4. Respiratory Embryology

Question 1

what does the resp system start as

Answer 1

laryngotracheal groove

Question 2

What is the relative location of the laryngotracheal groove?

Answer 2

inferior to 4th pharyngeal arches and in the floor of the cuadal foregut/primordial pharynx

Question 3

what gives rise to

pul epithelium

glands of larynx, trachea & bronchi

Answer 3

endoderm of laryngotracheal groove

Question 4

what gives rist to the CT, cartilage & smooth m in resp system

Answer 4

splanchnic mesoderm (from lateral plate)

-surrounds the foregut

Question 5

how does the globular respiratory bud form

Answer 5

anterior outgrowth from the laryngotracheal groove –> diverticulum –> continue to grow and becomes resp bud

Question 6

what is the fxn of the tracheoesophageal folds

Answer 6

grow inward, fuse & form tracheoesophageal septum (end of week 5) and pinch off (seperate esophagus & laryngotracheal tube distal laryngotracheal opening)

still invested in splanchnic mesoderm

top part stays connected and then becomes two tubes

Question 7

where does the laryngotracheal diverticulum branch off from

Answer 7

primordial pharynx

Question 8

How is the foregut divided after trachoesphageal septum is formed?

Answer 8

ventral = laryngotracheal tube (primordium of larynx, trachea, bronchi, lungs)

dorsal = primordium of oropharynx, esophagus

Question 9

what germ layer does the epithelial lining of the larynx derived from

Answer 9

endoderm of laryngotracheal tube

Question 10

what germ layer does the cartilage of the larynx derived from

Answer 10

mesenchyme of 4th & 6th pairs of PAs

NCC

Question 11

what converts the primordial glottis into a T-shaped laryngeal inlet

Answer 11

mesenchyme that produces paired arytenoid swellings

Question 12

how do the vocal folds (cords) & vestibular folds form

Answer 12

laryngeal epithelium proliferate and occlude laryngeal lumen - close off inlet

recanalization at week 10 - recreate inlet

form laryngeal ventricles bounded by folds of mucous membrane

Question 13

what does the epiglottis develop from

Answer 13

hypopharyngeal eminence

from mesenchyme of the 3-4th PAs

Question 14

what do laryngeal Ms develop from

Answer 14

myoblasts of the 4th & 6th PAs

Question 15

Which population of people are at a higher risk of choking and why?

Answer 15

Young children

Larynx is at a much higher location in children –> descends as you age (over the first 2 years)

Question 16

why is the epiglottis initially so high up in neonates

Answer 16

epiglottis moves up toward and touches soft palate when ingesting food

• helps w/ suckling reflex & makes neonates nose breathers
• able to change from liquid to solid diet as child grows bc epiglottis descends

Question 17

what is laryngeal atresia

Answer 17

rare birth defect from failure of recanalization of the larynx (very small inlet)

-obstruction of the upper fetal airway - or - congenital high airway obstruction syndrome

Question 18

what are the effects of laryngeal atresia & how is it treated

Answer 18

airways dilated, lungs enlarged & filled with fluid

diaphragm flatten or inverted –> fetal ascites &/or hydrops

treat w/ endoscopic dilation of the laryngeal web

Question 19

what germ layers form the tracheal epithelium & glands & pulmonary epithelium

Answer 19

endoderm

Question 20

what does the laryngotracheal diverticulum differentiate into

Answer 20

trachea

2 primary bronchial buds

Question 21

what germ layer forms the tracheal cartilage (hyaline), CT and M

Answer 21

splanchnic mesenchyme

Question 22

what is tracheoesophageal fistula

Answer 22

abnormal connection btn trachea & esophagus bc failure of foregut endoderm to proliferate rapidly

most common congenital anomaly of lower resp tract - 1/3000-5000

Question 23

what is esophageal atresia

Answer 23

blind esophagus

associated with 85% of tracheoesophageal fistulas

Question 24

what are symptoms of trachoesophageal fistulas

Answer 24

cant swallow

freq drool saliva

immediate regurgitation

gastic/intestinal contents reflux thru fistual to trachea & lungs

may have polyhydramnios

Question 25

what is polyhydramnios

Answer 25

excess amniotic fluid (fistula can impair this and fluid isn't removed or resorbed) USUALLY --\> fetus inhales fluid to inflate and practice breating at mid to late gestation & also swallow fluid to help GI system ==\> _usually this is resorbed back to the placenta - in this case it isnt!_

Question 26

when does the resp bud form

Answer 26

week 4

Question 27

what happens next after the resp bud

Answer 27

it grows ventrocaudally & bifurcates --\> makes primary bronchial buds -these then grow laterally into pericardioperitoneal canals

Question 28

when do the primary bronchial buds branch & what do they form

Answer 28

beginning of week 5 secondary bronchial buds --\> tertiary bronchial buds

Question 29

what regulates the branching pattern of the lung endoderm

Answer 29

splanchnic mesoderm

Question 30

what are bronchopulmonary segments & when are they formed

Answer 30

segmental bronchi & mesenchyme week 7

Question 31

what germ layer is the origin of the visceral pleura

Answer 31

splanchnic portion of the lateral plate mesoderm

Question 32

what is the germ layer origin of parietal pleura

Answer 32

somatic portion of the lateral plate mesoderm

Question 33

what are the 4 steps of lung maturation

Answer 33

1. pseudoglandular (week 5-17) 2. canalicular (week 16-25) 3. terminal sac (week 24 to birth) 4. alveolar (week 32- 8 yrs)

Question 34

what occurs in the pseudoglandular phase

Answer 34

week 5-17 histologically looks like exocrine gland form all major elements of lung EXCEPT those involved in gas exchange -born at this time - fetus cannot survive

Question 35

what happens in the canalicular phase

Answer 35

week 16-25 vascularization resp bronchioles primordial aleveolar & sacs present (primitive alevoli) born now: +/- survive

Question 36

what happens in the terminal sac phase

Answer 36

week 24 to birth form numerous alveoli -thin epithelium w/ increased vascularization (type I & II pneumocytes & lymphatic capillaries) gas exchange starts to occur born now: survivable

Question 37

what happens in alveolar phase

Answer 37

week 32 to 8 years alveolocapillary membrane primitive alveoli form more primitive alveoli mature alveoli (around 95% alveoli mature postnatally)

Question 38

why is splanchnic mesoderm critical as the bronchi develop

Answer 38

make : 1. cartilaginous plates (bronchial) 2. bronchial smooth M & CT 3. pul CT & capillaries

Question 39

How are new alveoli added until 8 years of age?

Answer 39

a primitive alveoli may be split by a septa creating 2 alveoli. Mature alveoli CANNOT be split, only primitive

Question 40

What is the purpose of fetal breathing movements?

Answer 40

essential for normal lung development used for fetal monitoring during development Causes some aspiration of amniotic fluid

Question 41

How is amniotic fluid cleared from the lungs at birth?

Answer 41

pressure during vaginal delivery, suction, and absorbed by lymphatics, capillaries, arteries, and veins

Question 42

What is pulmonary agenesis?

Answer 42

Complete Absence of Lungs, Bronchi, and Vasculature. Respiratory bud fails to split into left and right bronchial buds

Question 43

What is pulmonary hypoplasia?

Answer 43

underdevelopment of the lungs due to uterine pressure on the the fetal thorax Commonly caused by oligohydramnios, especially if it occurs \<26 weeks

Question 44

What is oligohydramnios?

Answer 44

insufficient amniotic fluid production (\<500mL) Typically associated with renal agenesis or failure

Question 45

What is the oligohydramnios (Potters) sequence?

Answer 45

clubbed feet hand position defects pulm hypoplasia breech position cranial anomalies related to oligohydramnios

Question 46

What is respiratory distress syndrome?

Answer 46

absence of lung surfactant in premature infants due to a defect in type 2 alveolar cells Previously called hyaline membrane disease due to glassy appearance

Question 47

What are the signs of respiratory distress syndrome?

Answer 47

tachypnea, nasal flaring, suprasternal, intercostal, or subcostal retractions, grunting, and cyanosis

Question 48

What are congenital lung cysts?

Answer 48

cysts filled with fluid or air thought to be formed by the abnormal dilation of terminal bronchi May cause wheezing, cyanosis, and difficulty breathing.