1. Chapter 21: Reproductive System

2. Male Reproductive System
Genital Tract
In males the testes, held outside the body in the scrotum, produce sperm.
Sperm mature in coiled tubes atop each testis, called the epididymis (plural, epididymides).
At ejaculation, sperm leave the testes through the vas deferens (plural, vasa deferentia), and pass through the ejaculatory ducts to the urethra.
Sperm may be temporarily stored in the vas deferens before ejaculation.

3. Along the way, secretions (seminal fluid) are added from three glands: two seminal vesicles, the donut-shaped prostate gland at the base of the urinary bladder, and paired bulbourethral glands.
These glands add frustose for energy so sperm can swim, and prostaglandins that cause uterine contractions; the secretions are slightly basic.
Sperm with secretions from these glands is called semen.

4. 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. Circumcision is the removal of the foreskin. Notice that the penis in this diagram is not circumcised, because the foreskin is present. Table 21.1 (page 415) summarizes the organs of the male reproductive system and their functions.

5. Orgasm in Males
The penis, the organ of sexual, intercourse, becomes erect from sexual arousal that stimulates cGMP in smooth muscle cells to allow erectile tissue to fill with blood; arterioles dilate and veins are compressed.
Orgasm involves ejaculation and muscular tension followed by muscular contractions and relaxation.
Over 400 million sperm may be in each ejaculate.
Cyclic guanosine monophosphate is cGMP. During ejaculation, a sphincter closes off the bladder so that no urine enters the urethra.
Viagra inhibits an enzyme that breaks down cGMP, ensuring a full erection will take place. Erectile dysfunction (formerly referred to as impotency) occurs when the erectile tissue doesn’t expand enough to compress the veins.
Ejaculation occurs when sperm leave the penis in spurts.

6. Penis anatomy
Beneath the skin and connective tissue lies the urethra, surrounded by erectile tissue (on left). This tissue expands to form the glans penis, which in uncircumcised males is partially covered by the foreskin. On the right, the two columns of erectile tissue in the penis are located dorsally.

7. Male Gonads, the Testes
The testes, which produce sperm and male sex hormones, contain seminiferous tubules surrounded by interstitial cells.
Testes originate in the abdominal cavity but descend into the scrotum where it is cool enough for sperm development.
Testes that do not descend must be treated surgically otherwise sterility will result.

8. Seminiferous Tubules
Seminiferous tubules inside the testes produce haploid sperm through spermatogenesis.
Sustentacular cells (Sertoli cells) support, nourish, and regulate the cells during spermatogenesis.
Sperm have a head, middle piece, and tail.

9. Testes
The lobules of the testes contain seminiferous tubules. On the right, a light micrograph of the seminiferous tubules shows interstitial cells occurring in clumps among the seminiferous tubules.

10. The head of the sperm is covered by a cap called the acrosome which stores enzymes needed to penetrate the egg.
Sperm do not live more than 48 hours in the female genital tract.
Interstitial cells that lie between the seminiferous tubules within testes produce testosterone.

11. Sperm anatomy
A sperm has a head, a middle piece, and a tail. The nucleus is located in the head, which is capped by the acrosome containing enzymes.

12. Hormonal Regulation in Males
In both males and females, gonadotropin-releasing hormone, or GnRH, secreted by the hypothalamus stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
FSH stimulates the seminiferous tubules to produce sperm and the hormone inhibin.

13. LH stimulates interstitial cells to produce testosterone.
Testosterone brings about and maintains the male secondary sex characteristics.
Testosterone exerts feedback control over the hypothalamus and anterior pituitary resulting in a constant amount of hormones and sperm production over time.
Male secondary sex characteristics include broader shoulders, deeper voice, increased musculature, and hair on the face, chest, and other body regions.
Anabolic steroids resemble testosterone in their effects; however, health problems involving the kidneys, circulatory system, and hormonal balance, arise.

14. Hormonal control of testes
GnRH (gonadotropin-releasing hormone) stimulates the anterior pituitary to secrete the gonadotropic hormones: FSH stimulates the production of sperm, and LH stimulates the production of testosterone. Testosterone and inhibin exert negative feedback control over the hypothalamus and the anterior pituitary, and this regulates the level of testosterone in the blood.

15. Female Reproductive System
The female gonads are the ovaries.
The ovaries usually produce one egg (or ovum) per month during the process of oogenesis.
Ovulation is the release of the egg from the ovary as it enters an oviduct.

16. The Genital Tract
The oviducts that extend from the ovaries to the uterus have finger-like projections or fimbriae that sweep the egg into an oviduct with the help of cilia.
Fertilization usually takes place in the oviduct; the zygote moves by ciliary movement and oviduct contractions to the uterus, where it implants in the uterine lining (endometrium).

17. The pear-shaped uterus is thick-walled and muscular.
The lower end of the uterus is the cervix that opens into the vagina.
The vagina facilitates sexual intercourse, serves as the birth canal, and acts as an exit for menstrual flow.
A Pap test allows microscopic examination of the cervix tissue for cancer cells.
The endometrium has two layers – a basal layer and an inner, functional layer. In the nonpregnant female, the functional layer of the endometrium varies in thickness according to a monthly reproductive cycle called the uterine cycle.

18. The female reproductive tract
The ovaries release one egg a month; fertilization occurs in the oviduct, and development occurs in the uterus. The vagina is the birth canal as well as the organ of sexual intercourse.
Table 21.2 (page 418) lists the organs of the female reproductive tract along with their functions.

19. External Genitals
The external genital area of the female is the vulva and includes the vaginal opening, urethral opening, clitoris, labia minora, and labia majora.
The vagina may be partially closed by a ring of tissue called the hymen.
The reproductive and urinary systems in females are completely separate.

20. External genitals of the female
At birth, the opening of the vagina is partially blocked by a membrane called the hymen. Physical activities and sexual intercourse disrupt the hymen.

21. Orgasm in Females
Upon sexual stimulation, the labia, vaginal walls, and clitoris become engorged with blood.
The clitoris is extremely sensitive, and orgasm occurs at the height of the sexual response.
In contrast to the male penis, there is no refractory period, and multiple orgasms can occur during a single sexual experience.

22. The Ovarian Cycle Female Hormone Levels
An ovary has an outer cortex and an inner medulla; the cortex is where egg cells lie.
A female is born with up to 2 million ovarian follicles (with immature oocytes) that reduce to 300,000–400,000 by puberty, but only 400 follicles mature at the rate of one egg per monthly cycle.
The ovarian cycle is under the control of FSH and LH.

23. Anatomy of ovary and follicle
As a follicle matures, the oocyte enlarges and is surrounded by layers of follicular cells and fluid. Eventually, ovulation occurs, the mature follicle ruptures, and the secondary oocyte is released. A single follicle actually goes through all stages in one place within the ovary.
Primary follicles contain the oocyte and begin producing the sex hormone estrogen.
Secondary follicles contain the secondary oocyte and produce the sex hormones estrogen and some progesterone.
The vesicular (Graafian) follicle develops.
Ovulation: The secondary oocyte is released.
The corpus luteum produces the sex hormones progesterone and some estrogen.
The corpus luteum degenerates.

24. Egg follicles mature, from primary follicles to Graafian follicles.
When the egg is released, the empty follicle becomes the hormone-secreting corpus luteum.
The ovaries produce the female sex hormones estrogen and progesterone.
Estrogen and progesterone exert feedback control over the hypothalamus and the anterior pituitary causing the cycle to begin again.

25. Ovulation occurs on day 14 of a 28-day cycle.
During a follicular phase (day 1-13), FSH from the anterior pituitary stimulates development of an oocyte-containing follicle which secretes estrogen and progesterone.
Ovulation occurs on day 14 of a 28-day cycle.
During a luteal phase (days 15–28), the corpus luteum develops under the influence of LH and secretes progesterone and estrogen to promote the development of the endometrium.
As the luteal phase comes to an end, menstruation occurs.

26. Hormonal control of ovaries
The hypothalamus produces GnRH (gonadotropin-releasing hormone). GnRH stimulates the anterior pituitary to produce FSH (follicle-stimulating hormone) and LH (luteinizing hormone). FSH stimulates the follicle to produce estrogen, and LH stimulates the corpus luteum to produce progesterone. Estrogen and progesterone maintain the sexual organs (e.g., uterus) and the secondary sex characteristics, and exert feedback control over the hypothalamus and the anterior pituitary.

27. The Uterine Cycle
The female sex hormones, estrogen and progesterone, affect the endometrium, causing the uterus to undergo a cyclical series of events called the uterine cycle.
During menstruation (days 1-5), menses occurs due to the low levels of estrogen and progesterone in the blood.

28. During a proliferative phase (days 6-13), the endometrium thickens.
Ovulation occurs about day 14.
During a secretory phase (days 15-28), the endometrium continues to thicken and becomes vascular.
If pregnancy does not occur the cycle begins again.
Table 21.3 (page 422) summarizes the events of the ovarian and uterine cycles.

29. Female hormone levels
During the follicular phase of the ovarian cycle, 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. This structure produces increasing levels of progesterone, which causes the endometrial lining to become secretory. Menses due to the breakdown of the endometrium begins when progesterone production declines to a low level.

30. Fertilization and Pregnancy
If fertilization occurs, the embryo implants in the endometrium.
The placenta begins to produce human chorionic gonadotropin (HCG), which maintains the corpus luteum and the uterine lining is maintained.
Eventually, the placenta will produce sufficient estrogen and progesterone.
No new ovulations occur during this time.
The placenta originates from both fetal and maternal tissues.

31. Implantation
A scanning electron micrograph showing an embryo implanted in the endometrium on day 12 following fertilization.

32. Estrogen and Progesterone
At puberty, sex hormones (primarily estrogen) stimulate development of sex organs and maintain the secondary sex characteristics.
Estrogen is primarily responsible for female fat distribution.
Both estrogen and progesterone are needed for breast development.
Females have a wider pelvic girdle than males.

33. Menopause
Between the ages of 45 and 55, the ovarian and uterine cycles cease.
The ovaries are no longer responsive to anterior pituitary hormones, and thus no longer produce estrogen and progesterone.
When menstruation ceases for a year, menopause is complete.
Some women experience unpleasant symptoms during menopause, including hot flashes, insomnia, headaches, dizziness, and depression.

34. Control of Reproduction
Contraceptives are medications and devices that reduce the chance of pregnancy.
Birth Control Methods
Oral contraception (birth control pills) prevent ovulation by simulating pregnancy levels of estrogen and progesterone.
Table 21.4 (page 426) lists the most frequently used birth-control methods.

35. The intrauterine device (IUD) alters the uterine environment so fertilization and/or implantation cannot take place.
A diaphragm is a latex barrier that covers the cervix; a cervical cap is a mini-diaphragm.
The diaphragm must be used along with spermicidal jelly or cream.
The male condom is a latex sheath fitted over the erect penis.

36. Contraceptive implants use time-release progesterone, and Depo-Provera injections alter the endometrium to discourage pregnancy.
Contraceptive vaccines may be able to utilize the immune system to HCG that is necessary to maintain the embryo.
An antisperm vaccine may also be possible.

37. Various birth control devices
Oral contraception (birth control pills). b. Intrauterine device. c. Spermicidal jelly and diaphragm. d. Male condom. e. Contraceptive implants. f. Depo-Provera injection.

38. Morning-after Pills
A kit called Preven, made up of four synthetic progesterone pills, may be taken up to 72 hours after unprotected intercourse.
This upsets the normal uterine cycle, making implantation unlikely.
Mifepristone (RU-486) is a pill that causes the loss of an implanted embryo and may one day be routinely taken if menstruation is late.

39. Infertility
Infertility is the failure of a couple to achieve pregnancy after one year of regular, unprotected intercourse.
The American Medical Association estimates that 15% of all couples are infertile.
The cause of infertility can be attributed to the male (40%), the female (40%), or both (20%).

40. Causes of Infertility
Infertility in females is often caused by endometriosis, growth of the uterine lining outside the uterus, or blocked oviducts due to pelvic inflammatory disease (PID).
In males, a low sperm count and/or production of abnormal sperm occur due to disease, radiation, chemicals, high testes temperature, or psychoactive drugs.
Vasectomies are difficult to reverse, also leading to male infertility.
Endometriosis occurs when the menstrual discharge flows up into the oviducts and out into the abdominal cavity. This backward flow allows living uterine cells to establish themselves in the uterine cavity, where they go through the uterine cycle, causing pain and structural abnormalities that make it more difficult for a woman to conceive.
The success rate for vasectomy reversal is only about 40%.
Sometimes the causes of infertility can be corrected by giving the female fertility drugs, which are gonadotropic hormones that stimulate the ovaries and bring about ovulation. Such hormone treatments may cause multiple ovulations and higher-order multiple births.

41. Assisted Reproductive Technologies
Alternative methods to assist reproduction include artificial insemination by donor and intrauterine insemination, in vitro fertilization, and gamete intrafallopian transfer (GIFT), intracytoplasmic sperm injection, and surrogate mothers who carry a pregnancy for another couple.

42. Sexually Transmitted Diseases
Sexually transmitted diseases (STDs) are viral (AIDS, genital warts, genital herpes) or bacterial (gonorrhea, chlamydia, syphilis) in origin and are transmitted through sexual contact.
The STDs caused by bacteria can be treated with antibiotics, but those caused by viruses cannot.
The body does not become immune to STDs.

43. AIDS
Acquired immunodeficiency syndrome (AIDS) is caused by the retrovirus HIV whose primary host is helper T cells.
HIV attaches to a CD4 receptor in the host cell membrane; then the viral enzyme reverse transcriptase copies viral RNA into DNA, which integrates itself into a host chromosome.
At the time of viral reproduction, host DNA produces many copies of viral RNA and protein synthesis produces capsid proteins.

44. Reproduction of HIV
HIV is a retrovirus that utilizes reverse transcription to produce viral DNA. Viral DNA integrates into the cell’s chromosomes before it reproduces and buds from the cell.

45. Phases of an HIV Infection
During Category A: Acute Phase, the helper T lymphocyte count is 500 per mm3 or greater.
The immune system can still function normally and no serious symptoms appear.
The patient is highly infectious but does not have antibodies and therefore tests negative for HIV.

46. By the Category B: Chronic phase, the helper T cell count is 200–499 per mm3.
The lymph nodes are swollen, a person has severe fatigue, recurrent fevers, night sweats, and a persistent cough and diarrhea.
Toward the end of this phase, infections like thrush, and/or herpes simplex occur.

47. By the Category C: AIDS stage, the CD4 T cell count is below 200 per mm3.
Opportunistic infections develop, such as: Pneumocystis carinii pneumonia, Mycobacterium tuberculosis, toxoplasmosic encephalitis, Kaposi’s sarcoma, and invasive cervical cancer.
Treatment is successful for a while but death usually occurs 2–4 years following the AIDS stage.
Opportunistic infection is one that has the opportunity to occur only because the immune system is severely weakened.

48. The course of an AIDS infection
These photos show the effect of an HIV infection in one individual who progressed through all the stages of AIDS. On the left, AID patient Tom Moran is shown in July, In the center, Tom Moran is shown again, in early January On the right, Tom is shown in late January 1988.

49. Treatment for HIV
There is no cure for AIDS but highly active antiretroviral therapy (HAART), which combines the administration of two inhibitors of reverse transcriptase with a protease that prevents assembly, stops the progress of AIDS in the chronic stage for a number of years.
Research into various vaccine strategies is now being pursued.
The drug AZT is a reverse transcriptase inhibitor.
A pregnant woman who is infected with HIV and takes reverse transcriptase inhibitors during her pregnancy reduces the chance of HIV transmission to her newborn by nearly 66%.
Preventing the transmission of HIV is the subject of the Health Focus on page 432.

50. Genital Herpes
Genital herpes is caused by herpes simplex virus type 2 and occasionally type 1 which usually causes cold sore.
Blisters are followed by painful ulcers, which can clear up and reappear later.
Infants born vaginally to women with genital herpes may contract herpes, causing grave illness, blindness, neurological disorders, or death.
Pregnant women who have genital herpes are urged to deliver via cesarian section.

51. Genital herpes
A graph depicting the incidence of new reported cases of genital herpes in the United States from 1972 to 1998 is superimposed on a photomicrograph of cells infected with the herpesvirus.

52. Genital Warts
Genital warts are caused by human papillomaviruses (HPVs).
Warts need not be visible on penis or vaginal opening.
Genital warts are associated with cancer of cervix; teenagers with multiple sex partners are especially susceptible to cervical cancer.
Genital warts are not curable at this time.
A newborn can become infected during vaginal birth.
Efforts are underway to develop an effective vaccine for human papillomaviruses.

53. Genital warts
A graph depicting the incidence of new cases of genital warts reported in the United States from 1972 to 1998 superimposed on a photomicrograph of human papillomaviruses.

54. Hepatitis Infections There are a number of hepatitis infections.
Hepatitis A is normally acquired from drinking sewage-contaminated water, but may also be spread through oral/anal contact.
Hepatitis B is spread by sexual contact.
Hepatitis C is spread through transfusion.
Still other types of hepatitis are under investigation.

55. Hepatitis B
Hepatitis B virus (HBV) is more likely to be spread by sexual contact than the HIV virus.
Flu-like symptoms and jaundice may be present.
A chronic form of the disease can lead to liver failure.
An HBV vaccine is now available and a part of the routine immunizations for children.

56. Chlamydia
Chlamydia infections are more numerous than any other sexually transmitted disease.
Symptoms may appear to be a urinary tract infection with a mild burning sensation upon urination.
If not treated pelvic inflammatory disease (PID), sterility, or ectopic pregnancy can result.
If a newborn is exposed to chlamydia during delivery, inflammation of the eyes or pneumonia can result. It is possibl that chlamydial infections increase the possibility of premature births and stillbirths.

57. Chlamydial infection
A graph depicting the incidence of reported cases of chlamydia in the United States from 1984 to 1998 is superimposed on a photomicrograph of a cell containing different stages of the causative organism.

58. Detection and Treatment of Chlamydia
Tests for detection of chlamydia are expensive and may not be readily available.
Physicians can use several criteria aside from detection of the organism to decide whether to prescribe the proper antibiotics to cure chlamydia.
If gonorrhea is present, some physicians also routinely prescribe antibiotics for chlamydia.
About 40% of females and 20% of males with gonorrhea also have chlamydia.

59. Gonorrhea Gonorrhea is caused by the bacterium Neisseria gonorrhoeae.
Most males complain of pain on urination and there is a discharge.
Females are asymptomatic and may develop PID.
Infants can be infected during vaginal birth; silver nitrate or antibiotics in the eyes are standard treatment.

60. Gonorrhea
A graph depicting the incidence of new cases of gonorrhea in the United States from 1945 to 1998 is superimposed on a photomicrograph of a urethral discharge from an infected male. Gonorrheal bacteria (Neisseria gonorrhoeae) occur in pairs; for this reason, they are called diplococci.

61. Syphilis
Syphilis, caused by a bacterium Treponema pallidum, has three stages.
In the primary stage, a chancre forms at site of infection.
In the secondary stage, the individual breaks out in a rash that does not itch; hair loss and gray patches on the mucous membranes in the mouth may occur.
These symptoms soon disappear.

62. In the terminal tertiary stage, gummas (large destructive ulcers) may appear on skin and within internal organs, and the disease affects a wide variety of organs.
In congenital syphilis, in which the bacterium has crossed the placenta, the child is born blind and/or with anatomical malformations.
Antibiotics easily cure syphilis.

63. Two Other Infections
Vaginitis is caused by a naturally occurring yeast, Candida albicans, that grows to infectious levels.
Trichomoniasis is an vaginal infection caused by a flagellated protozoan.
The protozoan infection causes a white or yellow foul-smelling discharge, while the yeast causes a white, curdy discharge accompanied by itching.

64. Chapter Summary
The male reproductive system continuously produces a large number of sperm within a fluid medium.
The female reproductive system is designed for the monthly production of an egg and the preparation of the uterus to house the developing fetus.

65. Hormones control the monthly reproductive cycle in females and play a significant role in maintaining pregnancy when it occurs.
Birth-control measures vary widely in effectiveness.
Today, alternative methods of reproduction include in vitro fertilization, artificial insemination, and many others.
There are many serious sexually transmitted diseases and some are of epidemic proportions.