Embryology of respiratory system

Question 1

When does the respiratory diverticulum form?

Answer 1

week 4, appears day 22

Question 2

What does the tracheo-esophageal ridge separate?

Answer 2

the esophagus, and trachea/lung bud

Question 3

What is the origin of the epithelium of the lining of the larynx, trachea, bronchi, and lungs?

Answer 3

Endodermal (foregut)

Question 4

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?

Answer 4

1) Splanchnic mesoderm surrounding the foregut

2) tracheal cartilages are derived form neural crest cells

Question 5

What is a trachea-esophageal fistula?

Answer 5

Abnormal communications between the trachea and esophagus due to incomplete division of foregut

Question 6

What is a complication of trachea-esophageal fistula?

Answer 6

Polyhydromnios, since amniontic fluid does not pass down into the stomach and intestine

Question 7

Tracheo-esophageal fistula with Esophageal atresia

Answer 7

Upper esophagus ends abruptly; lower esophagus forms fistula with trachea. Abdomen distension from air in stomach. Milk may be driven into respiratory system.

Question 8

What is H-type fistula?

Answer 8

Fistula between trachea and esophagus. Milk may be driven into resp system

Question 9

What anomalies or defects are associated with TEF?

Answer 9

V - vertebral
A - Anal atresia
C - Cardiac
T - tracheo esophageal fistulas
E - Esophageal atresea
R - renal
L - limb

Question 10

When does formations of main and secondary bronchi usually happen?

Answer 10

week 5

Question 11

Which main bronchus do foreign objects are likely to get lodge?

Answer 11

Right main bronchus because it descends more vertical and has a larger lumen

Question 12

How many tertiary or segmental bronchi form in the right and left lungs?

Answer 12

right - 10

left - 8-10 (Nunn’s notes has the combined form apico-posterior, and antero-medial basal)

Question 13

What regulates the bronchi branching?

Answer 13

-regulated by epithelial-mesenchymal interactions between the endoderm of the lung bud and the splanchic mesoderm that surrounds them

Question 14

What forms the pleura?

Answer 14

Splanchnic mesoderm form visceral pleura

Somatic mesoderm form parietal pleura

Question 15

What are the 4 periods of lung maturation? What are the relative time frames?

Answer 15

1) Pseudoglandular - 5-17 wks
2) Canalicular - 16 - 25 (28) wks
3) Terminal Sac - 24-birth
4) Alveolar -Birth to 8 years

Question 16

What occurs in pseudoglandular period?

Answer 16

-terminal bronchioles form. Respiration not possible.

Question 17

What occurs in canalicular period?

Answer 17

• 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.

Question 18

What occurs in terminal sac period?

Answer 18

• 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.

Question 19

What is the function of surfactant?

Answer 19

-forms a film over internal walls of terminal sacs, which decreases surface tension thus facilitating inflation and prevent collapse of alveoli during expiration

Question 20

What occurs in the alveolar period?

Answer 20

• increase number of resp bronchioles and alveoli. 95% of mature alveoli do not develop until after birth

Question 21

What is atelectasis?

Answer 21

collapse of alveoli during expiration

Question 22

What happens to lung fluid during birth?

Answer 22

1) absorbed by blood and lymph capillaries

2) expelled via trachea and bronchi during delivery

Question 23

What causes bronchopulmonary dysplasia?

Answer 23

dysplasia or abnormal formation can be caused by chronic lung injury in preterm infants

Question 24

What is respiratory distress syndrome (RDS)?

Answer 24

• 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

Question 25

Treatment for respiratory distress syndrome in premature neonates.

Answer 25

• 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.

Question 26

what is surfactant B deficiency disease?

Answer 26

• Cause RDS

- Fatal, autosomal recessive

Question 27

What is unilateral pulmonary agenesis?

Answer 27

• one lungs
• RDS, at risk for lower reap tract infections
• 60% have other congenital anomalies (cardiac, diaphragmatic, skeletal, rib, vertebral)

Question 28

What is bilateral pulmonary agenesis?

Answer 28

• no lungs, bronchi, vasculature.
• bronchial buds fail to develop
• fatal

Question 29

What is pulmonary hypoplasia?

Answer 29

• small lungs. all components are present but incompletely developed.
• Associated with congenital diaphragmatic hernia

Question 30

What are congenital cysts of the lung?

Answer 30

• cyst formed by dilation of terminal or larger bronchi
• honeycomb appearance in radiograph
• drain poorly, cause chronic infections

Question 31

What is supernumerary lobes?

Answer 31

• extra lung lobes. Little function.

Question 32

What is the septum transversum?

Answer 32

• divide the intraembryonic cavity into thoracic and abdominal cavity.
• incomplete division. pericarioperitoneal canals remains
• mesoderm in origin
• lungs grow in to these

Question 33

What causes a congenital diaphragmatic hernia?

Answer 33

-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.

Question 34

What is the function of the pleuropericardial folds?

Answer 34

• fuse as membranes and then formal the pleural and pericardial cavities.

Question 35

What are the four components of the diaphragm?

Answer 35

1) septum transversum
2) pleuroperitoneal membranes
3) dorsal mesentary of the esophagus
4) Muscular ingrowt from somites at the cervical levels C3 to C5