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Development of Foetus

Development of Foetus. Fertilisation. Cleavage. This is division of the zygote 36 hours after fertilisation. The number of cells doubles at each division and a solid ball of cells is formed. This develops into a hollow ball with a fluid-filled interior.

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Development of Foetus

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  1. Development of Foetus

  2. Fertilisation

  3. Cleavage • This is division of the zygote 36 hours after fertilisation. • The number of cells doubles at each division and a solid ball of cells is formed. • This develops into a hollow ball with a fluid-filled interior. • The cells at one side develops into the foetus (embryonic area) and the thin outer layer of cells is called the chorion.

  4. CLEAVAGE FERTILISATION EMBRYONIC AREA CHORION EGG

  5. Implantation • Occurs about 1 week after fertilisation. • The embryo attaches to the uterus wall. • Enzymes released by cells in the embryo digest part of the endometrium. • Finger-like projections eventually develop into part of the placenta. • The embryo is drawn into the endometrium and becomes surrounded. • Until the placenta develops, the embryo receives food and oxygen from the surrounding cells.

  6. Differentiation • This is the process by which unspecialised cells become specialised and carry out specific functions as part of tissues. • All cells contain the same genes but different genes are “switched on” in different cells which means many specialised cells are formed.

  7. The Placenta • This is a large disc with many villi which project into the uterus wall which has a rich supply of maternal blood. • The placental villi contain blood vessels rich in foetal blood. • Maternal and foetal blood does not mix but are close together so molecules can exchange freely

  8. Useful Transfer • Carbon dioxide diffuses from the foetal to maternal blood. • Oxygen diffuses from maternal to foetal blood. • Glucose moves from maternal to foetal blood by active transport. • Antibodies pass from maternal to foetal blood by pinocytosis meaning the baby acquires passive immunity to fight disease until it’s own immune system develops a few months after birth

  9. Harmful Transfer • Thalidomide • Alcohol • Nicotine • Heroin • Rubella • HIV

  10. Thalidomide • 1950’s drug used to combat morning sickness. • Caused limbs to fail to develop properly. • Also malformation of eyes, ears and heart together with mental disability and epilepsy. • No longer used!

  11. Alcohol • Excess alcohol during pregnancy can cause miscarriage. • Alcohol crosses placenta and blood vessels in umbilical cord can collapse temporarily causing a lack of oxygen to the baby needed for growing tissues and brain development. • Vitamins and minerals are not absorbed properly. • In extreme cases, foetus can suffer from foetal alcohol syndrome.

  12. Foetal Alcohol Syndrome • Pre- and post-natal growth problems. • Facial abnormalities. • Heart defects. • Development of abnormal joints and limbs. • Mental disabilities.

  13. Nicotine • Passes to foetus if mother smokes. • Cause growth problems for the foetus. • Carbon monoxide also passes to the foetus reducing the amount of oxygen in the blood. • Inadequate amounts of glucose reach foetal tissues. • Babies are smaller and do not develop intellectually at the same rate.

  14. Heroin • Foetus can also become addicted to heroine. • Vital processes slow down • When born, the baby is undersized and exhibits signs of withdrawal; muscle tremors, excessive perspiration and insomnia. • A programme of withdrawal is required under medical supervision.

  15. Rubella • If rubella (German measles) is contracted during the first few months of pregnancy it can cause the baby to be born with congenital (non-hereditary) birth defects which affect the ears,eyes and heart.

  16. HIV • If a pregnant mother is HIV positive the virus can pass across the placenta to the foetus. • This happens in about 30% of cases. • Most babies born with HIV develop AIDS and die at a young age.

  17. Placental Hormones • Placenta secretes oestrogen and progesterone which exhibit negative feedback control on the pituitary and inhibits the secretion of FSH and LH. • This ensures ovulation and menstruation does not occur during pregnancy.

  18. Mammary Glands • Oestrogen and progesterone stimulate proliferation of the milk-secreting tissues of the mammary glands. • This causes the breasts to increase in size and become prepared for lactation (milk production). • It is inhibited during pregnancy as it requires the activity of the hormone prolactin which is secreted following birth

  19. Twins • Monozygotic – genetically identical, originate from the same fertilised egg. • Dizygotic – non identical (genetically dissimilar), two eggs released and are fertilised by different sperm.

  20. Rhesus Factor • People who posses antigen D on their red blood cells are Rh+. • Those lacking the antigen are Rh-. • During birth, the foetal and mothers blood mixes. If the mother is Rh- and the foetus Rh+ • The mother’s blood becomes sensitised i.e. mother has produced antibodies. • During a second pregnancy the mother’s antibodies pass across the placenta and the blood agglutinates.

  21. HDNB This can be prevented by giving the mother and anti-D injection after the 1st child to destroy the antigens before antibodies are produced (antigens are destroyed).

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