Human Conception and Pregnancy

1. Human Conception and Pregnancy How does a single cell become a fetus and then a baby?

2. Review… • Like most animals, humans reproduce sexually. • You started out as a single, fertilized egg called a zygote.

3. Surviving sperm use their flagella to swim through the uterus and up the fallopian tube. When they reach the egg, the sperm surround it. • They release an enzyme that breaks down the proteins in the egg’s outer covering. • As soon as a single sperm gets through that covering, a reaction occurs that keeps any other sperm from entering.

4. The membrane of the egg then fuses with the sperm. • Next, the sperm’s flagellum and mitochondria break down. • At that point, the sperm is only a nucleus. • This explains why all mitochondrial DNA is inherited from the mother.

5. When the sperm and egg nuclei fuse, fertilization is complete. • The fertilized egg then begins a 5 day journey down the fallopian tube (oviduct) toward the uterus. • During the journey, the zygote undergoes many divisions. • What type of division does it undergo? • By the time it reaches the uterus, it is an embryo that looks like a tiny ball of cells

6. 7B Human reproduction – Fertilisation Human reproduction begins with fertilisation.

7. The next step is called implantation. • In implantation, the tiny embryo becomes embedded in the lining of the mother’s uterus. • Implantation is successful only about 30 percent of the time. • http://health.howstuffworks.com/human-reproduction11.htm • Trimesters: Human pregnancy can be divided into three-month stages.

8. First Trimester 0- 3 • This lasts from fertilization to the end of the third month. • Once the embryo is implanted in the uterus, the placenta begins to grow. • What is the function of the placenta? • The placenta supplies food and oxygen from the mother’s blood to the developing embryo. • It contains a network of blood vessels that links the embryo to the mother. Waste from embryos blood diffuses into mothers blood

9. By the fourth week of pregnancy, the embryo is about 2-7 millimeters long. (500 times larger than fertilized egg) • The four chambered heart has formed • Brain becomes visible • Limb bud with tiny fingers and toes

10. By the end of the second month: cartilage is replaced by bone • Embryo is called fetus • most body parts formed • Arms and legs begin to move • Sucking reflex can be seen • What is the difference • Between an embryo and • A fetus?

11. http://videos.howstuffworks.com/discovery-health/6909-ultimate-guide-to-pregnancy-month-three-video.htmhttp://videos.howstuffworks.com/discovery-health/6909-ultimate-guide-to-pregnancy-month-three-video.htm • It is surrounded by a thin, protective membrane called the amnion. • Inside the amnion and surrounding the embryo, is amniotic fluid that protects the embryo from shocks. • The umbilical cord has also formed. • What is the function of the umbilical cord? • It contains arteries and veins that connect the embryo to the placenta. • It enters the embryo’s body at the umbilicus, or naval.

12. The blood of the mother and fetus do not mix together. • Oxygen and nutrients pass from the mother’s blood to the fetus through the placenta and umbilical cord. (smoking= bad) • Waste products like carbon dioxide pass from the fetus to the mother’s blood for removal.

13. Second Trimester 4-6 months • The 57-mm fetus moves enough for to be felt by the mother • All the organs have been formed • And like other mammals soft hairs cover the entire body • In the forth month the fetus begins to swallow amniotic fluid and hiccup and suck its thumb • In the 6th month eyelids and eyelashes form • Most cartilage in the skeleton has been replaced by bone

14. Third Trimester 7-9 months • The organ systems that developed in the 1st and second trimester will now function properly • All that remains will to increase body mass • http://health.howstuffworks.com/how-a-fetus-grows3.htm#

15. Birth • The mother goes through a series of contractions called parturition: the process of birth. • The cervix dialates and the amniotic membrane breaks (“water”) and lubricates the canal • The fetus is pushed, headfirst, through her vagina (birth canal). • The baby is still connected to the placenta by the umbilical cord. • When the doctor ties and cuts the umbilical cord, birth is complete.

16. Hormones and Birth • Hormones play a vital role in the birthing process • Relaxin is produced by the placenta= causes ligaments in the pelvis to loosen. This provides flexibility. • Prior to labour- the hormoneoxytocinis secreted by the pituitary gland • This causes strong uterine contractions which push the baby into the birth canal • After the placenta is expelled, secretion of estrogen and proesterone stops • If the mother does not breast feed her menstrual cycle begins within a few months

17. Create your own Chart!