Respiratory Embryology

Question 1

Starts as a median outgrowth

Answer 1

laryngotracheal groove,
Found in the floor of the caudal end of
the foregut/primordial pharynx

Question 2

Primordium of tracheobronchial

tree

Answer 2

develops caudal to 4th

pharyngeal pouches

Question 3

Endoderm of laryngotracheal

groove

Answer 3

pulmonary epithelium
& glands of larynx, trachea, &
bronchi

Question 4

Splanchnic mesoderm

from lateral plate

Answer 4

CT,
cartilage, & smooth muscle in
these structures – surrounds
the foregut

Question 5

Laryngotracheal groove

will evaginate to form

Answer 5

laryngotracheal

diverticulum (lung bud)

Question 6

Diverticulum elongates &

Answer 6

invested w/ splanchnic

mesenchyme

Question 7

Distal end enlarges to form a

globular

Answer 7

respiratory bud,

origin of respiratory tree

Question 8

Tracheoesophageal folds

develop

Answer 8

fuse to form the
tracheoesophageal septum
(end 5th week)

Question 9

Divides the cranial portion of the foregut:

Answer 9

• Ventral part = laryngotracheal tube (primordium of
larynx, trachea, bronchi, lungs)
• Dorsal part = primordium of oropharynx, esophagus

Question 10

Epithelial lining of larynx

Answer 10

= endoderm of
laryngotracheal tube (cranial end)

Question 11

Cartilages of larynx=

Answer 11

mesenchyme of 4th &

6th pairs of PAs (NCC derived)

Question 12

Mesenchyme produces paired

arytenoid swellings

Answer 12

• Convert primordial glottis into

a T -shaped laryngeal inlet

Question 13

Laryngeal epithelium proliferates

& occludes

Answer 13

laryngeal lumen

• Recanalization occurs by 10th
week

Question 14

Laryngeal ventricles form during recanalization →

Answer 14

bounded by folds of mucous membrane to form vocal

folds (cords) & vestibular folds

Question 15

Epiglottis develops from

Answer 15

hypopharyngeal eminence
• Produced from
mesenchyme of the 3-4th
PAs

Question 16

Laryngeal muscles develop from

Answer 16

myoblasts of 4th & 6th PAs

Question 17

Larynx is in a high position in

Answer 17

the neck of the neonate

Question 18

Epiglottis in contact w/ soft palate →

Answer 18

separate respiratory & digestive tracts

Question 19

Laryngeal descent occurs over

Answer 19

the first 2 years

Question 20

Laryngeal atresia

Answer 20

Rare birth defect, resulting from failure of
recanalization of the larynx

Obstruction of the upper fetal airway, or
congenital high airway obstruction syndrome
(CHAOS syndrome)
• Airways become dilated, lungs are enlarged &
filled with fluid
• Diaphragm flattened or inverted, & there is
fetal ascites and/or hydrops
• Treatment is by endoscopic dilation of the
laryngeal web.

Question 21

Laryngotracheal

diverticulum →

Answer 21

trachea & primary
bronchial buds (2)

Question 22

Endoderm →

Answer 22

differentiates
into the tracheal epithelium
& glands, & pulmonary
epithelium

Question 23

Splanchnic mesenchyme

→

Answer 23

tracheal cartilages, CT, &

muscle

Question 24

Tracheoesophageal

fistula:

Answer 24

an abnormal
connection between
trachea & esophagus

Most common
congenital anomaly of
the lower respiratory
tract

85% of cases associated with
esophageal atresia, blind
esophagus

Failure of foregut endoderm to proliferate rapidly
enough in relation to the rest of the embryo

Question 25

Tracheoesophageal fistula symptoms

Answer 25

Cannot swallow, frequently drool saliva, immediate regurgitation when fed • Gastric & intestinal contents may also reflux through the fistula into the trachea and lungs • Polyhydramnios: excess amniotic fluid • Cannot enter the stomach/intestines for absorption • Not transferred for disposal via the placenta

Question 26

Distal end of laryngotracheal diverticulum enlarges to form

Answer 26

the respiratory bud (4th week)

Question 27

Bud grows ventrocaudally & bifurcates, forming

Answer 27

primary bronchial buds

Question 28

Buds grow laterally into

Answer 28

pericardioperitoneal canals

Question 29

Primary bronchial buds branch (begins 5th wk) to form

Answer 29

secondary bronchial buds → tertiary bronchial buds

Question 30

Branching pattern of the lung endoderm is regulated by

Answer 30

splanchnic mesenchyme

Question 31

Bronchopulmonary segments (7th week) =

Answer 31

segmental bronchi + mesenchyme

Question 32

path of development

Answer 32

Main bronchi → secondary bronchi → lobar → segmental → intrasegmental branches

Question 33

As lungs develop, they acquire a | layer of

Answer 33

visceral pleura (splanchnic portion of lateral plate mesenchyme)

Question 34

• Lungs & pleural cavities grow | caudally into the

Answer 34

mesenchyme of the body wall • Will lie close to the heart

Question 35

Thoracic body wall becomes lined | by a layer of

Answer 35

parietal pleura (somatic portion of lateral plate mesoderm)

Question 36

• Pseudoglandular (5-17wks) lung maturation

Answer 36

``` • Looks like exocrine glands • All major elements of the lung have formed, except those involved with gas exchange • Fetus cannot survive ```

Question 37

Canalicular (16-25wks) lung maturation

Answer 37

``` • Overlaps pseudoglandular • Vascularization • Respiratory bronchioles • Primordial alveolar & sacs present (primitive alveoli) • +/- surviva ```

Question 38

Terminal sac (24wks-birth) lung maturation

Answer 38

``` • Numerous alveoli form • Thin epithelium w/increased vascularization • Type I pneumocytes • Type II pneumocytes (surfactant) • Lymphatic capillaries • Gas exchange can occur • Survivable ```

Question 39

• Alveolar (32wks - 8yrs) lung maturation

Answer 39

* Alveolocapillary membrane * Primitive alveoli * Form more primitive alveoli * Mature alveoli

Question 40

As the bronchi develop, splanchnic | mesoderm is critical:

Answer 40

``` esoderm is critical: 1. Cartilaginous plates (bronchial) 2. Bronchial smooth muscle & connective tissue 3. Pulmonary connective tissue & capillaries are also derived from this tissue ```

Question 41

Fetal Breathing Movements (FBMs)

Answer 41

• Essential for normal lung development • Intermittent pattern that conditions respiratory muscles • Used during fetal monitoring & as a predictor of fetal outcome in preterm delivery • Forceful enough to cause aspiration of amniotic fluid • Helps to stimulate lung development • At birth, aeration of the lungs requires rapid replacement of intra-alveolar fluid with air

Question 42

FBMs Cleared via:

Answer 42

1. Released from mouth/nose by pressure on the fetal thorax during vaginal delivery 2. Pulmonary capillaries, arteries, & veins 3. Lymphatics

Question 43

Pulmonary agenesis

Answer 43

``` • Complete absence of a lung or a lobe & accompanying bronchi • Respiratory bud fails to split into R/L bronchial buds • Unilateral agenesis ```

Question 44

Oligohydramnios

Answer 44

``` • Insufficient amniotic fluid production (<500mL) • Severe & chronic oligohydramnios retards lung development • Pulmonary hypoplasia → restriction of fetal thorax (from uterine pressure) • 14:10,000 births • Decreased hydraulic pressure on the lungs • Affects stretch receptors & lung growth • Risks increases significantly with oligohydramnios <26wks ```

Question 45

Respiratory Distress Syndrome

Answer 45

• Rapid, labored breathing develops shortly after birth • Affects approximately 2% of neonates; accounts for 50-70% deaths in premature infants • Surfactant deficiency is a major cause of RDS: • Lungs are underinflated • Alveoli contain a fluid that resembles a glassy membrane (hyaline membrane disease) • Irreversible changes in the type II alveolar cells, making them incapable of producing surfactant • Signs and symptoms • Tachypnea, nasal flaring • Suprasternal, intercostal, or subcostal retractions • Grunting & cyanosis

Question 46

Congenital Lung Cysts

Answer 46

``` • 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, difficulty breathing ```