CHAPTER 30 Summary

• The female reproductive system consists of paired ovaries, which produce eggs and secrete the hormones estrogen and progesterone, and accessory structures that enable fertilization and support pregnancy.
• The male reproductive system consists of paired testes, which produce sperm, the hormone testosterone, and accessory structures that enable fertilization.
• Fertilization of an egg by a sperm occurs in a female oviduct. Only one sperm can fertilize an egg at one time.
• The female reproductive cycle is coordinated by a complex balance of hormones that is controlled by the brain.
• Hormones from the hypothalamus trigger the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which in turn stimulate eggs to develop and the ovary to secrete estrogen and progesterone.
• Ovulation, the monthly release of an egg from an ovarian follicle, is caused by a spike in production of LH.
• Estrogen and progesterone stimulate eggs to develop and the endometrium to thicken and prepare for a possible pregnancy.
• Upon fertilization, the zygote divides and travels to the uterus, where it implants in the nutrient-rich endometrium.
• The implanted embryo secretes human chorionic gonadotropin hormone (hCG), which acts on the corpus luteum to maintain progesterone secretion.
• If an egg is not fertilized, progesterone levels fall and the endometrium sloughs off during menstruation.
• Sperm develop in the seminiferous tubules of the testes. The process is stimulated by testosterone.
• There are many approaches to contraception, including barriers between sperm and eggs and manipulation of reproductive hormones.
• Infertility has many causes, including blocked passageways caused by infection and scar tissue, genetic abnormalities, hormonal deficiencies, and advanced age.
• Assisted reproduction involves artificially bringing sperm and egg together, either inside the body (in IUI) or outside the body (in IVF).
• Fertility drugs increase the number of eggs that mature and are ovulated by a female at one time. Multiple pregnancies result when sperm fertilize more than one available egg.
• Humans and other mammals, as well as birds and reptiles, reproduce sexually using internal fertilization. Other sexually reproducing animals, such as fish, reproduce using external fertilization. Some organisms are asexual and have no sex at all.

• MORE TO EXPLORE

  • NBO News, Dateline (2009) http://www.nbcnews.com/id/29130147/ns/dateline_nbc-newsmakers/t/everything-i-do-revolves-around-my-children
  • American society for Reproductive Medicine http://reproductivefacts.org/
  • RESOLVE (national Infertility association) http://resolve.org/
  • Sunderam, s., et al. (2012) assisted reproductive technology surveillance—United states, 2009. Surveillance Summaries. Morbidity and Mortality Weekly Report 61(ss7):1–23 http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6107a1.htm
  • Mundy, L. (2008) Everything Conceivable: How the Science of Assisted Reproduction Is Changing Our World. New York: Anchor Books.