Embryology 5 Flashcards
Broadly speaking, the respiratory system is derived from what embryologic structure?
foregut
What are the three primary structures of the upper respiratory system?
nose
nasopharynx
oropharynx
Though the respiratory system in general arises from the foregut, the upper respiratory system specifically arises from
the primitive pharynx
What are the four primary structures of the lower respiratory system?
larynx
trachea
bronchi
lungs
The lower respiratory system develops from
the laryngotracheal groove, an outgrowth of the primitive pharynx
Describe the location of the laryngotracheal groove.
laryngotracheal groove lies caudally to the 4th pair of pharyngeal pouches
The epithelium and glands of the lower respiratory system are derived from
the endoderm that lines laryngotracheal groove
The endoderm of the laryngotracheal groove gives rise to
the epithelium and glands found in the lower respiratory tract
Cartilage, connective tissue, and smooth muscle of the lower respiratory system are derived from
the visceral lateral mesoderm that surrounds the foregut
The visceral lateral mesoderm of the foregut gives rise to (3)
cartilage
connective tissue
smooth muscle
[all of the lower respiratory system]
Describe the fate of the laryngotracheal groove.
laryngotracheal groove → laryngotracheal diverticulum → elongation to become laryngotracheal tube
What is the location of the laryngotracheal diverticulum?
located ventrally to the foregut
Describe how the primitive pharynx further develops during week 5. (2)
lateral walls of primitive pharynx develop folds called tracheoesophageal folds, which fuse by the end of week 5
ventral laryngotracheal tube is therefore separated from dorsal esophageal tube
What is the primordial laryngeal inlet? (2)
the cranial-facing junction of the laryngotracheal tube and esophagus formed during week 5
primordial laryngeal inlet will eventually give rise to larynx
What is the tracheoesophageal septum?
the structure that separates the dorsal esophagus from the ventral laryngotracheal tube
What causes tracheoesophageal fistulas?
faulty separation of trachea and esophagus
Describe the most common manifestation of tracheoesophageal fistulas.
superior part of esophagus ends blind (esophageal atresia), which means that food cannot reach the stomach
Describe the milder manifestation of tracheoesophageal fistulas.
patency of trachea and esophagus is preserved, but connections between the 2 tubes cause aspiration of esophageal contents into lungs
The epithelium of the larynx develops from
the endoderm of the cranial portion of the laryngotracheal tube
Laryngeal cartilages develop from
cartilage portions of pharyngeal arches 4 and 6
[note: does not include epiglottis]
The epiglottis develops from
caudal portion of hypobranchial eminence
The cranial part of the hypobranchial eminence contributes to
the tongue
The laryngeal muscles are derived from
pharyngeal arches 4 and 6
The laryngeal muscles are innervated by
laryngeal branches of the vagus nerve (CN X)
What gives rise to the respiratory epithelium of the trachea?
endoderm of caudal portion of laryngotracheal tube
The endoderm of caudal portion of laryngotracheal tube differentiates into
the respiratory epithelium of the trachea
The cartilage, connective tissue, and smooth muscle of the trachea are derived from
the visceral lateral mesoderm that surrounds the endoderm of the laryngotracheal tube
The visceral lateral mesoderm that surrounds the endoderm of the laryngotracheal tube gives rise to
the cartilage, connective tissue, and smooth muscle of the trachea
Where in the lungs does gas exchange take place?
alveoli
Alveoli are derived from
the epithelium of the lung
List the pathway from the trachea to the alveoli.
trachea → bronchial tree ( → bronchi → bronchioles → respiratory bronchioles) → alveoli
Describe the pathway of lung development.
branching of respiratory buds into 2 bronchial buds
bronchial buds expand into pericardioperitoneal cavities
in week 5, bronchial buds have formed 2 primary bronchi
Differentiate between the right and left bronchus.
right bronchus is more vertically oriented
By week 5, the two primary bronchi have formed. How do they develop further?
primary bronchi branch into lobar (secondary) bronchi [3 on right, 2 on left] and then further into segmental (tertiary) bronchi [10 on right, 8-9 on left]
Why do aspirated foreign objects tend to lodge in the right bronchus?
because it is more vertically oriented
What is the significance of week 26 in embryological lung development?
specialized lung cells start to produce surfactant
What is the function of surfactant in the lungs? (2)
reduces surface tension of alveoli
essential for efficient gas exchange
Babies born prematurely, but after 26 weeks of gestation, may experience
respiratory distress syndrome, because surfactant production has not reached maximum
What is a treatment option for babies in respiratory distress due to premature birth and therefore inadequate surfactant production?
corticosteroids
(T/F) Lung maturation continues into childhood.
True. New alveoli are added until ~8 years of age.
The embryological formation of the bronchial tree is typically considered complete at what point of time?
by week 24 (at which point, 17 orders of branching have occurred)
What is lung hypoplasia?
poorly developed bronchial tree
What is the result of lung hypoplasia?
diminished vital capacity
What are the symptoms of lung hypoplasia?
tachypnea (rapid breathing)
respiratory distress under stressful conditions (i.e. exercise)
What is the cause of lung hypoplasia? (2)
compression of developing lungs, due to:
(1) decreased amniotic fluid
(2) diaphragmatic hernia
