Lecture 18: The respiratory system: embryology Flashcards
Components of upper respiratory tract
nasal and oral cavities
Components of lower respiratory tract
larynx, trachea, bronchii, and lungs
When and where do the laryngotracheal grooves form
Week 4, median outgrowth of caudal end of the ventral wall of the pharynx (inferior to the fourth pharyngeal pouch)
When and where does the long bud form
End of week 4, ventral to the caudal part of the fore-gut
Laryngotracheal tube
Eventually elongates from the long bud –>tracheal bud –> laryngotracheal tube. Becomes divested from the pharynx, but still attached through primordial laryngeal outlet. Becomes invested with splanchnic mesoderm
Primordial laryngeal outlet
The remaining opening between the laryngotracheal tube and the rest of the pharynx (what becomes the esophagus)
tracheoesophageal (TE) septum
Creates the increased separation between the laryngotracheal tube and the esophagus
endoderm of laryngotracheal tube gives rise to
epithelium and glands of larynx, trachea, bronchii, and pulmonary epithelium
splanchnic mesoderm covering of laryngotracheal tube gives rise to
connective tissue, cartilage and smooth muscle
Larynx function
swallowing, respiration, voice production
upper border of the larynx
epiglottis (mouth)
lower border of the larynx
cricoid cartilage (trachea)
arytenoid swellings
Initial growths of larynx, mesenchyme grows up from cranial end of laryngotracheal tube, are the lateral borders of the laryngeal inlet. Meet the bottom of the epiglottis
laryngeal inlet
t-shaped slit between arytenoid swellings and below the epiglottis, primordial glottis
epiglottis
Develops from the hypobranchial eminence. Muscles cells develop from myoblasts in 4-6 arches, innervated by laryngeal branches of the vagus nerve that supply those arches.
Recanalization of larynx
During proliferation of mesenchyme the larynx lumen gets occluded, usually recanalized during week 10
Laryngeal Ventricles
During recanalization, recesses form in walls of larynx called ventricles. The recesses are bounded by folds of tissue that become vocal cords
epithelial lining of larynx develops from
endothelial lining of the endoderm of the laryngotracheal tube
cartilage of the larynx develops from
4th and 6th pharyngeal arches mesenchyme, that originated from neural crest cells
laryngeal web
incomplete recanalization, web forms at the level of the vocal cord, partial obstruction of newborn’s breathing
primordium of trachea
straight part of laryngotracheal tube (also called the respiratory diverticulum)
primordium of lung/bronchi
bud part of the laryngotracheal tube (also called the respiratory diverticulum)
what controls the difference in branching between trachea and lung/bronchii
the mesoderm covering the straight part of laryngotracheal tube –> inhibits branching
the mesoderm covering the bud part –> promotes budding
tracheo-esophageal folds
fuse to form TE septum
T-E fistula
abnormal communication between trachea and esophagus, caused by incomplete fusion of TE folds, 85% of the time ends in esophageal atresia (esophagus ends in a pouch); most common anomaly of the lower respiratory tract, more common in males than females
Esophageal atresia
The top part of esophagus ends in pouch, bottom of esophagus joins the trachea
Purpose of lungs/bronchii
Site of gas exchange
bronchial buds
The lung bud divides into two out-pouchings called bronchial buds at the beginning of week 5
Pre-cursor of visceral pleura
Visceral pleura is closely associated with the surface of the lung, rises from the splanchnic mesoderm
Pre-cursor of the parietal pleura
Thick layer that overlays the visceral pleura, with the pleural cavity in the middle. arises from the somatic mesoderm
right bronchial bud vs. left bronchial bud
right bronchial bud is more vertical and larger (3 secondary buds) than left bud (2 secondary buds). Right bud has three lobes. Patient’s right, my left.
secondary branching of bronchi,
3 on right, 2 on left, order after right left branching, create lobes. at 7 weeks
segmental/tertiary branching
10 in right lung, 8-9 at left lung around 7 weeks
pseudo-glandular period
5-17 weeks of development, no space within lungs to diffuse oxygen within tissue, looks like gland tissue, infant cannot survive.
Formation and growth of duct systems, bronchii not well developed
canalicular period
16-25 weeks, late canalicular period you can survive (some respiration possible)
Formation and growth of bronchii system, vascularization very developed, alveolar sacs not well developed
terminal sac period
24 weeks-birth
epithelium v. thin, the capillaries are v. close to the bronchioles, true gas exchange possible
alveolar period
birth/32 weeks-8 years. the alveoli ( and type I alveoli cells) expand and multiply to increase surface area, as does the capillary network,
type II alveolar cells create surfactant
Creation of 2 parallel circulation systems (respiratory and systemic)
Respiratory Distress syndrom
Born before 26-28 weeks, caused by lack of surfactant which helps alveoli inflated under low pressure –> creates inadequate gas exchange. Also caused by lack of capillary vasculature, lack of lung development
terminal saccules
primordial alveolar sacs
one cause of asthma
smooth muscles surrounding bronchii (originating from mesenchyme) go into spasm
lung development after birth?
the air:blood surface area increases exponentially by increases in alveoli and capillaries (50 mill. @ birth –> 300 mill. @ year 8)
chest x-ray of infant compared to adult
Infant’s chest has more fluid and fewer alveoli than adults, appears dense and dark
fetal breathing movement
conditions respiratory movements, stimulates lung/diaphragm developments, even though lungs are filled with fluid
Factors necessary for fetal lung development
fetal breathing movement, adequate space in the thorax, amniotic fluid volume (bc that keeps the muscles of the uterus expanded, allowing the lungs to have space to grow)
Treatments for respiratory distress syndrome
Caused by pre-mature birth, lack of surfactant production. Give steriods (betamethasone) to the mom if she’s about to go into pre-term labor which helps the fetus manufacture surfactant before birth , can also give the pre-me baby manufactured surfactant.
