3. The fertilised egg divides and moves towards the uterus.
1. Ovulation An egg leaves the ovary and passes into the fallopian tube.
4. Implantation The embryo becomes lodged in the prepared lining of the uterus.
Sperm cells travel up from the vagina. Fig. 7 The location of ovulation, fertilisation and implantation.
13.9 Pregnancy
Embryo The developing baby in the uterus up to eight weeks.
It takes about five days for a fertilised egg to travel from the fallopian tube and implant in the uterus. Some people consider a woman to be pregnant from the moment of fertilisation while others think that pregnancy only begins with implantation. The average length of human pregnancy is 40 weeks. During this time, the embryo develops in the uterus, protected inside a bag of fluid called amniotic fluid. The amniotic fluid cushions the developing embryo.
Activity Model-making: The function of amniotic fluid
1. Fill a jar to the top with water and put an egg into it. 2. Close the lid tightly. 3. Shake it as hard as you can. What happens? 4. Remove the water and shake again. What happens? 5. What does this activity tell you about the function of amniotic fluid?
Placenta The structure linking the embryo to the lining of the uterus.
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A tube called the umbilical cord connects the embryo to the placenta. The placenta is rich in blood vessels. In the placenta, food and oxygen from the mother’s blood pass into the baby’s blood. Also, wastes such as carbon dioxide pass from the baby’s blood into the mother’s blood. The placenta allows the mother’s blood and the baby’s blood to get close enough to exchange gases, food and wastes but the bloods do not mix.
