Chapter 18: Life cycles and reproductive strategies Birth Control

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.

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.

Birth Control

Birth Control

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

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.

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).

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)

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)

Tubal Ligation Top of uterus Fallopian tube Ovary

Vasectomy

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

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

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