Respiratory Embryology Flashcards
What does the respiratory system start off as?
A median outgrowth known as the laryngotracheal groove
What will evagination of the laryngotracheal groove form?
Laryngotracheal diverticulum (lung bud)
Where is the laryngotracheal groove found?
In floor of caudal end of foregut/primordial pharynx
Inferior to 4th pAs
Where will the primordium of Tracheobronchioal tree develop?
Caudal to 4th pharyngeal pouches
What does the endoderm of laryngotracheal groove form?
Pulmonary epithelium
Glands of larynx
Trachea
Bronchi
In the resp. System, what does the splanchnic mesoderm from lateral plate form?
What does it surround?
Will form the CT, cartilage, and Smooth m. In respiratory system structures
Surrounds the foregut
What will happen as the laryngotracheal diverticulum (lung bud) do as it elongates?
Becomes invested w/ splanchnic mesoderm, forms respiratory bud
(Remember, the lung buds are what makes IE and EE coelom separate)
What is the origitn of the respiratory tree?
Respiratory bud
When will the tracheo-esophageal septum form?
How?
At end of wk 5
From the development and fusion of tracheo-esophageal folds
What does the tracheo-esophageal septum do?
Divides esophagus from laryngotrachela tube
What is the ventral and dorsal portion of the foregut divided into?
Ventral part = laryngotracheal tube
Dorsal part = primordium of oropharynx, esophagus
What will the laryngotracheal tube form?
Larynx
Trachea
Bronchi
Lungs
What is the embryonic origin of the
Epithelial lining of the larynx?
Endoderm of the laryngotracheal tube (cranial end)
What occluded the laryngeal lumen?
Proliferation of the laryngeal epithelium
How are laryngeal ventricles formed?
When?
Via recanalization of the occluded lumen
Week 10
How are vocal folds/cord and vestibular folds formed?
Formed by the bounding of the laryngeal ventricles by folds of mucous membrane
What is the embryonic origin of the
Cartilage of the larynx?
Mesenchyme of the 4th and 6th pairs of pharyngeal arches
NCC derived
What produced the paired arytenoid swellings of the larynx?
Mesenchyme
What is the primordial glottis converted into? F
T-shaped laryngeal inlet
What does the epiglottis develop form?
Hypopharyngeal eminence
What is the embryonic origin of the epiglottis?
Mesenchyme of PAs 3 and 4
What is the embryonic origin of the laryngeal ms?
Myoblasts of PAs 4 and 6
Wher si the larynx located in a neonate?
Epiglottis?
High in neck
Epiglottis in contact w/ soft palate - allowing for separate respiratory and digestive tracts
Why is the larynx positioned high in the neck of a neonate?
Helps breast feeding
Makes infants obligatory nose breathers
When will the larynx descend in the neck?
Over the first 2 years of life
What is laryngeal atresia?
Birth defects resulting form the FAILURE of recanalization of larynx
What are the symptoms of laryngeal atresia?
- Obstruction of upper fetal airway or congenital high airway obstruction syndrome (CHAOS syndrome)
- Airways become dilated, lungs enlarged and filled w/ fluid
- Diaphragm flattened or inverted, & there is fetal ascites and/or hydrops
What is the treatment for Laryngeal atresia?
Endoscopic dilation of laryngeal web
What does the trachea form from?
Laryngotracheal diverticulum (lung bud)
What are the endodermal components of the trachea?
Tracheal epithelium
Glands
Pulmonary epithelium
Histologically, what is the pulmonary epithelium and tracheal epithelium of the trachea?
Pseudo-stratified columnar ciliated epithelium
What are the mesodermal components of the trachea?
Splanchnic mesenchyme makes …
Tracheal cartilages (hyaline)
CT
Muscle
What do the lungs develop?
Laryngotracheal diverticulum —> primary bronchial buds (and trachea)
When will the laryngotracheal diverticulum enlarge to form the respiratory bud?
Week 4
What happens to the respiratory buds formed by the laryngotracheal diverticulum?
Grow ventrocaudally and bifurcate
Form primary bronchial buds
How do the Primary Bronchial Buds grow?
When do they branch?
Grow laterally into Pericardioperitoneal canal
Branch at beginning of 5th week into secondary bronchial buds
What will secondary bronchial buds brnach into?
Tertiary bronchial buds f
What regulates the branching pattern of lung endoderm?
Splanchnic mesenchyme
What is the branching pattern of lung endoderm dependent on?
Induction (tissue signaling0
When do bronchopulmonary segments form?
7th week
What are bronchopulmonary segments made up of?
Segmental bronchi + mesenchyme
What will lungs acquire as they develop?
Layer of visceral pleura
What is visceral plerua fromed from?
Splanchnic portion of lateral plate mesenchyme
What is parietal pleura formed form?
Somatic portion of lateral plate mesoderm
What will the parietal plerua line?
Thoracic body wall
What are the 4 stages of prenatal lung development?
Pseudoglandular
Canalicular
Terminal sac
Alveolar
When is the lung in the pseudoglandular stage?
Weeks 5-17
When are the lungs in the Canalicular stage?
Wks 16-25
When are the lungs in the Terminal Sac stage?
Wks 24-birth
When are the lungs in the alveolar stage?
Wks 32 - 8 years
What characterizes the Pseudoglandular stage of Lung Maturation?
Lungs look like exocrine glands
All major elements of the lung have formed; except those involved w/ gas exchange
What characterizes the Canalicular stage of Lung Maturation?
Overlaps the pseudoglandular stage
Vascularization of lungs
Repsiratory bronchioles (capable of gas exchange)
Primordial alveolar and sac present (primitive alveoli)
Are fetuses able to survive in the pseudoglandular stage?
No
Are fetuses able to survive in the Canalicular stage?
Maybe
What characterizes the Terminal Sac stage of Lung Maturation?
Numerous alveoli form
Thin epithelium w/ increased vascularization
Has type 1 and 2 pneumocytes
Lymphatic capillaries
Are fetuses able to survive in the terminal sac stage?
Yes
What produces type 1 pneumocytes?
Type 2
What is the role of type 2 pneumocytes?
Produce surfactant
What characterizes the Alveolar stage of Lung Maturation?
Alveolocapillary membrane
Primitive alveoli formed and forming
Mature alveoli
When do most mature alveoli develop?
~85% develop postnatally
When is alveolar development largely completed by?
When are they added until?
Mostly completed by 3 years
Added until 8 years of age
What 3 things does SPlanchnic mesoderm form that is critical for bronchi?
- Cartilaginous plates (bronchial)
- Bronchial SM and CT
- Pulmonary CT and capillaries
What is essential for normal lung development?
Fetal breathing movements
What are Fetal Breathing movements (FBM)?
Intermittent pattern that conditions respiratory muscles and cause aspiration of amniotic fluid helping to stimulate lung development
How can FBMs be used?
Used during fetal monitoring and as predictors of fetal outcome in pre-term delivery
How is intra-alveolar fluid of the lung replaced w/ air at birth? (3 ways)
Aeration of the lungs is achieved by
- Released via mouth/nose as pressure occurs on fetal thorax during vaginal delivery
- Cleared by pulmonary capillaries, arteries, and veins
- Cleared by lymphatics
What is surfactant produced by?
Type 2 alveolar cells
What are the consequences of surfactant not being present?
Under inflated lungs
Tachypnea
Nasal flaring
Suprasternal, intercostal, or subcostal retractions
Grunting/cyanosis
What is a tracheo-esophageal fistula?
Occurrence rate?
Assoc. w/?
Abnormal connection b/w trachea and esophagus
1: 3000-5000 births
85% assoc. w/ esophageal atresia (blind esophagus)
What is the cause of trachea-esophageal fistula?
Failure of foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo
What is the most common congenital anomaly of the lower repsiratory tract?
Trachea-esophageal fistula
What are the symptoms of a tracheoesophageal fistula?
- Cannot swallow, frequently drool saliva, immediate regurgitations when fed
- Gastric and intestinal contents may also reflux thru the fistula into the trachea and lungs
• Polyhydramnios: xs amniotic fluid
◦ Cannot enter stomach/intestines for absorption
◦ Not transferred for disposal via the placenta
• excess air in GI tract
What is polyhydramnios?
Excess amniotic fluid
What is pulmonary agenesis?
Occurrence?
Unilateral agenesis or complete absence of a lung or a lobe and accompanying bronchi
1:15,000
What is the cause of PUlmonary Agenesis?
Failure of respiratory buds to split into R/L bronchial buds
What is oligohydramnios?
Assoc. w/?
Insufficient amniotic fluid production (<500 mL)
Assoc. w/ renal agenesis or failure
What are the consequences of severe and chronic oligohydramnios?
Retarded lung development due to lack of counter pressure against uterine pressure
(Remember the FBMs)
What is pulmonary hypoplasia?
Occurrence?
Restriction of fetal thorax due to uterine pressure and decreased hydraulic pressure on lungs affecting stretch receptors and lung growth
14:10,000 births
What increase the risk of pulmonary hypoplasia?
Significant increase in risk if olgiohydramnios present at <26 Wks
What is oligohydramnios sequence?
Potter facies Limb hypoplasia Decreased amniotic fluid Nasal flaring Nasal bridge wide Renal failure in fetus Club feet Etc.
What is Respiratory Distress syndrome?
% affects?
Rapid labored breathing that develops shortly after birth
2% of neonates affected
Accounts for 50-70% of deaths in premature infants
What is a major cause of RDS?
Surfactant deficiency
How will a surfactant deficiency leading to RDS presents?
- Lungs are under inflated
- Alveoli contain a fluid that resembles a glassy membrane (hyaline membrane disease)
- Irreversible changes int he type 2 alveolar cells, making them incapable of producing surfactant
What are the symptoms of RDS?
Tachypnea, nasal flaring
Suprasternal, intercostal, or subcostal retractions
Grunting and Cyanosis
What are congenital lung cycsts
Cysts filled w/ fluid or air thought rob e formed by dilation of terminal bronchi
What causes congential lung cysts?
Disturbances in bronchial development during late fetal life
Sxs of congenital lung cysts?
Wheezing, cyanosis, difficulty breathing
