Foetal Development Flashcards

1
Q

What is a cordocentesis?

A

A cordocentesis is a procedure used to take a sample of fluid from the base of the umbilical cord.

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2
Q

List the events that occur in week 1 of gestation.

A

Week 1:

1 - Fertilisation.

2 - Blastocyst formation.

3 - Implantation.

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3
Q

What occurs in week 2 of gestation?

A

In week 2 of gestation, the bilaminar germ disc forms, comprising the epiblast and hypoblast.

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4
Q

What occurs in week 3 of gestation?

A

In week 3 of gestation, gastrulation occurs to form the trilaminar germ disc:

  • Endoderm – formed by epiblast cells that migrate through the primitive streak and displace the hypoblast cells.
  • Mesoderm – formed by epiblast cells that migrate through the primitive streak and lie between the epiblast layer and the newly created endoderm.
  • Ectoderm – formed by the epiblast cells that remain in position.
  • The hypoblast disappears.
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5
Q

What occurs in week 4 of gestation?

A

In week 4 of gestation, neurulation occurs (the transformation of the neural plate into the neural tube explain later in more detail).

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6
Q

List 2 tissues / organs that originate from the ectoderm.

A

The ectoderm gives rise to:

1 - The epidermis.

2 - Neural tissue.

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7
Q

List 5 tissues / organs that originate from the mesoderm.

A

The mesoderm gives rise to:

1 - Cardiac muscle.

2 - Skeletal muscle.

3 - Smooth muscle.

4 - Kidney tubules.

5 - Red blood cells.

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8
Q

List 6 tissues / organs that originate from the endoderm.

A

The endoderm gives rise to:

1 - Lungs.

2 - Thyroid gland.

3 - Pancreas.

4 - Liver.

5 - Colon.

6 - GIT.

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9
Q

How does the trilaminar disc fold to form a cylindrical embryo?

A
  • Cephalocaudal folding occurs in the longitudinal direction.
  • Lateral folding occurs in the lateral / transverse direction.
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10
Q

List the phases of foetal development (different to the phases of foetal growth as seen in the last lecture).

A

1 - Embryonic period (weeks 3-8):

  • Organogenesis.
  • Establishment of the main organ systems

2 - Foetogenesis (weeks 9-38):

  • Maturation and growth of tissues.
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11
Q

List the types of birth defect.

A

1 - Structural birth defect.

2 - Functional birth defect.

3 - Metabolic birth defect.

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12
Q

What is the difference between a malformation, disruption and deformation?

A
  • Malformation refers to abnormal formation of a structure.
  • Disruption refers to alterations to an already-formed structure due to an intrinsic destructive process.
  • Deformation refers to alterations to an already-formed structure due to an extrinsic mechanical factor.
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13
Q

What is the difference between a syndrome, association and sequence?

A
  • A syndrome is a group of abnormalities which tend to occur together with a specific known cause.
  • An association is a group of abnormalities which tend to occur together without a specific known cause.
  • A sequence is a cascade of abnormalities.
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14
Q

Which chromosome is affected in Down’s syndrome?

A

Down’s syndrome is caused by trisomy of chromosome 21.

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15
Q

List 6 features of Down’s syndrome.

A

1 - Congenital heart defects.

2 - Duodenal atresia (closure of the duodenum).

3 - Learning difficulties.

4 - Early onset Alzheimer’s.

5 - Single palmar crease.

6 - Wide sandal gap.

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16
Q

How does the trisomy occur in Down’s syndrome?

A
  • 94% of trisomy 21 is caused by nondisjunction.

- 6% of trisomy 21 is causes by robertsonian translocation.

17
Q

Define teratogen.

A

A teratogen is an agent that can predispose to a birth defect.

18
Q

List 6 teratogenic drugs.

A

1 - Alcohol.

2 - Cocaine.

3 - Thalidomide.

4 - Anticonvulsants.

5 - Antipsychotics.

6 - Warfarin.

19
Q

List 2 teratogenic infectious agents.

A

1 - Rubella.

2 - CMV.

20
Q

List 2 teratogenic maternal factors.

A

1 - SLE.

2 - Poorly controlled pre-existing DM.

21
Q

List 3 teratogenic mechanical factors.

A

1 - Malformed uterus.

2 - Oligohydramnios.

3 - Amniotic band syndrome.

22
Q

What is amniotic band syndrome?

A

Amniotic band syndrome is a birth defect in which bands of tissue in the amniotic sac tangle the foetus.

23
Q

How do teratogens affect foetal development at different points in development?

A
  • Prior to organogenesis, teratogens either cause miscarriage or have no effect.
  • Organogenesis is the period of greatest sensitivity to teratogens, and is where most birth defects arise.
  • During foetogenesis, the foetus is only significantly sensitive to functional birth defects.
24
Q

How does spina bifida arise?

A

Spina bifida arises from failure of closure of the caudal end of the neural tube.

*Anencephaly is caused by failure of closure of the rostral end of the neural tube.

25
Q

List the types of spina bifida.

What is the difference between each type?

A

1 - Spina bifida occulta (a bony defect in which no tissue extrudes from the spinal cord).

2 - Spina bifida meningocele (only the meninges extrude from the spinal cord).

3 - Spina bifida myelomeningocele (both the meninges and the neural tissue extrude from the spinal cord).

26
Q

What is the lemon sign?

A
  • The lemon sign refers to excessive concavity of the frontal bones seen on an ultrasound of the foetal skull.
  • It is a feature of spina bifida.
27
Q

What is the banana sign?

A
  • The banana sign refers to excessive curvature of the cerebellum seen on an ultrasound of the foetal skull.
  • It is a feature of spina bifida.
28
Q

How is spina bifida prevented?

A

Folic acid prevents spina bifida.

29
Q

How does cleft lip occur during development?

A
  • During development, the face has 5 prominences:

1 - 2x maxillary prominences.

2 - 2x mandibular prominences.

3 - 1x frontonasal prominence.

  • The frontonasal prominence develops invaginations, which become the nasal pits (precursors to the nostrils).
  • Lateral and medial nasal prominences develop around the nasal pits.
  • The maxillary prominences grow medially to merge with the medial nasal prominences.
  • Fissures form where the maxillary prominences grow into the medial nasal prominences. These fissures normally close to form the upper lip.
  • Failure of these fissures to close result in cleft lip.
30
Q

What is an omphalocele?

A
  • An omphalocele is an abdominal wall defect in which the abdominal viscera herniate into the umbilicus.
  • This results in a thin, transparent sac of amnion containing the abdominal contents protruding from the abdomen.
31
Q

What is gastroschisis?

A
  • Gastroschisis is an evisceration of the foetal intestine through the umbilicus.
  • The intestine is not contained within a sac as in an omphalocele.
32
Q

What is a nuchal translucency?

A
  • A nuchal translucency is a scan to measure the size of a fluid-filled subcutaneous space at the back of the head of the foetus.
  • A larger space indicates a higher risk of Down’s syndrome.
  • This is usually done in combination with blood markers.
33
Q

How does non-invasive prenatal testing work?

A
  • A sample of maternal blood is taken.
  • Foetal DNA is extracted from the maternal blood.
  • The DNA is used to test for genetic abnormalities.
34
Q

List 7 methods of prevention of pre-conception birth defects.

A

1 - Vaccination (e.g. Rubella).

2 - Avoidance of teratogenic substances.

3 - Folic acid supplements.

4 - Nutrition (e.g. iodine).

5 - Optimise disease control (e.g. diabetes).

6 - Maternal age.

7 - Prenatal testing.

35
Q

Which factors of the immune system of the mother must be balanced during pregnancy?

A

The mother’s immune tolerance to the foetus must be balanced with the protective ability to fight infections.

36
Q

List 6 mechanisms that contribute to the modulation of the maternal T cell response to the foetus.

A

1 - Reduced MHC expression of the trophoblast.

2 - FAS-ligand dependent deletion of local T cells.

3 - Induction of Th1 to Th2 shift by altered T cell cytokine production.

4 - Recruitment of Tregs.

5 - Hormonal immunomodulation.

6 - Deletion of foetal-specific T cells.