Embryo respiratory system Flashcards
What is the septum transversum?
Part of mesoderm above buccopharyngeal membrane that develops into mesenchymal cell mass below the heart, forming the majority of the diaphragm and contributing to mesenchyme of liver, etc.
2 general EARLY steps of lung development
- Position lung primordium
2. Primary lung bud formation
General LATE step of lung development
Bronchial branching and cellular differentiation
Txn factor that determines location of initial lung development
Linked to increase of what molecule produced by mesoderm
TBX4
Retinoic acid
When does lung development begin?
From what structure do the lungs/trachea form from?
Week 4
Off of the foregut - to become the esophagus
Very first step in tracheal development
What does the original opening become?
Bulging of laryngeotracheal (respiratory) diverticulum from the endoderm (foregut/esophagus)
The laryngeal orifice
What forms just below the laryngeal orifice (split off of the trachea from the esophagus)?
Tracheoesophageal septum
What tissue layer is directly covering the esophagus and start of the trachea?
What is covering that?
Endoderm
Splanchnic mesoderm
SO, the opening of the trachea and start of it is called what again?
Laryngeotracheal diverticulum
Most common malformation during lung/esophageal development
What is it?
Tracheoesophageal fistula
Improper formation of TE septum leads to an esophagus dead end, and the esophagus continuing down from off the trachea
What’s the name of an esophagus dead?
What’s the name of the esophagus that branches down from off the trachea (comes w/ a dead end higher up)?
Root cause?
Esophageal atresia
TE fistula
Malformation of TE septum
The esophageal atresia (dead end) fills with air and causes what?
An anterior displacement of the trachea
How is esophageal atresia diagnosed/presented?
Infant w/ excessive salivation, frequently w/ choking, coughing, sneezing
How is swallowing vs. movement of food to stomach affected in these cases?
Swallowing = normal
Immediate coughing as fluid returns up through nose and mouth (goes into trachea, causing the cough)
W/ esophageal atresia and TE fistula, how might the skin of the infant present?
Why?
Cyanotic (blue)
Overflow of fluid into trachea and lungs prevents breathing
How to surgically fix TE fistula?
Cut distal esophagus from trachea, fix the hole, then suture the esophagus to the proximal (upper) atresia portion to make a normal esophagus
What is a laryngeal cleft?
Due to what?
Common when?
Space between esophageal opening and tracheal opening, causing food to pass into airways
Difficulty w/ cartilage separating trachea from esophagus
Associated w/ TE fistula, etc.
Other tracheal structural abnormality associated w/ TE fistula, etc.?
What is it?
Treatments?
Tracheal stenosis
Abnormal narrowing
Balloon dilation and tracheal stents
When do the primary bronchi begin to form?
Start as what?
Week 5
Bronchial buds
How is bronchial branching developed?
Sequential budding of primary, secondary, tertiary bronchii, bronchioles, etc.
Name of lining around lungs themselves
Comes from what layer?
Name of lining around pulmonary cavities
Comes from what layer?
Visceral pleura - splachnic mesoderm
Parietal pleura - somatic mesoderm
When do the tertiary bronchial buds form?
Week 6
The splanchnic mesoderm differentiates into the ___, ___, and ___ of the lungs
Smooth muscle
Nerves
Blood vessels
The ___ regulates the pattern of branching of lung endoderm (inner lining)
Surrounding mesenchyme
Bronchioles and alveoli are designed to maximize ___ while minimizing ___
Surface area for gas exchange
Resistance to air flow
According to what equation, increased alveolar surface area (more branches) should ___ resistance due to decreased diameter
SO, an airway segment is never more than ___ its diameter
R = L/r4
Increase
3x
5 main stages of lung development (w/ time periods)
At what stage is a fetus technically viable for birth?
Embryonic - weeks 4-7 Glandular - weeks 8-16 Canalicular - weeks 17-26 Terminal sac - weeks 26-birth Postnatal (alveolar)
Canalicular
What happens in the embryonic stage of lung development?
Weeks?
Form diverticulum –> form major bronchopulmonary segments
Lungs grow into pleural cavities
4-7
What happens in the glandular stage of lung development?
Weeks?
Duct systems w/in BP segments form
8-16
Induction of vasculogenesis of pulmonary veins is mediated by what txn factor?
Expressed where?
When?
VEGF
Epithelium of terminal buds of fetal lung
Late glandular stage
What happens in the canalicular stage of lung development?
Weeks?
Respiratory bronchioles, terminal sacs form
Increased vascularization, capillaries in walls
17-26
2 main cell types in alveoli differentiate from what common cell type?
Epithelial lining of alveoli
Two cell types w/in alveoli (w/ functions)
Type 1 pneumocyte - blood-air barrier
Type 2 pneumocyte - secrete surfactant to reduce surface tension and expand alveoli w/ the liquid
Which surfactant type forms first?
Which types come later?
Surfactant C
A and B
Why is lung surfactant so important in development?
Allows easy expansion of alveoli while reducing surface tension
What % of alveoli form before birth?
Mechanism of alveolar growth/division?
10%
Septation of pre-existing alveoli
Which alveolar cell type develops first?
During what stage?
When does the other cell type form?
Type 2
Glandular
Canalicular
What is a supernumary bronchus?
Main type?
Symptoms?
Abnormal division, leading to extra primary/secondary bronchioles
Main = bronchus to right upper lobe is directly from trachea, NOT from right primary bronchus
NONE (usually)
An additional respiratory bud from the foregut can cause the formation of what irregularity?
Generally via misexpression of what txn factor?
Ectopic lung lobe
FGF10
What is infant respiratory distress syndrome (IRDS)?
Can cause what?
Labored breathing due to lack of surfactant
Atelectasis - incomplete expansion or collapse of parts or whole lung
If an alveolus collapses, what happens around it?
Why is this bad?
Other alveolus gets bigger
Bigger radius = worse surface area for gas exchange
If alveoli are collapsed, what else would be seen?
Dilated bronchioles
W/in collapsed alveolar spaces, what accumulates?
Debris, edema, RBCs
What would you see in alveolar ducts near a collapsed alveolus?
Fibrin-rich hyaline membrane from damaged alveolar cells
Hyaline membrane disease
X-ray appearance?
Alveoli filled w/ debris
“Ground glass” appearance in chest x-ray
Congenital neonatal
emphysema
Developmental cause?
Collapsed bronchi cause over-distention of one or more lobes w/ air caught inside
Bronchial cartilage doesn’t develop
Congenital bronchial cysts
Increased incidence of what?
Radiograph appearance?
Destruction and dilation of large airways, filled w/ mucous pockets
Infection
Honeycomb appearance
Pulmonary agenesis
Developmental cause?
Complete lack of lung
Bronchial bud doesn’t develop
Pulmonary hypoplasia
Cause?
Secondary result?
External structural result?
Poorly developed bronchial tree due to insufficient amniotic fluid (oligohydramnios)
Renal agenesis, causing lack of fluid to help develop renal system
Limb defects b/c not enough room in amniotic sac to move limbs around
Potter syndrome
Pulmonary hypoplasia and kidney failure due to lack of amniotic fluid
Polyhydramnios
Cause?
High volume of amniotic fluid
Infant can’t swallow fluid
The intraembryonic coelom (initial body cavity) is first partitioned into the thoracic and abdominal portions via what?
Formation of the septum transversum and pleuroperitoneal membranes, forming the diaphragm
The thoracic cavity is further divided into pericardial and pleural cavities via what?
What nerves run through this structure?
Pleuropericardial membranes
Phrenic and vagus
When does the diaphragm become innervated by the phrenic nerve?
When does it move down to L1?
Week 4
Week 8
Congenital diaphragmatic hernia
Caused by what?
Most commonly where?
Hole in diaphragm, causing leaking of abdominal viscera into the thoracic cavity
Failure of pleuroperitoneal membranes to fuse
Left posterolateral side
Clinical signs of a congenital diaphragmatic hernia
Unusually flat abdomen, breathlessness and cyanosis (compressed lungs)
Common surgical tx for diaphragmatic hernia
Tie of trachea so fluid builds up in lungs and causes herniated organs to be pushed out
Then untie trachea, let baby breathe, and cut umbilical cord
