Respiratory Embryology Flashcards
Respiratory system starts as
A median outgrowth known as the laryngotracheal groove
Found in floor of caudal end of foregut/primordial pharynx, inferior to 4th pharyngeal arch
Primordium of tracheobronchial tree develops where
Caudal to 4th pharyngeal pouch
Endoderm of laryngotracheal groove gives rise to
Pulmonary epithelium and glands of larynx, trachea and bronchi
Splanchnic mesoderm (from lateral plate) gives rise to
CT, cartilage, and smooth muscle in larynx, trachea and bronchi
Surrounds foregut
Laryngotracheal groove will evaginate to form
Laryngotracheal diverticulum (lung bud)
What gives rise to the respiratory bud
The diverticulum elongates and the distal end enlarges to form the globular respiratory bud
How is the trachea and esophagus separated
Tracheoesophageal folds fuse and form the tracheoesophageal septum at 5 weeks
Dorsal portion of foregut forms
Primordium of oropharynx, esophagus
Ventral part of foregut forms
Laryngotracheal tube (primordium of larynx, trachea, bronchi and lungs
Epithelial lining of larynx comes from
Endoderm of laryngotracheal tube
Cartilages of larynx come from
Mesenchyme of 4th/6th pharyngeal arches (NCC derived)
Arytenoid swellings arise from
Mesenchyme
Epiglottis develops from
Hypopharyngeal eminence, produced by mesenchyme of 3/4th pharyngeal arches
Recanalization of larynx
Laryngeal epithelium proliferates and occludes laryngeal lumen by the 10th week
Laryngeal atresia
Failure of recanalization of the larynx
Obstruction of the upper fetal airway (CHAOS- congenital high airway obstruction syndrome)
Airways become dilated, lungs are enlarged and filled with fluid
Diaphragm flattened or inverted, and there is fetal ascites and/or hydrops
Tracheal development
Laryngeotracheal diverticulum forms trachea and primary bronchial buds
Endoderm differentiates into tracheal epithelium and glands, and pulmonary epithelium
Splanchnic mesoderm forms tracheal cartilages, CT and muscle
Tracheoesophageal fistula
Abnormal connection b/w trachea and esophagus
Many cases are associated with esophageal atresia, blind esophagus
Failure of foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo
Tracheoesophageal fistula symptoms
Cannot swallow, frequently drool saliva, immediate regurgitation when fed
Polyhydramnios- excess amniotic fluid
-cannot enter the stomach/intestines for absorption
-not transferred for disposal via the placenta
Respiratory buds form when and from what
Form during 4th week from enlargement of the distal end of the laryngotracheal diverticulum
What regulates the branching pattern of the lung endoderm
Splanchnic mesenchyme
Primary bronchial buds and bronchopulmonary segments form when
Primary- week 5
BP segments- week 7
Lungs later acquire a layer of
Visceral pleura (from splanchnic portion of lateral plate mesenchyme)
Thoracic body wall becomes lined by a layer of
Parietal pleura (somatic portion of lateral plate mesoderm)
Psuedoglandular stage of lung maturation
Weeks 5-17
Looks like exocrine glands
All major elements of the lung have formed, except those involved with gas exchange
Fetus cannot survive
Canalicular stage of lung maturation
16-25 weeks Overlaps pseudoglandular Vascularization Respiratory bronchioles Primordial alveolar & sacs present (primitive alveoli) May be able to survive
Terminal sac stage of lung maturation
24 weeks-birth
Numerous alveoli form
Thin epithelium w/increased vascularization
Type 1/2 pneumocytes (type 2 are surfactant producing)
Lymphatic capillaries
Gas exchange can occur, survivable
Alveolar stage of lung maturation
32wks-8years Alveolocapillary membrane Primitive alveoli Form more primitive alveoli 95% of alveoli develop postnatally Mature alveoli may form until ~8 years
Splanchnic mesoderm importance in bronchi development
Critical for formation of:
Cartilaginous plates
Bronchial smooth muscle and CT
Pulmonary CT and capillaries
Fetal breathing movements
Required for normal lung development
Conditions respiratory muscles
Aeration of lungs requires rapid replacement of intra-alveolar fluid with air
Pulmonary agenesis
Unilateral- complete absence of a lung or a lobe and accompanying bronchi
Respiratory bud fails to split into R/L bronchial buds
Oligohydramnios
Insufficient amniotic fluid production
Typically associated with renal agenesis or failure
Severe and chronic oligohydramnios retards lung development
Pulmonary hypoplasia
Restriction of fetal thorax (from uterine pressure)
Decreased hydraulic pressure on lungs
Affects stretch receptors and lung growth
Risk increases significantly with oligohydramnios <26 weeks
Respiratory distress syndrome
Rapid, labored breathing shortly after birth
Significant cause of death in premature infants
Surfactant deficiency is a major cause:
-lungs are underinflated
-alveoli contain fluid that resembles glassy membrane
-irreversible changes in type II alveolar cells so they cant produce surfactant
Signs/symptoms of RDS
Tachypnea, nasal flaring
Suprasternal, intercostal or subcostal retractions
Grunting and cyanosis
Congenital lung cysts
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 or difficulty breathing
