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Developmental Basis Of Birth Defects > Respiratory System And Establishment Of The Body Cavities > Flashcards

Respiratory System And Establishment Of The Body Cavities Flashcards

1
Q

What organs does the endoderm form?

A

Lungs, digestive tract, liver, gall bladder, pancreas, thyroid gland & thymus.

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2
Q

When does human lung development begin?

A

Day 22.

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3
Q

Which type of cells form the epithelium of the respiratory system?

A

Endoderm of primitive foregut.

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4
Q

What does the splanchnic (lateral plate) mesoderm develop into?

A

Connective tissue, muscle, vasculature & bronchial cartilage.

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5
Q

What does the neural crest develop into?

A

Laryngeal cartilage.

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6
Q

What are the 4 stages of lung development?

A
  1. Formation of endoderm (flat disk).
  2. Folding of endoderm at cranial & caudal ends to make tube.
  3. Specification of endoderm into different organ derivatives.
  4. Branching of lungs & development of different cell types.
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7
Q

How does the primitive endodermal tube form into a blind ended tube?

A

Primitive gut is formed by differential growth and by lateral
and craniocaudal folding = ‘making a bed’.
Transform endoderm from flat disk & into foregut, midgut & hindgut.
Yolk sac which grows very little, remains through the vitelline duct.
Allantois (slender diverticulum) is formed by hindgut. This is incorporated into umbilical cord at day 26.

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8
Q

What is the function of the septum transversum?

A

To bring heart caudally as it develops.
Folding of embryo moves heart posteriorly.
Septum transversum becomes diaphragm as it folds.

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9
Q

What is ventral closure?

A

Splanchnic mesoderm fuses above & below gut tube, forming dorsal and ventral mesentery.
Dorsal mesentery remains, while epidermis and mesoderm close around gut to form the ventral body wall.

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10
Q

Where is the ventral mesentery found in what is the part of?

A

Found in stomach & part of septum transversum.

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11
Q

What controls anterior-posterior patterning in the endoderm?

A

Differential expression HOX genes.

Expressed as nested domains along anterior-posterior axis in combinatorial code.

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12
Q

What does the dose of FGF signalling determine?

A

Which organs develop in the anterior endoderm.
Anterior FGF forms thyroid gland & posterior FGF forms pancreas.
Heart expresses FGF2 and FGF1.

FGF signalling also required for lung induction & later lung development.

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13
Q

What are the 5 periods of differentiation of lung development?

A
  1. Embryonic (26D-6W).
  2. Pseudoglandular (6-16W).
  3. Canalicular (16-28W).
  4. Saccular (28-36W).
  5. Alveolar (>36W).
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14
Q

What happens during the embryonic stages of lung development?

A

Induction to bronchopulmonary segment formation & generation of lung lobes.
Oligohydramnios can affect lung development at this stage.

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15
Q

What happens during the pseudoglandular stage of lung development?

A

Formation of terminal bronchioles:

  • 14 generations of branching.
  • Conducting airways & immature neural networks.
  • Pre-acinar blood vessels.
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16
Q

What happens during the canalicular stage of lung development?

A

Formation of respiratory bronchioles:

  • 1 round of branching.
  • Vascularisation starts & blood vessels found close to lung epithelium.
  • Epithelial cell differentiation & surfactant synthesis starts.
17
Q

What is the cut-off week for premature birth?

A

26 week. There is sufficient alveoli to support respiration & surfactant synthesis has started.

18
Q

What happens during the saccular stage of lung development?

A

Primitive alveoli formed:

- Extracellular matrix & neural matrix maturation.

19
Q

What happens during the alveoli stage of lung development?

A

Mature alveolus:

  • Expansion of gas exchange area (thinning of epithelium).
  • Nerves and dense capillaries form.
  • Formation of septae after birth.
20
Q

What happens at/by birth?

A

Fluid must be removed by, absorption in lungs, pressure on chest during birth & surfactant synthesis.
Is an increase in surface area due to thinning of epithelial layer (type I cells, squamous), followed by formation of septae after birth.
Must produce protective lining for lungs.

21
Q

What does a mature alveolus contain?

A 
Type I (gas exchange) & Type II (secrete surfactant) alveolar cells.
Macrophages to phagocytose particulate matter.
22
Q

What happens in oesophageal atresia & tranche oesophageal fistula?

A

Part of the oesophagus links to the trachea & the other (proximal) part of oesophagus is blind ending.
Dangerous in newborn & associated with polyhydramnios.

23
Q

How does the trachea separate from the gut tube?

A

Via dorsal-ventral patterning. The trachea expresses Shh.

24
Q

Which signalling molecules are required for lung growth and branching?

A

For proximal-distal bud induction, the distal mesenchyme has FGF10 that acts on FGFR2b.
For mesenchymal survival, proliferation & differentiation, retinoic acid acts on FGF9 that acts on distal mesenchymal, where Shh also acts on distal mesenchymal.

25
Q

What are the 4 tissue origins of the diaphragm?

A
  1. Septum transversum.
  2. Body wall (somitic) mesoderm.
  3. Pleuroperitoneal membranes.
  4. Oesophageal (splanchnic) mesoderm.
26
Q

What is congenital diaphragmatic hernia?

A

Posterolateral hernia into the thorax of abdominal content.

More common on the left side. FOG2 transcription factor may be involved.

27
Q

What is primary cilia dyskinesia?

A

Cilia dysfunction leading to recurrent lung infections. Due to:

  • Defect in “motile” cilia.
  • Autosomal dominant leading to 50% of cases of Kartagener syndrome (KS). KS defect in dynein rods (mutations in dynein proteins) that make cilia motile.
28
Q

What are the 3 types of cilia?

A
  1. Primary or sensory: 9 + 0, single cilia, non-motile chemo/mechansors & WNT PCP & Hh signalling. E.g. Retina.
  2. Motile or epithelial: 9 + 2, Many, beat in orchestrated fashion & fluid movement. E.g. Trachea.
  3. Nodal: 9 + 0, single cilia, propeller-like movement, establishment L-R axis (via Lefty & Pitx2) E.g. Node in gastrulating embryo.
29
Q

What is left isomerism?

A

Linked with maternal diabetes. 2 long narrow cardiac atrial appendages. Both lungs bilobed & polysplenia.

30
Q

What is right isomerism?

A

Both cardiac atrial appendages are pyramidal in shape. Both lungs are trilobed & asplenia.

31
Q

What happens to nodal flow in normal, immotile & dysfunctional cilia?

A

Normal: Fast nodal flow.
Immotile: No nodal flow.
Dysfunctional: Slow nodal flow.

32
Q

What happens in retinitis pigmentosa?

A

Photoreceptors have modified cilia. Leads to failure to remove rhodosphins, which accumulates & cell dies.

Developmental Basis Of Birth Defects (5 decks)

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