Respiratory Embryology Flashcards
The respiratory system begins as a median outgrowth known as:
Laryngotracheal groove
Where is the laryngotracheal groove located?
The floor of the caudal end of the foregot/primordial pharynx and inferior to the 4th pharyngeal arches.
Tracheobronchial tree develops…
Caudal to the 4th pharyngeal arches.
Endoderm of laryngotracheal groove gives rise to:
Pulmonary epithelium, glands of pharynx, trachea, and bronchi.
Splanchnic layer of lateral plate mesoderm gives rise to:
CT, cartilage, smooth muscle surrounding foregut.
Laryngotracheal groove envaginates to form:
Laryngotracheal diverticulum (lung bud), which forms trachea and primary bronchial buds (2).
Development of the lower respiratory system from endoderm
The diverticulum elongates and becomes invested in splanchnic mesenchyme.
The distal end enlarges to form respiratory bud (origin of respiratory tree).
Tracheoesophageal folds
Fuse to form the tracheoesophageal septum.
Separates the esophagus and trachea.
Occurs end of week 5.
Epithelial lining of the larynx is from:
Cartilage of the larynx is from:
Endoderm of laryngotracheal tube.
Mesenchyme of 4th and 6th pairs of pharyngeal arches (neural crest derived).
Role of mesenchyme in development of the pharynx
Produces paired arytenoid swellings.
Converts the primordial glottis into T-shaped laryngeal inlet.
Role of laryngeal epithelium in development of the larynx
It proliferates and occludes lumen of larynx.
Becomes recanalized in week 10 (forms the vocal folds/cords and vestibular folds at that time).
Epiglottis develops from:
Hypopharyngeal eminence, which is produced from mesenchyme of 3-4th PAs.
Laryngeal muscles develop from:
Myoblasts of 4th and 6th PAs.
Laryngeal atresia
Birth defect resulting from a failure of recanalization of the larynx.
Causes obstruction of the upper airway, causing dilation of the airways and lung enlargement.
Diaphragm can become inverted.
Treatment in endoscopic dilation of the laryngeal web.
Tracheoesophageal fistula
Abnormal connection between trachea and esophagus.
most common abnormality of LRT.
Commonly associated with esophageal atresia.
From failure of foregut endoderm to proliferate quickly enough in comparison to the rest of the embryo.
Pt cannot swallow, drools frequently, regurgitates when fed. Reflux can occur.
Polyhydramnios
Polyhydramnios
Excess amniotic fluid.
Cannot enter the stomach/intestines for absorption.
Where do the primary lung buds grow?
Into the Pericardioperitoneal canals.
Primary bronchial buds branch in the ____ week and form secondary and tertiary bronchial buds.
5th
Pattern of bronchi development (5 steps)
Main bronchi -> secondary bronchi -> lobar -> segmental -> intrasegmental branches.
Stages of lung development (4)
Pseudoglandular (5-17 wks)
Canalicular (16-25 wks)
Terminal sac (24 wks-birth)
Alveolar (32 wks-8 yrs)
Pseudoglandular stage
5 - 17 wks
Look like exocrine glands.
All major elements of lung have formed, except tose involved in gas exchange.
Fetus cannot survive.
Canalicular stage
16 - 25 wks Overlaps w/ pseudoglandular. Vascularization occurs. Respiratory bronchioles form. Primitive alveoli form. Possible survival.
Terminal sac stage
24 wks - birth Numerous alveoli form. Thin epithelium w/ increased vascularization. Type I/II pneumocytes form. Lymphatic capillaries form. Gas exchange occurs. Survival.
Alveolar stage
32 wks - 8 yrs
Alveolocapillary membrane forms.
Primitive alveoli become mature alveoli.
About 95% of mature alveoli occur postnatally.
In the lungs, splanchnic mesoderm gives rise to:
Cartilaginous plates
Bronchial smooth muscle and CT
Pulmonary CT and capillaries
Fetal breathing movements (FBMs)
Needed for normal lung development.
“Trains” respiratory muscles.
Used as a predictor of fetal outcome.
Needs to be forceful enough to case aspiration of amniotic fluid to stimulate lung development.
FBMs cleared via (3):
Mouth/nose by pressure on the fetal thorax during vaginal delivery.
Pulmonary vasculature
Lymphatics
Pulmonary agenesis
Complete absence of a lung or lobe and accompanying bronchi.
Respiratory bud fails to split.
Oligohydramnios
Insufficient amniotic fluid production.
Severe or chronic oligohydramnios retards lung development.
Pulmonary hypoplasia
Restriction of fetal thorax from uterine pressure.
Decreases hydraulic pressure on lungs.
Affects stretch receptors and lung growth.
Risks increase if coupled with oligohydramnios.
Respiratory distress syndrome
Rapid, labored breathing develops shortly after birth.
Surfactant deficiency is major cause of RDS (irreversable damage to type II pneumocytes)
Sx: tachypnea, nasal flaring, costal abnormalities, grunting, cyanosis.
Congenital lung cysts
Filled with fluid or air.
Thought to be formed by dilation of terminal bronchi.
May exhibit wheezing, cyanosis, difficulty breathing.
