BIOL 1030 Chapter 16 PDF

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Notes on the reproductive system...

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BIOL 1030 Ch 16 Reproductive System

Human Life Cycle The reproductive system is quite different in males and females. The reproductive organs (testes in males, ovaries in females) produce, nurture and transport the gametes, while the female allows the development of the fertilized egg within her body. Both testes and ovaries produce the sex hormones.

Mitosis and Meiosis Mitosis is duplication division. It is the type of cell division that takes place during growth and repair of tissues. Meiosis is reduction division. Meiosis takes place in the testes of males and ovaries of females during the production of gametes. During meiosis, the chromosome number is reduced from the normal 46 chromosomes, or 2n number, to 23 chromosomes, or n number.

Male Reproductive System In males, the testes produce sperm that mature in the epididymides and may be stored in the vasa deferentia before entering the urethra, along with secretions produced by seminal vesicles, the prostate gland, and bulbourethral glands.

The Penis and Male Orgasm The penis is the male organ of sexual intercourse. Circumcision is the surgical removal of the foreskin of the penis. During sexual arousal, spongy, erectile tissue in the penis becomes engorged with blood and the penis becomes erect. Erectile dysfunction is when the erectile tissue doesn't expand enough. Semen is ejaculated during male orgasm. This is followed by a refractory period during which stimulation does not bring about an erection. Male Gonads: the Testes The testes lie outside the abdominal cavity of the male within the scrotum. The scrotum helps regulate the temperature of the testes.

Seminiferous Tubules Spermatogenesis occurs within the seminiferous tubules. Sertoli cells support, nourish, and regulate the process of spermatogenesis. Mature sperm, or spermatozoa, have three distinct parts: a head, a middle piece, and a tail. The head is covered by a cap called the acrosome, which secretes enzymes needed to penetrate the egg. Interstitial Cells The male sex hormones are secreted by cells that lie between the seminiferous tubules. Therefore they are called interstitial cells.

Hormonal Regulation in Males Gonadotropin releasing hormone (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. LH stimulates interstitial cells to produce testosterone. Testosterone exerts feedback control over the hypothalamus and anterior pituitary resulting in a constant amount of hormones at all times. Testosterone is

responsible for the male secondary sex characteristics.

Female Reproductive System The female gonads are paired ovaries. The ovaries produce eggs and the female sex hormones.

The Genital Tract In females, an egg produced by an ovary enters an oviduct, which leads to the muscular uterus. At the lower end of the uterus, the cervix enters the vagina. The vagina is a tube that accepts the penis during intercourse, serves as the birth canal, and allows the menstrual flow to exit. A Pap test is an early detection test for cervical cancer. Development of the embryo and fetus normally takes place in the uterus. External Genitals The external genital area includes the vaginal opening, the clitoris, and the vulva consisting of the labia minora and the labia majora. Orgasm in Females Orgasm in females may be more subtle than male orgasm. The clitoris becomes erect and engorged with blood; release from muscular tension occurs in genitals and throughout the body.

The Ovarian Cycle Hormone levels cycle in the female on a monthly basis. The ovarian cycle drives the uterine cycle.

Ovarian Cycle: Nonpregnant Oogenesis occurs within the ovaries. The ovarian cycle consists of the development of the follicle, ovulation, and the development of a glandular corpus luteum.

Phases of the Ovarian Cycle During a follicular phase (day 1-13), FSH from 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 (day 15-28), the corpus luteum secretes progesterone and estrogen.

Estrogen and Progesterone The ovaries produce the female sex hormones estrogen and progesterone. Estrogen is largely responsible for the secondary sex characteristics in females. Menopause is the period in a woman's life during which the ovarian cycle ceases.

The Uterine Cycle: Nonpregnant Menstruation (days 1-5) occurs due to low levels of estrogen and progesterone in the blood. During a proliferative phase, (days 6-13) the endometrium thickens under the influence of estrogen. Ovulation occurs midcycle. During a secretory phase (days 15-28), the endometrium continues to thicken and becomes vascular under the influence of progesterone.

If pregnancy does not occur the cycle begins again. Fertilization and Pregnancy If fertilization occurs, the embryo embeds in the endometrium and the placenta begins to produce human chorionic gonadotropin (HCG), which prevents degeneration of the corpus luteum, and the uterine lining is maintained.

Control of Reproduction

Birth Control Methods Popular and effective means of birth control are oral contraceptive pills taken by the woman, and barrier methods (condoms, diaphragms) that are barriers to conception and offer some control over the transmission of sexually transmitted diseases. Contraceptive implants and injections are also available. Contraceptive vaccines are now being developed.

Vasectomy and Tubal Ligation Both vasectomy and tubal ligation are forms of sterilization. In a vasectomy the vas deferens are cut and sealed while in a tubal ligation the oviducts are cut and sealed.

Infertility Infertility is the failure of a couple to achieve pregnancy after one year of regular, unprotected intercourse. An estimated 15% of all couples in the United States are infertile.

Causes of Infertility Infertility can be caused by blocked oviducts (the result of pelvic inflammatory disease [PID] or endometriosis), by lack of regular ovulation, or by low sperm count or abnormal sperm in males. Many couples choose to adopt when they cannot conceive. Assisted Reproductive Technologies

Artificial Insemination by Donor (AID) Artificial insemination by donor (AID) involves inseminating the woman in the doctor's office, using sperm from a donor, from the woman's partner, or a combination of the two. In Vitro Fertilization (IVF) In vitro fertilization (IVF) is conception in lab glassware. Eggs are removed from the ovaries, sperm are added to them, and the eggs are placed in the woman's uterus after fertilization. Gamete Intrafallopian Transfer (GIFT) Gamete intrafallopian transfer (GIFT) is a means of removing a woman's eggs and placing them in the oviduct along with her husband's sperm. The advantages are lower cost and that it is a one-step procedure. Surrogate Mothers

Surrogate mothers are sometimes employed to bear children for women who, for various reasons, cannot. Intracytoplasmic Sperm Injection (ICSI) Intracytoplasmic sperm injection (ICSI) involves the injection of a single sperm cell into an egg.

Sexually Transmitted Diseases Sexually transmitted diseases (STDs) are caused by viruses, bacteria, protists, fungi, and parasites.

STDs Caused by Viruses Effective treatment is available for AIDS and genital herpes. Neither virus can be eliminated from the person's body, however.

HIV Infections The AIDS supplement discusses HIV infections at greater length. AIDS is the last stage of an HIV infection. Genital Warts Genital warts are caused by human papillomaviruses (HPVs). Researchers believe that these viruses may be involved in up to 90% of all cases of cancer of the cervix. Genital Herpes Genital herpes is caused by herpes simplex virus. Infection is often accompanied by blisters on the genitals. The disease is a latent one in which blisters can recur. Hepatitis Hepatitis infects the liver and can lead to liver failure, liver cancer, and death. Hepatitis B is spread through sexual contact as are hepatitis D and G.

STDs Caused by Bacteria Only STDs caused by bacteria are curable with antibiotics.

Chlamydia Chlamydia is named for the tiny bacterium that causes it. Initial infections are usually mild or asymptomatic. If the infection is not treated, the infection may spread from the cervix to the uterine tubes resulting in pelvic inflammatory disease (PID), a painful condition that can result in the blockage of the uterine tubes. Gonorrhea A latent infection can result in PID and can cause sterility in males as well. Gonorrhea can spread to internal parts of the body causing heart damage or arthritis. Syphilis Syphilis has three stages often separated by latent periods. During the primary stage, a hard chancre indicates the site of infection. The secondary stage is characterized by

a rash, while during the tertiary stage, syphilis may affect the cardiovascular system and nervous system.

Vaginal Infections Bacterial vaginitis/vaginosis can be due to bacterial, protozoan, or yeast infections. The protozoan Trichomonas vaginalis or the yeast Candida albicans can both be responsible....