4. Respiratory Embryology Flashcards
what does the resp system start as
laryngotracheal groove
What is the relative location of the laryngotracheal groove?
inferior to 4th pharyngeal arches and in the floor of the cuadal foregut/primordial pharynx
what gives rise to
pul epithelium
glands of larynx, trachea & bronchi
endoderm of laryngotracheal groove
what gives rist to the CT, cartilage & smooth m in resp system
splanchnic mesoderm (from lateral plate)
-surrounds the foregut
how does the globular respiratory bud form
anterior outgrowth from the laryngotracheal groove –> diverticulum –> continue to grow and becomes resp bud
what is the fxn of the tracheoesophageal folds
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
where does the laryngotracheal diverticulum branch off from
primordial pharynx
How is the foregut divided after trachoesphageal septum is formed?
ventral = laryngotracheal tube (primordium of larynx, trachea, bronchi, lungs)
dorsal = primordium of oropharynx, esophagus
what germ layer does the epithelial lining of the larynx derived from
endoderm of laryngotracheal tube
what germ layer does the cartilage of the larynx derived from
mesenchyme of 4th & 6th pairs of PAs
NCC
what converts the primordial glottis into a T-shaped laryngeal inlet
mesenchyme that produces paired arytenoid swellings
how do the vocal folds (cords) & vestibular folds form
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
what does the epiglottis develop from
hypopharyngeal eminence
from mesenchyme of the 3-4th PAs
what do laryngeal Ms develop from
myoblasts of the 4th & 6th PAs
Which population of people are at a higher risk of choking and why?
Young children
Larynx is at a much higher location in children –> descends as you age (over the first 2 years)
why is the epiglottis initially so high up in neonates
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
what is laryngeal atresia
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
what are the effects of laryngeal atresia & how is it treated
airways dilated, lungs enlarged & filled with fluid
diaphragm flatten or inverted –> fetal ascites &/or hydrops
treat w/ endoscopic dilation of the laryngeal web
what germ layers form the tracheal epithelium & glands & pulmonary epithelium
endoderm
what does the laryngotracheal diverticulum differentiate into
trachea
2 primary bronchial buds
what germ layer forms the tracheal cartilage (hyaline), CT and M
splanchnic mesenchyme
what is tracheoesophageal fistula
abnormal connection btn trachea & esophagus bc failure of foregut endoderm to proliferate rapidly
most common congenital anomaly of lower resp tract - 1/3000-5000
what is esophageal atresia
blind esophagus
associated with 85% of tracheoesophageal fistulas
what are symptoms of trachoesophageal fistulas
cant swallow
freq drool saliva
immediate regurgitation
gastic/intestinal contents reflux thru fistual to trachea & lungs
may have polyhydramnios
what is polyhydramnios
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!
when does the resp bud form
week 4
what happens next after the resp bud
it grows ventrocaudally & bifurcates –> makes primary bronchial buds
-these then grow laterally into pericardioperitoneal canals
when do the primary bronchial buds branch & what do they form
beginning of week 5
secondary bronchial buds –> tertiary bronchial buds
what regulates the branching pattern of the lung endoderm
splanchnic mesoderm
what are bronchopulmonary segments & when are they formed
segmental bronchi & mesenchyme
week 7
what germ layer is the origin of the visceral pleura
splanchnic portion of the lateral plate mesoderm
what is the germ layer origin of parietal pleura
somatic portion of the lateral plate mesoderm
what are the 4 steps of lung maturation
- pseudoglandular (week 5-17)
- canalicular (week 16-25)
- terminal sac (week 24 to birth)
- alveolar (week 32- 8 yrs)
what occurs in the pseudoglandular phase
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
what happens in the canalicular phase
week 16-25
vascularization
resp bronchioles
primordial aleveolar & sacs present (primitive alevoli)
born now: +/- survive
what happens in the terminal sac phase
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
what happens in alveolar phase
week 32 to 8 years
alveolocapillary membrane
primitive alveoli
form more primitive alveoli
mature alveoli
(around 95% alveoli mature postnatally)
why is splanchnic mesoderm critical as the bronchi develop
make :
- cartilaginous plates (bronchial)
- bronchial smooth M & CT
- pul CT & capillaries
How are new alveoli added until 8 years of age?
a primitive alveoli may be split by a septa creating 2 alveoli. Mature alveoli CANNOT be split, only primitive
What is the purpose of fetal breathing movements?
essential for normal lung development
used for fetal monitoring during development
Causes some aspiration of amniotic fluid
How is amniotic fluid cleared from the lungs at birth?
pressure during vaginal delivery, suction, and absorbed by lymphatics, capillaries, arteries, and veins
What is pulmonary agenesis?
Complete Absence of Lungs, Bronchi, and Vasculature. Respiratory bud fails to split into left and right bronchial buds
What is pulmonary hypoplasia?
underdevelopment of the lungs due to uterine pressure on the the fetal thorax
Commonly caused by oligohydramnios, especially if it occurs <26 weeks
What is oligohydramnios?
insufficient amniotic fluid production (<500mL)
Typically associated with renal agenesis or failure
What is the oligohydramnios (Potters) sequence?
clubbed feet
hand position defects
pulm hypoplasia
breech position
cranial anomalies related to oligohydramnios
What is respiratory distress syndrome?
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
What are the signs of respiratory distress syndrome?
tachypnea, nasal flaring, suprasternal, intercostal, or subcostal retractions, grunting, and cyanosis
What are congenital lung cysts?
cysts filled with fluid or air
thought to be formed by the abnormal dilation of terminal bronchi
May cause wheezing, cyanosis, and difficulty breathing.
