Flashcards in L24 – Development of the Respiratory System Deck (61):
What is stomodeum?
depression between the brain and the pericardium in an embryo
What divides the stomodeum into seperate division in the upper respiratory tract?
Palate divides stomodeum into Nasal and Oral cavities
What are the nasal and oral divisions of stomodeum precursors to?
Nasal = respiratory: nasal cavity, pharynx (throat), larynx
What is the lower respiratory tract responsible for in embryo's respiratory development?
Create pleural cavity
Extensive branching of airway within pleural cavity (e.g. bronchi, lungs)
Name of three germ layers at 3 weeks?
What are intraembryonic coelom and what germ layer are they formed from?
Form from lateral mesoderm
cavities between splanchnic mesoderm and somatic mesoderm layers > pleural, peritoneal...etc
What are the two germ layers for respiratory development?
When does Respiratory system begin to develop?
4 weeks old embryo
What proliferates at 4 weeks embryo to start respiratory system development?
At caudal end primordial pharyngeal arches, endoderm proliferates >
Form Respiratory Laryngotracheal Diverticulum
What structures does respiratory laryngotracheal diverticulum give rise to?
Lungs and Trachea
What folds in respiratory laryngotracheal diverticulum that seperates itself and esophagus?
Longitudinal Tracheoesophageal Ridge grows and fuses to form Tracheoesophageal Septum
What does the longitudinal tracheoesophageal septum seperate?
1. Dorsal: esophagus + oropharynx
2. Ventral: laryngotracheal tube/ respiratory bud
Which germ layer is tracheoesophageal ridge formed from?
endoderm surrounded by splanchnic mesoderm from lateral mesoderm on the outside
After week 5, what are the two main structures in embryonic resp. tract?
Esophagus, primordial laryngeal inlet
Laryngotracheal tube, Primary bronchial buds
What happens to laryngotracheal tube at week 4-5 embryo?
Elongate, forms trachea, lung buds divide into L/R primary bronchial buds
What is the median outgrowth from ventral part of pharynx?
What are the common congenital disorders to primordial respiratory system development?
All due to abnormal septation:
a) Tracheoesophageal fistulas (abnormal passage)
b) Atresias (blind-tube/blockage)
What is THE most common congenital disorder that affect 90% of lower respiratory tract development? What happens to upper and lower esophagus?
Type A- Tracheoesophageal fistula
Upper esophagus ends in blind pouch
Lower esophagus forms fistula with
trachea (tracheoesophageal fistula)
What is type B abnormal septation in embryonic resp.system?
Isolated esophageal atresia
Upper and lower esophagus ends sealed/ blind-ended
What is type C abnormal septation in embryonic resp. system?
H-type tracheoesophageal fistula
Both ends of esophagus communicate with trachea
What are the variant types of abnormal septation in embryonic resp. system?
Type D and E
What is the U-shaped intraembryonic / coelomic body cavity partitioned into?
2 pleural cavities
1 Pericardial cavities
1 Peritoneal cavities
How is the partitioning of intraembryonic coelom - pericardial and pleural cavities specifically - possible?
Pleuropericardial folds fuse and divides pleural and pericardial cavities
What separates the peritoneal cavity from pleural cavities?
Septum transversum & pleuroperitoneal membranes forms diaphragm > close off pericardioperitoneal canals > separate peritoneal cavity from the 2 pleural cavities
What is a common congenital problem in the septation of peritoneal and pleural cavities?
Failure of Septum Transversum and Pleuroperitoneal membranes to grow across intraembryonic coelem/ pericardioperitoneal canal
= congenital diaphragmatic hernia
Which layer of the respiratory laryngotracheal diverticulum forms the pleura?
Surrounding splanchnic mesoderm
What is the purpose of the formation of diaphragm by Septum transversum and Pleuroperitoneal membrane?
Separate pleural and peritoneal cavities
Pleural cavity has to be air-tight
Contain lung buds expansion towards diaphragm
Embryonic diaphragm is divided into anterior and posterior part. Origin of each part? What forms peripheral part of diaphragm?
Anterior = Septum transversum
Posterior = Pleuroperitoneal membrane
Peripheral = muscular ingrowth from body wall
What happens to lung buds at week 5-6?
Lung buds expands and grow downwards towards pericardioperitoneal / pleural canal
What are the two embryonic origins of the two lung pleura?
Parietal pleura: from somatic mesoderm
Visceral pleura: from splanchnic mesoderm
When does pleuralpericardial folding occur in embryonic resp. system?
Week 5 - 6
What foldings/ septations have occurred by week 5?
Tracheoesophageal fold > Pleuropericardial folds > Septum transversum & Pleuroperitoneal membrane
What does the mediatinum do? When is it developed?
Septation of viscera and connective tissue between pleural cavities
By Week 7-8
When do the two parts of embryonic diaphragm fuse?
When does pleuroperitioneal FOLDS (not membrane) appear?
grows ventrally from dorsal body wall
The laryngotracheal tube elongates and forms Trachea and bronchial buds. What are the subsequent bud divisions?
Primary (main) bronchi divides to give secondary bronchial buds (= future lung lobes; asymmetrical: 左二右三)
What follows secondary bronchial buds in developing embryonic lungs?
branches into tertiary (segmental) bronchial buds (= future bronchopulmonary segments; 左八右十)
What follows tertiary (segmental) bronchial buds in developing embryonic lungs?
Tertiary (segmental) bronchi continue to divide for 23-30+ generations into bronchopulmonary segments, terminates at alveoli
How do the layers of laryngotracheal tube differentiate into different structures?
Endoderm lining > typical respiratory epithelium and glands
Mesoderm > 2 pleura
How can bronchial bud division give rise to accessory lobes (abnormal) (e.g. double right-handedness)?
If the divisions are unequal up to 18th division
What proportion of number of alveoli are present at birth?
The remaining develops postnatal
The Left lung is divided into Upper and Lower lobes. How is the Left Upper Lobe further divided (not by oblique fissure)?
Left Upper lobe > Superior division and Lingular division
Do the maturation phases of embryonic lung overlap? Why?
Caudal and Ventral region of lungs mature at different pace
What 4 stages of lung maturation in embryo and post natal? What are the timelines? (PCTA)
Pseudoglandular period (Week 5-17)
Canalicular period (week 16-25)
Terminal Sac period (Week 24- birth)
Alveolar period (Week 32 to childhood)
What is alveoli lined by in first stage of embryonic lung maturation? Are lungs functional then?
Pseudoglandular period (week 5-17)
Alveoli lined by tall columnar epiuthelium
No gas exchange
What occurs in the second maturation phase of lungs ?
Canalicular period (Week 16-25)
Alveolar ducts lines by cuboidal epithelium > separate respiratory bronchiolus from terminal bronchiolus
Why is there no gas exchange in the second stage of embryonic lung maturation?
Blood capillaries still far away from the cuboidal epithelium of respiratory bronchiolus in Canalucular period
What occurs in 3rd stage of lung maturation?
Terminal Sac period, week 24- birth
Cuboidal epithelium becomes squamous at terminal sacs, Blood and lymph vessels move towards terminal sacs and become intimately related
In which stage is gas exchange possible?
Terminal Sac Period , 3rd stage, week 24-birth
What occurs during the fourth stage of embryonic lung maturation?
Alveolar period (32nd week until 8-10 years old)
Rapid growth and maturation
Number of respiratory bronchioles and primitive alveoli increases
What epithelium in embryonic alveoli can you expect at week 26?
Transition from cuboidal to squamous
between 2nd and 3rd stage of maturation
What two cells in embryonic alveoli can you expect at week 32?
Type I and II pneumocytes/ alveolar cells
At which week do terminal bronchioles form?
How does fetal breathing change neonatal and postnatal?
Neonatal = aspirates amniotic fluid into lungs
Postnatal = fluid clearance and replace by air
How is it that postnatal lungs can clear fluid aspired before birth?
1. Expulsion by pressure on thorax during delivery
2. Entering into lung capillaries
3. Passing into lymph vessels
What natural chemical is critical to prevent lung collapse at birth?
Surfactant made by mature type II pneumocytes can reduce intra-alveoli surface tension
Apart from Tracheoesophageal fistula, What are the two common congenital malformations related to resp. tract formation?
Respiratory distress syndrome (RDS)/ Hyaline membrane hernia
Congenital diaphragmatic hernia
What is fetal RDS caused by?
Insufficient surfactant production > hyaline membrane disease
Deficiency or prolonged asphyxia > lungs to under-inflate > collapse alveoli > Fatal to premature infants
How to alleviate RDS in premature infant?
Inject hormone to induce surfactant release or Inject artificial surfactant
What is congenital diaphragmatic hernia caused by? What is the consequence in organ arrangement ?
Failure of plueroperitoneal membrane to grow across pericardioperitoneal
canals/ intraembryonic coelom
Large part of (usually left) diaphragm missing
Intestinal loops, stomach, spleen, part of liver enter thoracic cavity