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MBD > Mechanisms of Disease During Embryogenesis* > Flashcards

Mechanisms of Disease During Embryogenesis* Flashcards

1
Q

What are the 2 main periods in human development?

A
  • Embryonic period
  • Fetal period
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2
Q

What is the embryonic period?

A
  • Period up to the end of week 8
  • Most of the organogenesis occurs in these first 8 weeks
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3
Q

What is the fetal period?

A
  • The remaining time in utero following the embryonic period (up to week 8)
  • Involves growth and modelling
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4
Q

What can defects during embryogenesis result in?

A

Defects during embryogenesis result in congenital malformations

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5
Q

What are the mechanisms of development an egg goes through to develop into an adult?

A

From egg → fertilization → cleavage → gastrulation → neurulation and somitogenesis → organogenesis → adult

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6
Q

Where does fertilisation occur?

A

In the fallopian duct (ampullary region)

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7
Q

What must happen before the development of the embryo proper?

A
  • Conceptus must first implant, then generate the “germ” disc.
  • This takes ~10 days.
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8
Q

What is the 16-cell zygote known as?

A

Morula

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9
Q

When does cleavage occur?

A
  • `Cleavage occurs when zygote is moving from the site of fertilisation to the uterus
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10
Q

What is compaction?

A
  • Morphogenic process
  • The trophoblast secretes fluid inside, forming a blastocoele that pushes the inner cell mass to one side
    • Inner cell mass splits into the hypoblast and the epiblast
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11
Q

In the morula, which cells are polar and what are their poles called?

A
  • Trophoblast cells have an apical and a basolateral surface
  • Inner cell mass are apolar
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12
Q

How can you describe the cells inside the embryo following compaction?

A
  • The cells inside the embryo are apolar
  • All their sites are in contact with other sites; they don’t have any surface that is free
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13
Q

Blastocoele?

A

Fluid filled space secreted by trophoblast

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14
Q

Blastocyst?

A

Formed when trophoblast has secreted the blastocoele and pushed the inner cell mass to the side

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15
Q

What does the inner cell mass split into?

A

Hypoblast and Epiblast

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16
Q

Which part of the epiblast is touching the blastocoele?

A

Hypoblast

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17
Q

What happens once the embryo is fully implanted?

A

Formation of the bilaminar germ disk

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18
Q

What happens to the cells following compaction?

A
  • The cells on the outside give rise to the TROPHECTODERM
  • Cells on the inside give rise to the inner cell mass.
  • The outside cells start pumping fluid to the inside of the embryo which leads to the formation of a fluid filled cavity inside the embryo called the BLASTOCOELE.
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19
Q

Blastocyst?

A
  • The Blastocoele pushes the inner cell mass towards one side and gives an asymmetry to the embryo.
  • Embryo has divided into 32-64 cells, (usually day 4/5) and now called a BLASTOCYST
  • The blastocyst by now has reached the uterus and is ready to implant in the uterine wall.
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20
Q

At the uterus, what happens on day 6/7?

A
  • The 2nd cell fate is established, inner cell mass cells give rise to 2 cell types:
    • Hypoblast
    • Epiblast
  • After implantation, you can see the bilaminar germ disk, composed of epiblast and hypoblast.
  • Epiblast cells arrange in a way that gives rise to the Amniotic Cavity
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21
Q

Gastrulation?

A
  • Gastrulation is the process where the bilaminar embryonic disc (consisting of the hypoblast and epiblast) undergoes reorganisation to form a trilaminar disc (3 primary germ layers)
  • Leads to the formation of 3 layers of cells (from 2 layers).
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22
Q

How are the different layers formed in gastrulation?

A
  • Hypoblast (primitive endoderm) is displaced by involuting cells that become definitive Endoderm (the endoderm is responsible for the formation of the GI tract)
  • The remaining cells of the epiblast are called the Ectoderm
  • Cells that remain in the space between the definitive endoderm and definitive ectoderm form a layer called the Mesoderm.
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23
Q

What is another name for the hypoblast?

A

Primitive endoderm

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24
Q

During gastrulation what displaces the hypoblast>

A

Involuting cells that become the definitive endoderm and mesoderm

25
Q

What happens following gastrulation?

A

ECTODERM, ENDODERM and MESODERM have all be formed
So now there are all 3 layers and ready for NEURULATION.

26
Q

Define neuralation

A

The folding process in vertebrate embryos which includes the transformation of the neural plate into the neural tube.

27
Q

What happens when the primitive streak reaches the other end of the epiblast?

A

it regresses

28
Q

Where does the mesoderm form?

A

Between the epidermis and the hypoblast

29
Q

What does the epiblast form?

A

Ectoderm

30
Q

What is the notochord?

A

A rod of cells that secrete molecules extracellularly that instruct the exoderm on top of it to become neural tissue

31
Q

How is the notochord formed?

A

Regression of the primitive streak

32
Q

What forms the neural plate?

A

Notochord sections

33
Q

How is the neural tube formed?

A
  • Folding of the neural plate
  • Closure starts at edge between hindbrain and spinal cord, then progresses anteriorly and posteriorly till the neural tube is fully closed.
34
Q

Where is the neural tube found>

A

Covered by the surface ectoderm, buried in the embryo

35
Q

Where does formation of the neural tube start?

A

From the middle and moves out towards the edges?

36
Q

What does the ectoderm form?

A

Specification of the CNS

37
Q

What does the mesoderm organise into?

A

Blocks called somites

38
Q

What are somites precursors to?

A

Muscles and bones etc

39
Q

What does folding of the embryo form?

A

Umbilical cord

40
Q

What happens simulatenously to neuralation and somitogenis?

A
  • Formation of the gut
  • Body folding
41
Q

What is neurulation is concomitant with?

A
  • Neurulation is concomitant with other form-shaping (morphogenetic) processes
  • Particulatly gut formation and body folding (“silk purse” model) to develop from flat embryo to a folded embryo.
42
Q

What is the ‘cloth purse’ model?

A
  • Septum and heart move from margin to centre
  • Yolk sac, allantois and stalk make umbilical cord
43
Q

What delimits the gut tube?

A

Prochordal and cloacal plates delimit gut tube.

44
Q

Folding occurs in what 2 planes?

A

Folding occurs in 2 planes, horizontal and median plane, result of differing rates of growth of embryonic structures.

  • Folding in horizontal plane → 2 lateral body folds
  • Folding in median plane → cranial and caudal folds
  • Folding takes place simultaneously.
45
Q

What happens to folding during 4/5th weeks?

A
  • Endoderm moves towards midline and fuses incorporating the dorsal part of the yolk sac creating primitive gut tube which differentiates into foregut, midgut, hindgut.
  • Foregut (found at cranial end) is covered by oropharyngeal membrane which at 4 weeks ruptures to form the mouth.
  • Connection to yolk sac narrows to a thin stalk called Vitelline duct.
46
Q

What does folding result in?

A

Folding results in formation of umbilical cord and formation of the gut.

47
Q

What happens during the 7th week?

A

cloacal membrane ruptures to form urogenital and anal opening.

48
Q

What happens if something goes wrong in embryogenesis?

A
  • If something goes wrong in first 8 weeks of embryogenesis, can result in severe malformations in organ systems.
  • Defects in first 2 weeks leads to complete death of embryo.
  • Later than 8 weeks, can have malformations that have deleterious effects in later life.
49
Q

What are the desirable characteristics of a model organism?

A

We cannot study embryos in detail so use other animal models.

  • Relevance/representative – learn things from an organism that help us understand human embryonic development.
  • Accessibility/availability
  • Experimental manipulation
  • Genetics – genome is fully sequenced so we can manipulate it.
  • Cost/space
50
Q

What occurs in Organogenesis?

A
  • Differentiation of somitic derivatives
  • Development of sensory organs
  • Limb formation
  • Formation of face structures
  • Formation of genital structures
51
Q

Differentiation of somitic derivatives

A

bones, muscles, tendons

52
Q

Development of sensory organs

A

ears, eyes, olfactory pits

53
Q

Limb formation

A
  • forelimbs first, hindlimbs next
  • establishment of pattern in the limbs:
    • proximodistal, anterior-posterior, dorsal-ventral
54
Q

Classification of causes of disease(?)

A
  • Single gene mutations
  • Chromosomal anomalies
  • Polygenic disorders
  • Environmental factors
55
Q

Single gene mutations

A

Refers to the cases when mutation in one particular gene will be enough to display a characteristic defect.

56
Q

Chromosomal anomalies (give an example)

A
  • In some cases, rather than single mutations, whole chromosomal rearrangements are responsible for a disease.
  • The most obvious examples are chromosomal trisomies, such as trisomy of chromosome 21, leading to Down syndrome.
57
Q

Polygenic disorders

A

Refers to cases where it is not just one gene affected, but several different genes simultaneously affected, what causes the disease.

58
Q

Environmental factors

A
  • Refers to the deleterious influence of the environment on a particular process.
  • These can be very diverse:
    • diet
    • infection,
    • toxic compounds.

MBD (23 decks)

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