Respiratory Embryology

Question 1

What does the laryngotracheal groove become?

When does it develop?

Answer 1

pulmonary epithelium
glands of larynx, trachea & bronchi

week 4

Question 2

What does the splanchnic mesoderm (from lat plate) of laryngotracheal groove become?

Answer 2

CT, cartilage & smooth muscle of respiratory system (surrounds the foregut)

Question 3

Where does the lung bud come from?

Answer 3

laryngotracheal diverticulum (evagination of laryngotracheal groove)

Question 4

Why are the tracheoesophageal folds important? When do they fuse?

Answer 4

endodermal ingrowth of laryngotracheal tube that fuses to form tracheoesophageal septum (by end of week 5)

divides cranial portion of foregut & separates respiratory system from digestive system

fuse during week 5

Question 5

Where is the laryngotracheal tube located by end of week 5?

Answer 5

ventral part of foregut

primordium larynx, trachea, bronchi & lungs

Question 6

What does the dorsal part of the tracheoesophageal septum become?

Answer 6

primordium oropharynx & esophagus

Question 7

Where does the epithelial lining of the larynx come from?

Answer 7

endoderm of laryngotracheal tube

Question 8

Where do the cartilages & CT of larynx come from?

Answer 8

mesenchyme of PA 4 & 6

Question 9

What is the result of the proliferation of the laryngotracheal tube endoderm?

Answer 9

occlusion of the lumen of the tube

Question 10

When does recanalization occur and what is the result?

Answer 10

during week 10

true vocal folds & vestibular folds in the larynx

Question 11

Where does the epiglottis come from?

Answer 11

hypopharyngeal eminence (mesenchme of PA 3 & 4)

Question 12

Where do the laryngeal muscles come from?

Answer 12

myoblasts of PA 4 & 6

Question 13

What does the division of the laryngotracheal diverticulum produce?

Answer 13

trachea (late week 4/early week 5)

Question 14

Endoderm derivatives of trachea

Answer 14

tracheal epithelium
tracheal glands
pulmonary epithelium (lining of lungs)

Question 15

Splanchnic mesenchyme derivatives of trachea

Answer 15

tracheal cart (hyaline cart)
tracheal CT
tracheal smooth m

Question 16

Why is splanchnic mesenchyme important in respiratory development?

Answer 16

lung development requires SM to signal for bronchial bud branching in week 5

Question 17

Visceral pleura

Answer 17

splanchnic mesoderm of lateral plate

Question 18

Parietal pleura

Answer 18

somatic mesoderm of lateral plate

Question 19

4 stages of prenatal lung development

Answer 19

Pseudoglandular (weeks 5-17)
Canalicular (weeks 16-25)
Terminal sac (week 24-birth)
Alveolar (week 32-8yo)

Question 20

Pseudoglandular stage

Answer 20

weeks 5-17
all major elements of lung formed
no alevoli for gas exchange

fetus is NOT survivable

Question 21

Canalicular stage

Answer 21

weeks 16-25

vascularization
resp bronchioles + primordial alevolar & sacs

fetus is +/- survivable

Question 22

Terminal sac stage

Answer 22

week 24-birth

increase # of alveoli
vascularization of thin epithelium
Type 1 & Type 2 pneumocytes
lymph capillaries

survivable b/c gas xchange can occur!

Question 23

Alveolar stage

Answer 23

week 32-8yo

alveolocapillary membrane
primitive & mature alveoli (95% of alveoli mature post-natally)

Question 24

What stage of lung development is the fetus definitely survivable?

Answer 24

terminal sac stage (week 24-birth) b/c has necessary components for proper gas exchange

Question 25

How is splanchnic mesoderm critical for bronchi development?

Answer 25

as alveoli are added, need to keep developing other supporting tissue & needed for:

bronchial cartilage plates
bronchial smooth m & CT
pulmonary CT & capillaries

Question 26

Largyngeal atresia

Answer 26

failure of laryngeal recanalization in week 10

obstructed upper fetal airway

airways dilated, lungs large & filled w/ fluid, diaphragm may be flat or inverted

Question 27

Tracheoesophageal atresia

Answer 27

abnormal connection btwn trachea & esophagus due to failure of foregut endoderm to proliferate in relation to whole embryo

can’t swallow, drool, regurgitate food (GI contents can reflux thru fistula into trachea & lungs)

lung development can be impaired

Question 28

Pulmonary agensis

Answer 28

failure of splitting of R & L bronchial buds from respiratory bud

complete absence of lung or lobe & its accompanying bronchi

Question 29

Oligohydramnios

Answer 29

pulmonary hypoplasia due to insufficient amniotic fluid production (renal issue)

restricted fetal thorax from uterine pressure

clubbed feet, compressed face, issues w/ hand placement & breech position

Question 30

Respiratory Distress Syndrome

Answer 30

due to surfactant deficiency (type 2 pneumocytes can’t produce surfactant)

lungs are underinflated & alveoli appear glassy

grunting, cyanosis

Question 31

Role of surfactant

Answer 31

produced by type 2 pneumocytes

keeps surface tension @ min (btwn air/liquid interface) w/ in alveoli of lungs & prevents lung collapse during expiration

Question 32

Congenital lung cysts

Answer 32

issue w/ bronchial development due to abnormal dilation of terminal bronchi in late fetus

cysts are filled w/ fluid or air

wheezing, cyanosis, issues breathing

Question 33

Fetal Breathing Movements

Answer 33

critical for proper lung develop (conditioning of respiratory muscles)

forceful aspiration of amniotic fluid stimulates lung development

amniotic fluid is replaced by air in alveoli @ birth

Question 34

How is amniotic fluid in lungs cleared?

Answer 34

released from mouth/nose via pressure on fetal thorax during vaginal delivery

absorbed by pulmonary capillaries, arteries & veins

absorbed by lymphatics