Pregnancy

• The vagina receives an erect penis during sexual intercourse
• During sexual intercourse, sperms are ejaculated into the vagina
• There they begin to swim up to the oviducts
• If an ovum is released at this time it may be fertilised in the oviduct
• Although many sperms reach the ovum only one will fertilize it
• A membrane barrier is formed around the ovum to after fertilization to prevent other sperms from fertilising it
• The male and female nuclei join to form a zygote

Pregnancy at 40 weeks

• This zygote grows into an embryo 
• The sperm and ovum contributes 23 chromosomes each
• Chromosomes carry genes which determine the genetic structure of the child
• The zygote which is formed after fertilization starts to divide and soon becomes a ball of cells
• which moves down the oviduct towards the uterus
• It implants itself in the prepared lining of the uterus
• The developing embryo/foetus later develops a placenta
• The placenta separates  the mother’s blood from that of the developing baby
• Substances including carbon dioxide, oxygen and food diffuse in and out via the placenta
• These substances pass through the umbilical cord which connects the placenta to the developing foetus
• The embryo develops organs such as a heart and blood vessels
• At about 10 weeks the human foetus can be easily recognised with fingers, ears, toes and eyes
• A bag called the amnion grows around the foetus
• It is filled with amniotic fluid
• This fluid protects the baby from its mother’s bumps and falls
• The gestation period in humans is approximately 280 days/40 weeks/9 months

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