Development of the Lungs Flashcards
Which structure is the point of transition from upper to lower respiratory tract?
Larynx
What 3 layers comprise the trilaminar embryonic disc?
Ectoderm, mesoderm, endoderm
What are the lung stages and what weeks do they occur?
- Embryonic –> week 4-5 2. Pseudoglandular –> week 5-17 3. Canalicular –> week 16-25 4. Saccular –> week 24-40 5. Alveolar –> late foetal to 8 years
When does the lung bud appear?
Day 22
Where does lung bud originate from? How does it grow?
Originates as an outgrowth from the ventral wall of the foregut - Grows ventrocaudally, anterior to the gut tube - Eventually divides to form 2 lung buds
What are tracheoesophageal ridges? What is there purpose?
- Longitudinal mesodermal folds that form as respiratory diverticulum grows - Separate the respiratory diverticulum from the foregut (separates trachea and oesophagus)
What is the respiratory diverticulum? When does it appear?
A ventral outgrowth of foregut endoderm Embryonic period –> day 22
What are tracheoesophageal fistualas (TOF) caused by?
Disruption of the formation of the tracheoesophageal ridges leading to abnormal connection between trachea (respiratory portion) and oesophagus
How common are TOF?
1 in 3000-4500 live births
What is TOF often associated with?
A spectrum of mesodermal defects –> VA(C)TER(L)
What are 90% of TOF associated with?
Oesophageal atresia
What is oesophageal atresia?
Failure of development of the proximal part
Proximal (upper) oesophagus ends blindly (sac)
Distal (lower) part of the oesophagus communicates with the trachea via a fistula
What are prenatal/postnatal complications of TOF?
Prenatally:
- Too much amniotic fluid as foetus cannot swallow amniotic fluid
Postnatally:
- Stomach contents can enter lungs (infection)
- Air can escape into stomach so adomen rapidly distends as stomach fills with air
- Infant coughs/chokes due to inability to swallow
What is an H-type tracheoesophageal fistula?
Fistula between trachea and oesophagus –> rarer (only 4% of cases)
What are consequences of H-type Tracheoesophageal fistula?
- Milk (from oesophagus) may be driven into respiratory system (infection)
- Stomach contents can enter respiratory system
What are the mesodermal defects often associated with TOF?
Vertebral defects (spinal bifida)
Anal atresia (anal canal not formed correctly)
Cardiac defects (most common)
Tracheo-oesophageal fistulas
Esophageal atresia
Renal abnormalities
Limb defects
How do lungs form during pseudoglandular stage?
Tubular branching –> during partioning of oesophagus and respiratory diverticulum, right and left lung buds form
Describe the order of formation of bronchi during the pseudoglandular stage
Week 5:
- Trachea divides into 2 1ary bronchi (right and left)
- 1ary bronchi divide into 2ary bronchi (3 on right, 2 on left)
Week 6:
- 2ary bronchi branch, resulting in formation of 3ary bronchial buds (bronchial tree)
- By end of 7th week, the 18 bronchopulmonary segments have been established (10 right, 8 left)
- Branching continues to form terminal bronchioles by week 16
What does developing lung resemble during pseudoglandular stage?
Branched, compound gland of endodermal air-conducting tubules