Analysing fertilisation and pregnancy

1. Fertilisation is the process whereby the sperm fuses with the ovum to form the zygote. It occur in the upper part of Fallopian tube.




2. Only one sperm is needed to fertilise the ovum.



3. 



























the journey of the sperms to the Fallopian tube

1. The rapid growth and development of a baby between the zygote stage and birth is called pregnancy.




2. The zygote undergoes cell division as it travels down the Fallopian tube towards the uterus.




3. The zygote forms a ball of cells and is referred to as embryo.




4. About seven days after fertilisation, the embryo embeds in the tissues of the uterus lining. This process is called implantation.

stages leading to implantation.

1. during this early stage of pregnancy, the embryo obtains ots nourishment from nutrients in the ovum and the uterus lining.



2. the sufaces of embryo and the uterus lining bind firmly to form a large disc called a placenta.



3. the job nutrishing the embryo is taken over by the placenta


4. by eight weeks after fertilisation, the developing embryo become clearly human and is called a foetus.


5. 
   

growth and development of the foetus in the uterus

1. at the placenta, the foetal and maternal blood vessel flow very close to each other but do not mix
2. the foetus is attached to the placenta by the umbilical cord
3. the umbilical cord has 2 blood vessels
4. an umbilical artery which carries carbon dioxide and other waste product from the foetus to the placenta
5. an umbilical vein carries blood containing oxygen and food from the placenta to the foetus.
6. oxygen, food, water and salts pass from the mother's blood into the foetal blood.
7. carbon dioxide and nitrogenous wates pass from the foetal blood into the mother's blood.
8. the foetus completely surrounded by a membrane called an amnion. the amnion is filled with the amniotic fluid
9. the amniotic fluid protects the embryo and later the foetus by cushioning it from physical damage
10. the time for the full development of a foetus forty weeks. this often called as gestation period.
11. in human beings, birth occurs in 3 main stages:

a) the expansion of the servix so that the baby's head can pass into the vagina

b) the strong contractions of the uterus which push the baby out of mother's body

c) further contractions of the uterus to expel the umbilical cord and placenta from mother's body.