Reproduction in Humans (part 3): Sexual Intercourse, Fertilization & Pregnancy

1. Sexual Intercourse & Fertilization

2. Sex • when a male's erected penis is inserted into a female's vagina http://www.avert.org/cpills.htm

3. What causes pregnancy? • If a girl gets semen (the fluid released by a man's penis when he ejaculates) inside or even just around her vagina, this can make her pregnant • Because semen contains sperm • Pre-cum (the white liquid that leaks out of a man's erect penis before he ejaculates) can also contain sperm and therefore can also cause pregnancy Why?

5. Fertilisation Fusion of 2 haploid gametes Sperm trying to penetrate egg

7. Human Fertilization • The acrosome of sperms releases an enzyme to break down the corona radiata and disperse the follicle cells surrounding the egg • Only one sperm enters the egg (because as soon as the sperm has entered the egg, the membrane of the egg changes so that no other sperms can enter) • The remaining sperms die • The haploid sperm nucleus fuses with the haploid egg nucleus and a diploid zygote is formed

8. The process of fertilisation…

9. Development of the Embryo • The fertilised egg passes along the oviduct to the uterus • As it travels, it begins to divide to form a hollow ball of cells = embryo • It takes about 5 days to reach the uterus • Eventually the embryo sinks in and becomes embedded in the uterine lining = implantation

10. Fertilization and Implantaton 2. Fallopian tube Day 2 Day 3 Day 1 Day 4 Zygote 4 cells 2 cells Morula Fertilization Day 0 Blastocyst Day 7 *Days are not indicative of menstral cycle days. Implantation of blastocyst 1. 3. Uterine wall Egg released by ovary (DAY 0) Ovary

11. Implantation

13. Identifying the structures of the fetus in the uterus (worksheet)

14. 3. 1. 2. 4. 5. 6. 7. 8.

16. Development of the Embryo • Embryonic membranes develop to enclose the embryo • e.g. amnion (membrane)encloses the embryo in a fluid-filled space (amniotic fluid) called the amniotic cavity

17. Function of amniotic fluid • Supports and cushions the foetus before birth • Shock absorber • Protects the foetus against mechanical injury (as it is incompressible) • During birth, it lubricates and reduces friction in the vagina • It buoys up the foetus and allows it to move freely during growth

19. Development of the Embryo • Villi grow from the embryo into the uterine wall • Villi contain the blood capillaries of the embryo which come in close association with the mother’s blood • Villi + uterine wall in which villi are embedded = placenta

20. amnion

21. Placenta • The embryo is attached to the placenta by the umbilical cord which contains the blood vessels of the embryo namely: (i) 2 umbilical arteries (carry deoxygenated blood and waste from the foetus to the placenta) (ii) 1 umbilical vein (transports oxygenated blood and food substances from the placenta to the foetus)

24. Functions of the placenta • Allows dissolved food substances (e.g. glucose, a.a., mineral salts) and O2 to diffuse from the mother’s blood into that of the embryo • Allows metabolic products (e.g. urea + CO2) to diffuse from the embryonic blood capillaries into the mother’s bloodstream • Allows antibodies to diffuse from the mother’s blood into the embryonic capillaries. The antibodies protect the embryo against certain diseases • Produces progesterone which maintains the uterine lining in healthy state during pregnancy

26. Facts to note: • The blood system of the fetus is not continuous with mother’s blood system 1) If not the blood pressure of the mother would kill the embryo 2) The blood group of the embryo may not be the same as the mother’s and agglutination of the embryo’s blood could occur

28. Development of the Human Fetus 8th week of pregnancy foetus at week 20 sucking thumb

29. Timeline

30. How do twins come about?

31. TWINS!!! • Twins can either be identical (from one fertilised egg which then splits) or non-identical (from two separate eggs) • Identical twins have to be the same sex, as they have the same genes • Non-identical twins can either be the same sex or one of each http://www.pregnancycheck.com/pictures-of-pregnancy-stages.html

32. How twin pregnancies happen Identical twins • One egg splits after fertilization into two separate cells • Each one of these growing into a baby (usually sharing the same placenta) • Having developed from the same cell, they are always the same sex and look alike Non-identical or fraternal twins • Two eggs are fertilised by two different spermat the same time (each baby having its own placenta) • They can be different sexes and probably will not look any more alike than any brother or sister

33. Why Sex?

34. Why Sex? • Many people use sexual activity and intercourse as a way to express love, tenderness, and affection • However, emotional affection can also be expressed in alternative ways and this can circumvent many of the risks associated with intercourse • Enjoying a walk on the beach, a romantic dinner for two, or just a night at the movies can illustrate the same meaning inherent in sex and also allow for the formation of a deep emotional bond. • Refraining from sexual activity doesn't mean that you aren't interested in expressing affection for your loved one. • To the contrary, abstinence can open up opportunities to developing meaningful communication with your partner.

35. Why not sex? • Unlike other animals, humans are able to associate sexual behavior with their psychology and emotions • We are able to control our sexual urges and evaluate our decisions unlike the rest of the animal world • As a result, humans are able to engage in a relationship based on sexual fidelity • A lot of couples find that sexual behavior is more rewarding when explored in an atmosphere of deep commitment, and one in which the possibility of children may be explored • Not all men and women are prepared for such a commitment and thus choose to abstain from sex until they are in a monogamous relationship

36. You may live to regret it !!!

37. Men you should avoid

38. BE WARNED!!! But It Wasn't Really Sex, Was It?

39. Common Misconception • Some couples think they are practicing abstinence, while participating in variety of sexual activities • Oral sex, anal sex, mutual masturbation, and other similar activities do not qualify as abstinence • If you are involved in these practices, you are fooling yourself if you think you are not having sex • And most of these activities can still result in pregnancy and/or sexually transmitted disease

40. “Not-Really-Sex" Sexual Behavior • Mutual Masturbation: If semen gets anywhere near the vagina, the sperm can swim into the uterus, using the vaginal mucus as a conduit. That means if semen gets on someone's hands, and those hands get anywhere near the vagina, a pregnancy and/or STD can result. • Oral Sex: You can't get pregnant this way, but you can still contract a full compliment of nasty STDs. • Anal Sex: You can get pregnant this way as semen will drip out of the anus into the vaginal area. Also it's easier to contract an STD via anal sex as the anal tissue is more prone to tiny tears. • Sex with Your Clothes On: Sperm will swim right through clothing; this is why you will never find a condom made of cotton. • "But he just put it in half-way!" or "But he just put it in for a second!" or "But he pulled out before he came!": You are now having sexual intercourse using an ancient method of birth control called withdrawal. Every year one in five users of this method gets pregnant. STDs can also be spread by way of pre-ejaculate/vaginal fluids.

41. Abstinence – the best form of defence • everybody's first method of contraception • 100% effective in safeguarding against sexually transmitted diseases and pregnancy • However, sexual abstinence can be a hard thing to practice. • Young people especially find the drive of hormones and curiosity difficult to overcome. • If you want to practice abstinence, try avoiding high-pressure situations like empty dorm rooms and the back seat of automobiles. • Though it will be hard, you may find that abstinence is far more rewarding then you ever thought it could be