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Chapter 18: Life cycles and reproductive strategies

Chapter 18: Life cycles and reproductive strategies

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Chapter 18: Life cycles and reproductive strategies

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  1. Chapter 18: Life cycles and reproductive strategies Birth Control

  2. Birth Control • After intercourse, only a few hundred thousand of the millions of sperm ejaculated into the vagina will make it to the uterus. • Only a few hundred sperm will reach the ends of the Fallopian tubes. • Conception occurs in a Fallopian tube.

  3. Birth Control • An egg is capable of being fertilised for about two days after ovulation and sperm can last for about three days in the female reproductive tract. • There is about two to five days around ovulation (oestrus) where conception is most likely.

  4. Birth Control

  5. Birth Control

  6. Birth Control • The zygote takes about three to four days to travel down the Fallopian tube and be implanted in the uterus.

  7. Birth Control • Humans have practised birth control for thousands of years. • This is before our biological understanding of conception and embryology. • Ancient Egyptians placed foreign objects in the vagina to prevent the sperm entering the uterus.

  8. Birth Control • Contraception can be practised by women, men or couples. • Traditionally women have been responsible for birth control (most probably because they carry the consequences of failed contraception).

  9. Birth Control Today birth control falls into three categories: • Contraception (prevention of release of egg or sperm, blocking transport of egg or sperm, reducing the survival of sperm or preventing the transfer of sperm into the vagina). • Interference with implantation • Pregnancy termination (abortion)

  10. Birth Control Contraception • Most effective (apart from complete abstinence from sex) • Females - tubal ligation (cut and tie oviducts) • Males - vasectomy (cut and tie vas deferens)

  11. Tubal Ligation Top of uterus Fallopian tube Ovary

  12. Vasectomy

  13. Birth Control Contraception • The pill, diaphragm and condoms also effective • Small implants containing a hormone such as progesterone can last for up to three years

  14. Birth Control Contraception and interference with implantation • Intra-uterine device (IUD) is a flexible plastic device with copper wire wrapped around it. • The copper is toxic to sperm • IUDs also decrease the chance of implantation

  15. Birth Control Pregnancy termination • Surgical removal of embryo (termination or abortion) • Laws vary between states and countries