth by cesarean section prevents this possibility. There are antiviral drugs available that reduce the number and length of outbreaks. However, these drugs are not a cure for genital herpes. Latex or polyurethane condoms are recommended by the FDA to prevent the transmission of the virus to sexual partners.
Hepatitis
Hepatitis infects the liver and can lead to liver failure, liver cancer, and death. Six known viruses cause hepatitis, designated A, B, C, D, E, and G. Hepatitis A is usually acquired from sewage-contaminated drinking water, but this infection can also be sexually transmitted through oral-anal contact. Hepatitis B is spread through sexual contact and by blood-borne transmission (accidental needlestick on the job, receiving a contaminated blood transfusion, a drug abuser sharing infected needles while injecting drugs, from mother to fetus, etc.). Simultaneous infection with hepatitis B and HIV is common, because both share the same routes of transmission. Fortunately, a combined vaccine is available for hepatitis A and B. It is recommended that all children receive the vaccine to prevent infection, and that adults receive vaccinations throughout their lives (see Section 7.4). Hepatitis C (also called non-A, non-B hepatitis) causes most cases of posttransfusion hepatitis. Hepatitis D and G are sexually transmitted, and hepatitis E is acquired from contaminated water. Screening of blood and blood products can prevent transmission of hepatitis viruses during a transfusion. Proper water-treatment techniques can prevent contamination of drinking water.
STDs Caused by Bacteria
Only STDs caused by bacteria are curable with antibiotics. Antibiotic resistance acquired by these bacteria may require treatment with extremely strong drugs for an extended period to achieve a cure.Page 376
Chlamydia
Chlamydia is named for the tiny bacterium that causes it: Chlamydia trachomatis (Fig. 17.19). The incidence of new chlamydial infections has steadily increased since 1984.
Figure 17.19 Chlamydial infection. The different stages of a Chlamydia trachomatis infection inside a cell are stained red, brown, and black.
©Biomedical Imaging Unit, Southampton General Hospital/Science Source
Chlamydial infections of the lower reproductive tract are usually mild or asymptomatic, especially in women. About 18 to 21 days after infection, men may experience a mild burning sensation on urination and a mucoid discharge. Women may have a vaginal discharge, along with the symptoms of a urinary tract infection. Chlamydia also causes cervical ulcerations, which increase the risk of acquiring HIV.
If the infection is misdiagnosed or if a woman does not seek medical help, there is a particular risk of the infection spreading from the cervix to the uterine tubes, so that pelvic inflammatory disease (PID) results. This very painful condition can result in blockage of the uterine tubes, with the possibility of sterility and infertility. If a baby comes in contact with chlamydia during birth, inflammation of the eyes or pneumonia can result.
Gonorrhea
Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. Diagnosis in the male is not difficult, because typical symptoms are pain upon urination and a thick, greenish-yellow urethral discharge. In females, a latent infection leads to pelvic inflammatory disease (PID), which may result in damage to the uterus, ovaries, and other reproductive structures. If a baby is exposed during birth, an eye infection leading to blindness can result. All newborns are given eyedrops to prevent this possibility.
Gonorrhea proctitis, an infection of the anus characterized by anal pain and blood or pus in the feces, also occurs in patients. Oral-genital contact can cause infection of the mouth, throat, Page 378and tonsils. Gonorrhea can spread to internal parts of the body, causing heart damage or arthritis. If, by chance, the person touches infected genitals and then touches his or her eyes, a severe eye infection can result. Up to now, gonorrhea was curable by antibiotic therapy. However, resistance to antibiotics is becoming more and more common, and Neisseria gonorrhoeae is now classified as a “superbug,” meaning it has developed resistance to a variety of antibiotics.
Syphilis
Syphilis is caused by a bacterium called Treponema pallidum (Fig. 17.20). As with many other bacterial diseases, penicillin is an effective antibiotic. Syphilis has three stages, often separated by latent periods, during which the bacteria are resting before multiplying again. During the primary stage, a hard chancre (ulcerated sore with hard edges) indicates the site of infection. The chancre usually heals spontaneously, leaving little scarring. During the secondary stage, the victim breaks out in a rash that does not itch and is seen even on the palms of the hands and the soles of the feet. Hair loss and infectious gray patches on the mucous membranes may also occur. These symptoms disappear of their own accord.
Figure 17.20 Syphilis. Treponema pallidum, the cause of syphilis.
©Melba Photo Agency/Alamy
The tertiary stage lasts until the patient dies. During this stage, syphilis may affect the cardiovascular system by causing aneurysms, particularly in the aorta. In other instances, the disease may affect the nervous system, resulting in psychological disturbances. Also, gummas—large, destructive ulcers—may develop on the skin or within the internal organs.
Congenital syphilis is caused by syphilitic bacteria crossing the placenta. The child is born blind and/or with numerous anatomical malformations. Control of syphilis depends on prompt and adequate treatment of all new cases. Therefore, it is crucial for all sexual contacts to be traced so they can be treated. Diagnosis of syphilis can be made by blood tests or by microscopic examination of fluids from lesions.
SCIENCE IN YOUR LIFECan you catch an STD from a toilet seat?
When HIV/AIDS was first identified in the mid-1980s, many people were concerned about being infected by the virus on toilet seats. Toilet seats are plastic and inert, so they’re not very hospitable to disease-causing organisms. If you’re deciding on whether to hover or sit, remember that sitting on a toilet seat will not give you an STD.
Vaginal Infections
The term vaginitis is used to describe any vaginal infection or inflammation. It is the most commonly diagnosed gynecologic condition. Bacterial vaginosis (BV) is believed to cause 40–50% of the cases of vaginitis in the United States. Overgrowth of certain bacteria inhabiting the vagina causes vaginosis. A common culprit is the bacterium Gardnerella vaginosis. Overgrowth of this organism and subsequent symptoms can occur for nonsexual reasons. However, symptomless males can pass on the bacterium to women, who do experience symptoms.
The symptoms of BV are vaginal discharge that has a strong odor, a burning sensation during urination, and/or itching or pain in the vulva. Some women with BV have no signs of the infection. How women acquire these infections is not well understood. Having a new sex partner or multiple sex partners seems to increase the risk of getting BV, but females who are not sexually active get BV as well. Douching also appears to increase the incidence of BV. Women with BV are more susceptible to infection by other STDs, including HIV, herpes, chlamydia, and gonorrhea. Pregnant women with BV are at greater risk of premature delivery.
The yeast Candida albicans, and a protozoan, Trichomonas vaginalis, are two other causes of vaginitis. Candida albicans is normally found living in the vagina. Under certain circumstances, its growth increases above normal, causing vaginitis. For example, women taking birth control pills or antibiotics may be prone to yeast infections. Both can alter the normal balance of vaginal organisms, causing a yeast infection. A yeast infection causes a thick, white, curdlike vaginal discharge and is accompanied by itching of the vulva and/or vagina. Antifungal medications inserted into the vagina are used to treat yeast infections. Trichomoniasis, caused by Trichomonas vaginalis, affects both males and females. The urethra is usually the site of infection in males. Infected males are often asymptomatic and pass the parasite to their partner during sexual intercourse. Symptoms of trichomoniasis in females are a foul-smelling, yellow-green, frothy discharge and itching of the vulva/vagina. Having trichomoniasis greatly increases the risk of infection by HIV. Prescription drugs are used to treat trichomoniasis, but if one partner remains infected, reinfection will occur. It is recommended that both partners in a sexual relationship be treated and abstain from having sex until the treatment is completed.Page 379
CHECK YOUR PROGRESS 17.6
Explain which condition can occur due to a chlamydial or gonorrheal infection.
Answer
Pelvic inflammatory disease.
Identify a medical condition in women that is associated with genital warts.
Answer
Cancer of the cervix.
Discuss the causes of most STDs.
Answer
Viruses and bacteria transmitted by unprotected sex.
CONNECTING THE CONCEPTS
For more information on the topics presented in this section, refer to the following discussions:
Section 8.1 explores the structure of both viruses and bacteria.
Section 8.2 provides a detailed examination of the HIV virus, its replication, and the disease AIDS.
Section 8.4 examines how antibiotic resistance occurs and its consequences in the treatment of disease.
CONCLUSION
The good news for Ann is that early detection of cervical cancer is critical to successful treatment of the disease. For individuals with cervical cancer, the survival rate for those who have early detection is almost 100%, versus a less than 5% survival rate for those in whom the cancer has begun to spread, or metastasize, to other organs. In Ann’s case, her years of smoking cigarettes probably were a major factor in her development of cervical cancer. However, for many cases of cervical cancer, the cause is the human papillomavirus, or HPV. Over 15 forms of HPV have been linked to cervical cancers. In 2006, the Food and Drug Administration (FDA) approved an HPV vaccine for females. The vaccine is designed to be administered as three doses starting between the ages of 11 and 12 years. Recently, the vaccine was also approved for males ages 9 to 26 to prevent genital warts and to reduce the chances that men will transmit HPV to their sexual partners. With the development of the HPV vaccine, it is hoped that the rates of cervical cancer in women will drop drastically over the next few decades.
Key concepts to focus on • What is puberty? • How many chromosomes do body and sex cells each have? Why are they different? • What is mitosis and meiosis? • Know the functions of each structure in the male and female. • How do hormones play a role in the male? • Explain the ovarian and uterine cycles and the role of the specific hormones involved. • Where do fertilization and implantation occur? • Be able to discuss common birth control methods. • What is infertility? What can cause this? • What are some common sexually transmitted diseases? What are treatment options?
CONNECTING THE CONCEPTS
For more information on the topics presented in this section, refer to the following discussions:
Section 16.6 provides an introduction to the sex hormones.
Sections 19.3 and 19.4 examine the stages of mitosis and meiosis.
Section 19.5 compares the processes of mitosis and meiosis.
