Development of Foetus

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Development of Foetus
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Fertilisation
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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.

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CLEAVAGE
FERTILISATION
EMBRYONIC AREA
CHORION
EGG
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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.

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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.

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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

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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 its own immune
  system develops a few months after birth

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Harmful Transfer

• Thalidomide
• Alcohol
• Nicotine
• Heroin
• Rubella
• HIV

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Thalidomide

• 1950s 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!

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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.

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Foetal Alcohol Syndrome

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

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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.

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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.

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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.

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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.

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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.

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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

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Twins

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

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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 mothers blood becomes sensitised i.e. mother
  has produced antibodies.
• During a second pregnancy the mothers antibodies
  pass across the placenta and the blood
  agglutinates.

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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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