Respiratory embryology Flashcards
Where does the upper respiratory tract run from?
The nasal cavities to the oropharynx
Where does the lower respiratory tract run from?
The larynx to the alveoli
Where does the conducting portion of the respiratory tract run from?
The nasal cavities to the terminal bronchioles
Where does the respiratory portion of the respiratory tract run from?
The respiratory bronchioles to the alveoli
What germ layer is the respiratory tract derived from?
Respiratory epithelium from the endoderm
The supporting structures ie. musculature, cartilage and vasculature all derived from the mesoderm
Where does the respiratory diverticulum/lung bud appear from?
The ventral wall of the foregut
On what day does the lung bud appear?
Day 22
What separates the respiratory diverticulum from the foregut?
The tracheoesophageal ridges
In how many cases are tracheosophageal fistulas associated with oesophageal atresia?
85-90%
What are the signs of tracheoosophageal fistula with oesophageal atresia in the newborn?
Distended abdomen (swallows air)
Regurgitation of milk
lung infection as stomach contents can enter the lungs
What is a H type tracheosophageal fistula?
No oesophageal atresia but a connection between oesophagus and trachea
Occurs is approximately 4 % of cases
Similar symptoms to that with oesophageal atresia but can still swallow
What other congenital abnormality are tracheoesophageal fistulas commonly associated with?
Cardiac defects
What are the VACTERL commonly associated congenital abnormalities?
V = vertebral defects A = anal atresia C = cardiac defects T = TOFs E = Esophageal atresia R = Renal abnormalities L = limb defects
How many secondary bronchi do you have on the right and left and during which week do they form?
Week 5
3 on right
2 on left
One to each lobe
How many tertiary bronchi do you have on the right and left and in which week do they develop?
Week 6
10 on right
8 on left
Each supply a bronchopulmonary segment
In which weeks do the terminal bronchioles, respiratory bronchioles and alveoli develop?
Terminal bronchioles = by Week 16
Respiratory bronchioles = by Week 26
First alveoli develop in week 36
What is the branching of the respiratory tract during development regulated by?
Interaction between the respiratory epithelium (Derived from the foregut) with the overlying visceral mesoderm
What part of the lungs is derived from the visceral mesoderm?
Cartilage, smooth muscle, connective tissues and capillaries
What forms the visceral and parietal pleura of the lungs?
Visceral pleura = visceral mesoderm
Parietal pleura = parietal mesoderm
What is pulmonary agenesis and what are the 2 types?
Occurs when lung bud fails to split
Complete absence of bronchi and vasculature
Can be unilateral or bilateral
Bilateral agenesis is incompatible with life
What is pulmonary hypoplasia and how severe is it?
All components of the lung are present but are incompletely developed
Severity of hypoplasia determines the degree of compromise
What other congenital defect is pulmonary hypoplasia commonly associated with?
Congenital diaphragmatic hernia
What is branching morphogenesis and how does this affect function?
Supernumerary lobes or segments
Little functional significance
What 4 sections can maturation of the lungs be divided into?
1) Pseudoglandular
2) Canalicular
3) Terminal Sac
4) Alveolar
What weeks is the pseudoglandular period from, how far does the respiratory system develop in this period and is respiration possible?
5-17 weeks
Terminal bronchioles have formed
Respiration not possible - fetus could not survive
What is the canalicular period from, how has the structure of the respiratory tract developed and is respiration possible?
16-25 weeks
Terminal bronchioles give rise to respiratory bronchioles which give rise to alveolar ducts, mesoderm also becomes highly vascularised
Respiration is possible towards the end of this period but low chance of survival
When is the terminal sac period from, what structural changes occur to the lungs?
17 weeks to birth
Further terminal sacs (primitive alveoli develop) Epithelium thins and comes into contact with capillaries, blood air barrier forms
respiratory epithelium divides into type 1 and type 2 pneumocytes which produce surfactant
Can a fetus born prematurely survive?
Yes (24 weeks) if given intensive care but may suffer from respiratory distress syndrome
When is the alveolar period from, what kind of development happens during this period?
36 weeks - 8 years
Development mainly due to increase in the number of respiratory bronchioles and and alveoli
What percentage of mature alveoli develop after birth?
95%
When does breathing movements begin and why?
Starts in utero and serves to remove amniotic fluid and also kick starts muscles of respiration into action
What happens to the fluid the lungs and what does the babies first breath cause?
Any remaining fluid in the lungs is reabsorbed by the capillaries
The first breath causes circulatory changes
What is usually the prime factor in a babies survival if born prematurely?
The state of development of the lungs - the presence of the respiratory portion of the system but also alveoli
Why does respiratory distress syndrome occur?
Absence of surfactant
What happens in respiratory distress syndrome?
Laboured breathing as it threatens the infant with asphyxiation
Increased breathing rate
What is needed to support the babies breathing in respiratory distress syndrome but what can this cause?
Mechanical ventilation
Damage to the alveolar lining , fluid and serum proteins leak into the alveolus
Continued injury may lead to detachment of the alveolar lining
What is bronchopulmonary dysplasia and what can it be caused by?
Abnormal formation of part of the lung
Can be caused by chronic injury to the lungs in preterm infants from mechanical ventilation
What is the treatment to prevent respiratory distress syndrome?
1) Glucocorticoid treatment accelerates fetal development and surfactant production
2) Surfactant therapy - natural or artificial
What must be present in artificial surfactant for it to be optimally effective?
Surfactant A and B proteins
What is surfactant B protein deficiency caused by and what is the prognosis?
Genetic condition - autosomal recessive
Fatal disease even with surfactant replacement therapy
