Respiratory Embryology

Question 1

Respiratory system starts as

Answer 1

A median outgrowth known as the laryngotracheal groove

Found in floor of caudal end of foregut/primordial pharynx, inferior to 4th pharyngeal arch

Question 2

Primordium of tracheobronchial tree develops where

Answer 2

Caudal to 4th pharyngeal pouch

Question 3

Endoderm of laryngotracheal groove gives rise to

Answer 3

Pulmonary epithelium and glands of larynx, trachea and bronchi

Question 4

Splanchnic mesoderm (from lateral plate) gives rise to

Answer 4

CT, cartilage, and smooth muscle in larynx, trachea and bronchi
Surrounds foregut

Question 5

Laryngotracheal groove will evaginate to form

Answer 5

Laryngotracheal diverticulum (lung bud)

Question 6

What gives rise to the respiratory bud

Answer 6

The diverticulum elongates and the distal end enlarges to form the globular respiratory bud

Question 7

How is the trachea and esophagus separated

Answer 7

Tracheoesophageal folds fuse and form the tracheoesophageal septum at 5 weeks

Question 8

Dorsal portion of foregut forms

Answer 8

Primordium of oropharynx, esophagus

Question 9

Ventral part of foregut forms

Answer 9

Laryngotracheal tube (primordium of larynx, trachea, bronchi and lungs

Question 10

Epithelial lining of larynx comes from

Answer 10

Endoderm of laryngotracheal tube

Question 11

Cartilages of larynx come from

Answer 11

Mesenchyme of 4th/6th pharyngeal arches (NCC derived)

Question 12

Arytenoid swellings arise from

Answer 12

Mesenchyme

Question 13

Epiglottis develops from

Answer 13

Hypopharyngeal eminence, produced by mesenchyme of 3/4th pharyngeal arches

Question 14

Recanalization of larynx

Answer 14

Laryngeal epithelium proliferates and occludes laryngeal lumen by the 10th week

Question 15

Laryngeal atresia

Answer 15

Failure of recanalization of the larynx
Obstruction of the upper fetal airway (CHAOS- congenital high airway obstruction syndrome)
Airways become dilated, lungs are enlarged and filled with fluid
Diaphragm flattened or inverted, and there is fetal ascites and/or hydrops

Question 16

Tracheal development

Answer 16

Laryngeotracheal diverticulum forms trachea and primary bronchial buds
Endoderm differentiates into tracheal epithelium and glands, and pulmonary epithelium
Splanchnic mesoderm forms tracheal cartilages, CT and muscle

Question 17

Tracheoesophageal fistula

Answer 17

Abnormal connection b/w trachea and esophagus
Many cases are associated with esophageal atresia, blind esophagus
Failure of foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo

Question 18

Tracheoesophageal fistula symptoms

Answer 18

Cannot swallow, frequently drool saliva, immediate regurgitation when fed
Polyhydramnios- excess amniotic fluid
-cannot enter the stomach/intestines for absorption
-not transferred for disposal via the placenta

Question 19

Respiratory buds form when and from what

Answer 19

Form during 4th week from enlargement of the distal end of the laryngotracheal diverticulum

Question 20

What regulates the branching pattern of the lung endoderm

Answer 20

Splanchnic mesenchyme

Question 21

Primary bronchial buds and bronchopulmonary segments form when

Answer 21

Primary- week 5

BP segments- week 7

Question 22

Lungs later acquire a layer of

Answer 22

Visceral pleura (from splanchnic portion of lateral plate mesenchyme)

Question 23

Thoracic body wall becomes lined by a layer of

Answer 23

Parietal pleura (somatic portion of lateral plate mesoderm)

Question 24

Psuedoglandular stage of lung maturation

Answer 24

Weeks 5-17
Looks like exocrine glands
All major elements of the lung have formed, except those involved with gas exchange
Fetus cannot survive

Question 25

Canalicular stage of lung maturation

Answer 25

16-25 weeks
Overlaps pseudoglandular
Vascularization
Respiratory bronchioles
Primordial alveolar & sacs present (primitive alveoli)
May be able to survive

Question 26

Terminal sac stage of lung maturation

Answer 26

24 weeks-birth
Numerous alveoli form
Thin epithelium w/increased vascularization
Type 1/2 pneumocytes (type 2 are surfactant producing)
Lymphatic capillaries
Gas exchange can occur, survivable

Question 27

Alveolar stage of lung maturation

Answer 27

32wks-8years
Alveolocapillary membrane
Primitive alveoli
Form more primitive alveoli
95% of alveoli develop postnatally
Mature alveoli may form until ~8 years

Question 28

Splanchnic mesoderm importance in bronchi development

Answer 28

Critical for formation of:
Cartilaginous plates
Bronchial smooth muscle and CT
Pulmonary CT and capillaries

Question 29

Fetal breathing movements

Answer 29

Required for normal lung development
Conditions respiratory muscles
Aeration of lungs requires rapid replacement of intra-alveolar fluid with air

Question 30

Pulmonary agenesis

Answer 30

Unilateral- complete absence of a lung or a lobe and accompanying bronchi
Respiratory bud fails to split into R/L bronchial buds

Question 31

Oligohydramnios

Answer 31

Insufficient amniotic fluid production
Typically associated with renal agenesis or failure
Severe and chronic oligohydramnios retards lung development

Question 32

Pulmonary hypoplasia

Answer 32

Restriction of fetal thorax (from uterine pressure)
Decreased hydraulic pressure on lungs
Affects stretch receptors and lung growth
Risk increases significantly with oligohydramnios <26 weeks

Question 33

Respiratory distress syndrome

Answer 33

Rapid, labored breathing shortly after birth
Significant cause of death in premature infants
Surfactant deficiency is a major cause:
-lungs are underinflated
-alveoli contain fluid that resembles glassy membrane
-irreversible changes in type II alveolar cells so they cant produce surfactant

Question 34

Signs/symptoms of RDS

Answer 34

Tachypnea, nasal flaring
Suprasternal, intercostal or subcostal retractions
Grunting and cyanosis

Question 35

Congenital lung cysts

Answer 35

Filled with fluid or air
Thought to be formed by the dilation of terminal bronchi
Disturbance in bronchial development during late fetal life
May exhibit wheezing, cyanosis or difficulty breathing