Paper Topic:

Pregnancy and Birth: Stages in the Life Cycle

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Growth and development

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Pregnancy as a stage of development

The birth of a new born is complex . The birth process involves a lot of processes . The first step involves conception . At conception , the sperm penetrates the uterine wall and fertilizes it . After fertilization , a zygote is formed . The zygote will prevent other sperms from penetrating the ova . Half of the zygotes chromosomes come from the ovary and half the spermatozoa . The zygote is alive and has the

necessary characteristics for growth and development . They include growth , reproduction and metabolism . If more than one egg is released and fertilized , the pregnancy involves two foetuses (twins . The twins are fraternal . Identical twins come about when one is fertilized then the egg separates into two embryos after its division

Eight days after fertilization , the blastocyst will attach to the uterine wall . The process is called implantation . Its wall is one cell thick . The inner cells develop into the embryo , and the outer cells get into the wall of the uterus developing into the placenta . The placenta will then secrete hormones that will help protect the pregnancy . The placenta transports oxygen and nutrients from mother to foetus . It also transports waste materials from foetus to mother

Some of the cells from the placenta develop into an outer layer of membranes (chorion ) surrounding the embryo . An inner layer of membranes (amnion ) develops by about day 10 to 12 , forming the amniotic sac . The amniotic sac fills...

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