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4.5 : Fertilization & Pregnancy Fertilization
• During sexual intercourse, sperms ejaculated into the vagina pass through the cervix into the uterus
• The sperms then swim up to the Fallopian tubes
• If an ovum is present in the Fallopian tube, the sperms surround the egg cell
4.5 : Fertilization & Pregnancy Fertilization • Only the head of
the sperm can break through the membrane of the ovum
• The tail is left outside
• Nucleus of sperm fuses with nucleus of ovum and forms a zygote
• Fertilization takes place in the Fallopian tube – Pregnancy begins
4.5 : Fertilization & Pregnancy Fertilization
• Cell division happens as the zygote moves down the Fallopian tube towards the uterus
• Zygote divides into two cells, then four and so on until it becomes a small ball of many cells called EMBRYO
4.5 : Fertilization & Pregnancy Implantation of the Embryo
• IMPLANTATION -Embryo attaches itself to the uterus wall with a placenta
• Placenta is connected to the embryo by the umbilical cord
• Embryo is surrounded & protected by 2 membranes containing fluid called amniotic fluid with the function : – Shock absorber & protects
the embryo – Buoys up the embryo so
that it can move freely
4.5 : Fertilization & Pregnancy Development of the Embryo into a Foetus
• Embryo has its own blood circulatory system – does not depend on the mother for blood supply
• Things that diffuse from mother’s blood capillaries into placenta : – Dissolved food – Hormones – Antibodies – Oxygen
4.5 : Fertilization & Pregnancy Development of the Embryo into a Foetus
• In the same way, waste products from embryo will diffuse into placenta then into mother’s blood capillaries
• Embryo continues grow in the uterus
• After 2 months : All main organs can be clearly seen – it’s called FOETUS
4.5 : Fertilization & Pregnancy Development of the Embryo into a Foetus
• About 4 ½ months, mother starts to feel the kick from foetus
• Before birth, foetus changes its position so that the head lies downwards
• About 9 months : Foetus is born which is then called a baby
• Gestation : The period from fertilization to birth
4.5 : Fertilization & Pregnancy Development of the Embryo into a Foetus
• During birth : – Uterus wall
contracts – Membranes
surrounding foetus break
– Cervix opens – Pushing force of
the mother together with the force of contraction of the uterus wall push the baby out through the vagina
4.5 : Fertilization & Pregnancy Development of the Embryo into a Foetus
• After birth, umbilical cord is tied in two places to prevent bleeding and then cut in between
• Placenta, umbilical cord & ruptured membranes associated with foetus are discharged automatically : aka AFTERBIRTH