Reproductive System

Drawing of the female reproductive system. Source: SEER's Training Web Site.

Drawing of the male reproductive system. Source: SEER's Training Web Site.

The reproductive system is a group of organs whose purpose is to allow procreation (the process which allows two living beings to produce a third, separate being). Reproduction is necessary for the continuation of a species, and allows genetic material to pass from one generation to another. Unlike any other system in the human body, the male and female reproductive systems are complementary to one another.

Other Names

• Genitalia

Types

The male and female reproductive systems are separate and unique but work together to allow reproduction.

Female reproductive system

The female reproductive system includes the ovaries, Fallopian tubes, uterus, vagina, accessory glands, external genital organs, and the mammary glands. The external genitalia are the accessory structures of the female reproductive system that are external to the vagina. They are also referred to as the vulva or pudendum. The external genitalia include the labia majora, mons pubis, labia minora, clitoris, and glands within the vestibule. The female reproductive system contributes to fertilization as well as maintaining the developing fetus, birth and nursing.

Male reproductive system

The male reproductive system, like that of the female, consists of those organs whose function is to produce a new individual—to accomplish reproduction. This system consists of a pair of testes and a network of excretory ducts (epididymes, vas deferens, and ejaculatory ducts), seminal vesicles, the prostate, the bulbourethral glands, and the penis. The seminal vesicles, prostate gland, and the bulbourethral glands are the accessory glands of the male reproductive system. These glands secrete fluids that enter the urethra. The male reproductive system is primarily on the outside of the body (external), as opposed to the female system which is mostly inside the pelvis (internal).

Description

The reproductive system is divided into the primary and secondary, or accessory, reproductive organs. The primary reproductive organs, or gonads, consist of the ovaries and testes. These organs are responsible for producing the egg and sperm cells (gametes), and for producing hormones. These hormones function in the maturation of the reproductive system and the development of sexual characteristics. The hormones also have important roles in regulating the normal physiology of the reproductive system. All other organs, ducts, and glands in the reproductive system are considered secondary, or accessory, reproductive organs. These structures transport and sustain the gametes and nurture the developing offspring.

Role of the Reproductive System in the Body

The major function of the reproductive system is to ensure survival of the species. Other systems in the body, such as the endocrine and urinary systems, work continuously to maintain homeostasis (a stable internal environment) for survival of the individual. An individual may live a long, healthy, and happy life without producing offspring, but if the species is to continue, at least some individuals must produce offspring.

Within the context of producing offspring, the reproductive system has four functions:

• To produce egg and sperm cells
• To transport and sustain these cells
• To nurture the developing offspring
• To produce hormones

How the Reproductive System Works

Female reproductive system

The organs of the female reproductive system do the following:

• Produce and sustain the female sex cells (egg cells or ova)
• Transport these cells to a site where they may be fertilized by sperm
• Provide a favorable environment for the developing fetus
• Move the fetus to the outside at the end of the development period
• Produce the female sex hormones.

The female sexual response includes arousal and orgasm, but there is no ejaculation. A woman may become pregnant without having an orgasm.

Follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone have major roles in regulating the functions of the female reproductive system. At puberty, when the ovaries and uterus are mature enough to respond to hormonal stimulation, certain stimuli cause the hypothalamus to start secreting gonadotropin-releasing hormone. This hormone enters the blood and goes to the pituitary gland, where it stimulates the secretion of follicle-stimulating hormone and luteinizing hormone. These hormones, in turn, affect the ovaries and uterus and the monthly cycles begin. A woman's reproductive cycles last from menarche to menopause.

The monthly ovarian cycle begins with the follicle development during the follicular phase, continues with ovulation during the ovulatory phase, and concludes with the development and regression of the corpus luteum during the luteal phase.

The uterine cycle takes place simultaneously with the ovarian cycle. The uterine cycle begins with menstruation during the menstrual phase, continues with repair of the endometrium during the proliferative phase, and ends with the growth of glands and blood vessels during the secretory phase.

Menopause occurs when a woman's reproductive cycles stop. This period is marked by decreased levels of ovarian hormones and increased levels of pituitary follicle-stimulating hormone and luteinizing hormone. The changing hormone levels are responsible for the symptoms associated with menopause.

Male reproductive system

Sperm are produced in the testicles. Sperm cells pass through a series of ducts to reach the outside of the body. After they leave the testicles, the sperm passes through the epididymis, ductus deferens, ejaculatory duct, and urethra.

Seminal fluid, or semen, is a slightly alkaline mixture of sperm cells and secretions from the accessory glands. Secretions from the seminal vesicles make up about 60% of the volume of the semen, with most of the remainder coming from the prostate gland. The sperm and secretions from the bulbourethral gland contribute only a small volume.

The volume of semen in a single ejaculation may vary from 1.5 to 6.0 ml. There are usually between 50 to 150 million sperm per milliliter of semen. Sperm counts below 10 to 20 million per milliliter usually present fertility problems. Although only one sperm actually penetrates and fertilizes the ovum, it takes several million sperm in an ejaculation to ensure that fertilization will take place.

The male sexual response includes erection and orgasm accompanied by ejaculation of semen. Orgasm is followed by a variable time period during which it is not possible to achieve another erection.

Three hormones are the principle regulators of the male reproductive system. Follicle-stimulating hormone (FSH) stimulates spermatogenesis (the creation of sperm); luteinizing hormone (LH) stimulates the production of testosterone; and testosterone stimulates the development of male secondary sex characteristics and spermatogenesis.

Diseases of the Reproductive System

Some diseases that directly involve the reproductive system are the following:

• Benign prostatic hyperplasia
• Cancer
  • Cervical cancer
  • Prostate cancer
  • Uterine cancer
  • Vaginal cancer
• Cryptorchidism
• Disorders of sexual differentiation
• Ectopic pregnancy
• Endometriosis
• Hypogonadism
• Infertility
• Pelvic inflammatory disease
• Peyronie disease
• Premenstrual syndrome
• Sexually transmitted diseases

Diseases of the body that are associated with problems in the reproductive system, along with other symptoms elsewhere in the body, include these:

• Cystic fibrosis
• Klinefelter syndrome
• Turner syndrome

Symptoms

Symptoms indicating that there may be a problem in the reproductive system include the following:

• Infertility
• Impotence
• Menorrhagia (heavy menstrual bleeding)
• Pelvic pain
• Urethritis

Procedures

Some procedures that may be done to diagnose problems with the reproductive system include:

• Hysteroscopy
• Pap smear

Surgery

Some types of surgery that are done on the reproductive system are the following:

• Hysterectomy
• Tubal ligation
• Vasectomy

Related Professions

• An obstetrician/gynecologist is a physician trained in providing medical and surgical care to women for issues related to their reproductive systems.
• A urologist is a physician who is trained to provide medical and surgical care for the urinary tract of men and women and the reproductive tract in men.
• A midwife is a person specially trained in providing care to women throughout pregnancy, delivery, and postpartum.
• A reproductive endocrinologist is a physician trained to provide medical and surgical care to women with diseases involving the reproductive system.

History

The introduction of birth control pills, intrauterine devices, and vasectomy in the 1960s led to a newfound sexual liberation, as couples were now able to have intercourse with a near 100% ability to avoid a subsequent pregnancy. The ability to prevent pregnancy has been theorized to have directly contributed to women's liberation and to the spread of sexually transmitted diseases, particularly HIV/AIDS.^[1]

Research

Recent discoveries

• Multiple studies have been done to determine whether pesticides affect sperm quality. A review of these studies shows that there are numerous ways pesticides may affect reproduction and suggests that pesticides probably do have a negative effect on sperm. The author cautions that further studies are needed, however.^[2]
• The use of low-dose testosterone to improve libido in postmenopausal female cancer survivors was recently studied. ^[3]
• A recently completed study examined the regulation of reproductive hormones in adult men. The National Institute of Child Health and Human Development looked at the role that testosterone and estradiol play in controlling the release of LH (lutenizing hormone) and FSH (follicle stimulating hormone). Testosterone and estradiol come from the testes, and LH and FSH are released from the pituitary gland. ^[4]
• The reproductive effects of chemicals such as pesticides and PCBs, that are thought to act on hormones like estrogen, was studied. A population of Laotian immigrants was evaluated, as this group was thought to have a higher exposure to the chemicals, possibly from their homeland or from ingested fish caught in the San Francisco bay. ^[5]

Future research

• An ongoing study is reviewing the use of the contraceptive levonorgestrel intrauterine system (LNG IUS) as hormone replacement therapy (HRT) in post-menopausal women. ^[6]
• The National Cancer Institute is conducting a follow-up study on daughters and sons of women who were given diethylstilbestrol (DES) in pregnancy. DES, primarily used to treat morning sickness, was believed to cause reproductive dysfunction and a type of reproductive cancer (vaginal clear cell adenocarcinoma (CCA)) ^[7]

References

1. ↑ William P. Didusch Center for Urologic History Web site. Sexuality: Perception and Performance Throughout History. PDF.
2. ↑ Perry MJ. Effects of environmental and occupational pesticide exposure on human sperm: a systematic review. Hum Reprod Update. 2008 May-Jun;14(3):233-42. Epub 2008 Feb 15. Abstract | Full Text
3. ↑ ClinicalTrials.gov. Low-Dose Testosterone in Improving Libido in Postmenopausal Female Cancer Survivors
4. ↑ ClinicalTrials.gov. Investigating the Regulation of Reproductive Hormones in Adult Men
5. ↑ ClinicalTrials.gov. Reproductive Effects of Pesticide, PCB and Mercury Exposure in Laotian Immigrants
6. ↑ ClinicalTrials.gov. Assessment of the Transfer of Using Levonorgestrel Intrauterine System (LNG IUS) as a Contraceptive to Using it as Part of Hormone Replacement Therapy (HRT).
7. ↑ ClinicalTrials.gov. Continuation of Follow-up of DES-Exposed Cohorts

External Links

American College of Nurse-Midwives

American College of Obstetricians and Gynecologists

American Urological Association

• UrologyHealth.org: A patient information Web site.

Society for Reproductive Endocrinology and Infertility