Respiratory System And Establishment Of The Body Cavities Flashcards
What organs does the endoderm form?
Lungs, digestive tract, liver, gall bladder, pancreas, thyroid gland & thymus.
When does human lung development begin?
Day 22.
Which type of cells form the epithelium of the respiratory system?
Endoderm of primitive foregut.
What does the splanchnic (lateral plate) mesoderm develop into?
Connective tissue, muscle, vasculature & bronchial cartilage.
What does the neural crest develop into?
Laryngeal cartilage.
What are the 4 stages of lung development?
- Formation of endoderm (flat disk).
- Folding of endoderm at cranial & caudal ends to make tube.
- Specification of endoderm into different organ derivatives.
- Branching of lungs & development of different cell types.
How does the primitive endodermal tube form into a blind ended tube?
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.
What is the function of the septum transversum?
To bring heart caudally as it develops.
Folding of embryo moves heart posteriorly.
Septum transversum becomes diaphragm as it folds.
What is ventral closure?
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.
Where is the ventral mesentery found in what is the part of?
Found in stomach & part of septum transversum.
What controls anterior-posterior patterning in the endoderm?
Differential expression HOX genes.
Expressed as nested domains along anterior-posterior axis in combinatorial code.
What does the dose of FGF signalling determine?
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.
What are the 5 periods of differentiation of lung development?
- Embryonic (26D-6W).
- Pseudoglandular (6-16W).
- Canalicular (16-28W).
- Saccular (28-36W).
- Alveolar (>36W).
What happens during the embryonic stages of lung development?
Induction to bronchopulmonary segment formation & generation of lung lobes.
Oligohydramnios can affect lung development at this stage.
What happens during the pseudoglandular stage of lung development?
Formation of terminal bronchioles:
- 14 generations of branching.
- Conducting airways & immature neural networks.
- Pre-acinar blood vessels.
What happens during the canalicular stage of lung development?
Formation of respiratory bronchioles:
- 1 round of branching.
- Vascularisation starts & blood vessels found close to lung epithelium.
- Epithelial cell differentiation & surfactant synthesis starts.
What is the cut-off week for premature birth?
26 week. There is sufficient alveoli to support respiration & surfactant synthesis has started.
What happens during the saccular stage of lung development?
Primitive alveoli formed:
- Extracellular matrix & neural matrix maturation.
What happens during the alveoli stage of lung development?
Mature alveolus:
- Expansion of gas exchange area (thinning of epithelium).
- Nerves and dense capillaries form.
- Formation of septae after birth.
What happens at/by birth?
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.
What does a mature alveolus contain?
Type I (gas exchange) & Type II (secrete surfactant) alveolar cells. Macrophages to phagocytose particulate matter.
What happens in oesophageal atresia & tranche oesophageal fistula?
Part of the oesophagus links to the trachea & the other (proximal) part of oesophagus is blind ending.
Dangerous in newborn & associated with polyhydramnios.
How does the trachea separate from the gut tube?
Via dorsal-ventral patterning. The trachea expresses Shh.
Which signalling molecules are required for lung growth and branching?
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.
