Embryology of respiratory system Flashcards
When does the respiratory diverticulum form?
week 4, appears day 22
What does the tracheo-esophageal ridge separate?
the esophagus, and trachea/lung bud
What is the origin of the epithelium of the lining of the larynx, trachea, bronchi, and lungs?
Endodermal (foregut)
What is the origin of the cartilaginous, muscular, and connective tissue components of the trachea, bronchi and lungs? What is the tracheal cartilage derived froms?
1) Splanchnic mesoderm surrounding the foregut
2) tracheal cartilages are derived form neural crest cells
What is a trachea-esophageal fistula?
Abnormal communications between the trachea and esophagus due to incomplete division of foregut
What is a complication of trachea-esophageal fistula?
Polyhydromnios, since amniontic fluid does not pass down into the stomach and intestine
Tracheo-esophageal fistula with Esophageal atresia
Upper esophagus ends abruptly; lower esophagus forms fistula with trachea. Abdomen distension from air in stomach. Milk may be driven into respiratory system.
What is H-type fistula?
Fistula between trachea and esophagus. Milk may be driven into resp system
What anomalies or defects are associated with TEF?
V - vertebral A - Anal atresia C - Cardiac T - tracheo esophageal fistulas E - Esophageal atresea R - renal L - limb
When does formations of main and secondary bronchi usually happen?
week 5
Which main bronchus do foreign objects are likely to get lodge?
Right main bronchus because it descends more vertical and has a larger lumen
How many tertiary or segmental bronchi form in the right and left lungs?
right - 10
left - 8-10 (Nunn’s notes has the combined form apico-posterior, and antero-medial basal)
What regulates the bronchi branching?
-regulated by epithelial-mesenchymal interactions between the endoderm of the lung bud and the splanchic mesoderm that surrounds them
What forms the pleura?
Splanchnic mesoderm form visceral pleura
Somatic mesoderm form parietal pleura
What are the 4 periods of lung maturation? What are the relative time frames?
1) Pseudoglandular - 5-17 wks
2) Canalicular - 16 - 25 (28) wks
3) Terminal Sac - 24-birth
4) Alveolar -Birth to 8 years
What occurs in pseudoglandular period?
-terminal bronchioles form. Respiration not possible.
What occurs in canalicular period?
- Respiratory bronchioles forms, which give rise to alveolar ducts. Mesodermal tissue becomes highly vascularized. Respiration is possible towards the end as some terminal sacs (alveoli) are formed, however may cause resp distress syndrome.
What occurs in terminal sac period?
- further terminal sacs develop. Capillaries come into contact with epithelium. Blood-air barrier formed. Epithelium differentiates to pneumocyte type 1 (where gas exchange happen) and type II (secrete surfactant). Fetus born prematurely (24 wks) can survive but may suffer resp distress syndrome.
What is the function of surfactant?
-forms a film over internal walls of terminal sacs, which decreases surface tension thus facilitating inflation and prevent collapse of alveoli during expiration
What occurs in the alveolar period?
- increase number of resp bronchioles and alveoli. 95% of mature alveoli do not develop until after birth
What is atelectasis?
collapse of alveoli during expiration
What happens to lung fluid during birth?
1) absorbed by blood and lymph capillaries
2) expelled via trachea and bronchi during delivery
What causes bronchopulmonary dysplasia?
dysplasia or abnormal formation can be caused by chronic lung injury in preterm infants
What is respiratory distress syndrome (RDS)?
- labored, increase rate of breathing
- may need ventilation
- fluid/serum protein leak into alveolus
- risk for asphyxiaton
- may cause alveolar damage, or detachment (hyaline membrane disease)
- chronic injury may cause bronchopulmonary dysplasia
Treatment for respiratory distress syndrome in premature neonates.
- Glucocorticoid treatment: to accelerate fetal lung development and surfactant production
- artificial surfactant therapy, with supplementary proteins found in surfactant, such as proteins A and B.
what is surfactant B deficiency disease?
- Cause RDS
- Fatal, autosomal recessive
What is unilateral pulmonary agenesis?
- one lungs
- RDS, at risk for lower reap tract infections
- 60% have other congenital anomalies (cardiac, diaphragmatic, skeletal, rib, vertebral)
What is bilateral pulmonary agenesis?
- no lungs, bronchi, vasculature.
- bronchial buds fail to develop
- fatal
What is pulmonary hypoplasia?
- small lungs. all components are present but incompletely developed.
- Associated with congenital diaphragmatic hernia
What are congenital cysts of the lung?
- cyst formed by dilation of terminal or larger bronchi
- honeycomb appearance in radiograph
- drain poorly, cause chronic infections
What is supernumerary lobes?
- extra lung lobes. Little function.
What is the septum transversum?
- divide the intraembryonic cavity into thoracic and abdominal cavity.
- incomplete division. pericarioperitoneal canals remains
- mesoderm in origin
- lungs grow in to these
What causes a congenital diaphragmatic hernia?
-failure of pleuroperitoneal folds fails to form properly, often on the left side. Causes small bowel present in the thoracic cavity, which hinders lung formation leading to pulmonary hypoplasia. Fixed surgically.
What is the function of the pleuropericardial folds?
- fuse as membranes and then formal the pleural and pericardial cavities.
What are the four components of the diaphragm?
1) septum transversum
2) pleuroperitoneal membranes
3) dorsal mesentary of the esophagus
4) Muscular ingrowt from somites at the cervical levels C3 to C5
