1.1.2 Development of the Respiratory System Flashcards
Respiratory diverticulum or lung bud is an outgrowth of what?
The endodermal tube
Epithelium of the respiratory system is derived from what germ layer?
Endoderm
Cartilaginous, muscular and connective tissue components of the trachea and lung are derived from?
Splanchnic mesoderm
What does the traschoesophageal septum form from?
The tracheoesophageal ridges
Tracheoesophageal ridges fuse together to form the tracheoesophageal septum. It is the tracheoseophageal septum that is responsible for separating the tracheal primordium from the esophageal primordium.
Pseudostratified ciliated with goblet cells, endoderm
How many lung buds does the right lung have? Left?
3 for the right
2 for the left
What are the pericardioperitoneal canals?
The narrow spaces that are gradually filled by the expanding lung buds.
they connect the primordial pericardia with the lower peritenal cavities - these are closed by septum transversum = diaphram
What separates the pericardioperitoneal canals from the peritoneal and pericardial cavities?
pleuroperitoneal and pleuropericardial folds
What germ layer forms the visceral and parietal pleura?
Mesoderm
Once the pericardioperitoneal canals separate from the pericardial and peritoneal cavities what occurs?
The lungs will begin to expand into the pleural cavities
During the 5th week, pleuropericardial folds grow out from the lateral body wall toward the midline. What are the next steps following this?
They fuse with each other and with mesoderm associated with the esophagus. Simultaneously, the roots of these folds migrate ventrally so that they ultimately originate from the ventral body wall.
What is the role of the pleuropericardial folds?
The pleuropericardial folds with their associated serous membrane form the pericardial sac and transform the primitive pericardial cavity into a definitive pericardial cavity and right and left pleural cavities.
Explain the relationship between the septum transversum and the pericardioperitoneal canals.
In the future thoracic region, the septum transversum forms a ventral partition beneath the paired pericardioperitoneal canals (arrows), which interconnect the primitive pericardial cavity cranially and peritoneal cavities caudally.
Explain how the separation of the abdominal and thoracic cavities occurs. (Think diaphragm formation).
Closure of the pericardioperitoneal canals. Between weeks 5 and 7, a pair of horizontal pleuroperitoneal membranes grow from the posterior body wall to meet the septum transversum (arrows) A, thus closing the pericardioperitoneal canals. These membranes form the posterior portions of the diaphragm and completely seal off the pleural cavities from the peritoneal cavity. Arrows in B indicate invasion of the developing diaphram by muscle fibers from the adjacent body wall.
What components make up the diaphragm?
The definitive diaphragm is a composite structure including elements of the septum transversum, pleuroperitoneal membranes, and esophageal mesenchyme, as well as a rim of body wall mesoderm.
What is a diaphragmatic hernia?
A hole in the diaphragm leads to parts of the intestine being in the chest cavity. This can cause pulmonary hypoplasia and pulmonary insufficieny.
What is correct about the previously described congenital anomaly?
- it is found on the right side
- frequently associated with hyperplastic lungs
- best diagnosed on physical exam of the mother
- frequently asymptomatic at birth
- frequently presents with a scaphoid abdomen
- frequently presents with a scaphoid abdomen
How do patients with diaphragmatic hernia respond to bag-mask ventilation?
They tend to get worse
Where do 90% of diaphragmatic hernias occur?
They occur on the left side
Why can bag-mask ventilation make neonates with diaphragmatic hernia worse?
This causes the stomach and bowel to fill with gas which will further compromise respiration and cardiac action
Why are abdomens considered scaphoid in a child with a diaphragmatic hernia?
The abdomen is displaced into the chest.
The pleuropericardial folds will divide what?
The thoracic portion of the body cavity into the pleural and pericardial cavities
What is the terminal sac period and when does it occur?
Terminal sac period is phase in which the blood-air-barrier is formed with surfactant, type I pneumocyte and its basal lamina, and a capillary endothelial cell and its basal lamina.
26 weeks until birth
What is the pseudoglandular period of lung maturation?
Branching has continued to form terminal bronchioles, but not alveoli are present
5-16 weeks
What is the canalicular period of lung maturation?
Each terminal bronchiole divides into 2 or more respiratory bronchioles which in turn divide into 3-6 alveolar ducts
16-26 weeks
What is the alveolar period?
Mature alveoli have well-developed epithelial endothelial contacts
8 months to childhood
During the canalicular period what cells line the respiratory bronchiole? How does this change during the terminal sac period?
Canalicular Period: Cuboidal cells line the respiratory bronchiole
Terminal Sac Period: Cuboidal cells become very thin and are intimately associated with the endothelium of blood and lymph capillaries or form terminal sacs (primitive alveoli).
What period is this an image of?
Pseudoglandual period
Note the glandular appearance of the organ
What period of lung maturation is this an image of? Can you name what all the arrows are?
Terminal Sac Period
Why is the terminal sac period important?
The terminal sac period is the phase of lung development in which the blood-air-barrier is established with type I pneumocytes and capillary endothelial cells, their basal laminae, and a thin layer of surfactant.
What drives the development of endoderm?
Mesenchyme
What is the role of Tbx5 and RA in branching morphogenesis?
TBx5 is a T-box transcription factor; RA is the abbreviation for retinoic acid, and signaling by these lead to the induction of mesenchyme to secrete FGF10.
FGF10 binds to what?
FGFR2
How do FGF, Shh and BMP4 cause branching?
What is the role of Sprouty and TGF-B in branching?
Sprouty restricts branching to the tip and TGF-B stimulates ECM deposition and inhibits cell proliferation
What is oligohydramnios?
Amniotic Fluid index - a measure of total amniotic fluid. Oligohydramnios is an AFI < 5cm
Less urine output = less fluid
What is polyhydramnios?
AFI > 24cm
Less swallowing = more fluid
What are the symptoms of a tracheoesophageal fistulae in a newborn?
Copious salivation associated with choking, coughing, vomiting and cyanosis coincident with the onset of feeding.
Infants with TEF are at increased risk for defects in what?
The VACTERL defects
Vertebral, Anal atresia, cardiac defects, renal and limb defects
What is a promixal esophageal atresia and distal TEF? Is this the most common?
Yes it is the most common
What is hypertrophic pyloric stenosis?
Hypertrophic pyloric stenosis is a form of gastric outlet obstruction that results from congenital thickening of the muscle of the pylorus. The result is a narrowing of the lumen of the pylorus and therefore, the outlet to the duodenum.
What is an important symptom associated with hypertrophic pyloric stenosis?
Non-bilious projectile vomiting following feeding
What is the most common cause of oligohydramnios?
Early leaking of the amniotic fluid due to premature rupture of membranes that surround fetus. This can restrict fetal breathing which is vitally important for normal lung development
What is the second most common cause for oligohydramnios?
Fetal renal anomalies. Amniotic fluid is produced by the amniotic membranes and the fetal kidneys. Abnormalities in the fetal kidneys can cause too little amniotic fluid to be produced.
Oligohydramnios is strongly associated with what?
Limb malformations and severe lung immarturity
What are these images of?
Hypoplasia of the lung due to oligohydramnios
What is congential lobar emphysema?
Collapsed bronchi occur because of congenitally weakened or absent cartilage in the wall of the bronchi. Sometimes more lobes of the lung are over-distended with air because air can be inspired through collapsed bronchi, but cannot be expired.
What is aeration at birth?
Replacement of liquid with air in the lungs
What are the complications of TEFs?
Polyhydramnios, pneumonitis, and pneumonia
What is neonatal respiratory distress syndrome?
Surfactant deficiency in neonates. Can be caused by mothers with diabetes. This deficiency can cause the lungs to collapse with each successive breathe.
What is the role of the septum transversum?
It grows towards the pleuroperitoneal fold to help form the diaphragm
In a child with diaphragmatic hernia, what is often the fatal complication associated with it?
Severe pulmonary hypoplasia and pulmonary insufficiency may often be fatal.
