Lecture 18: The respiratory system: embryology Flashcards Preview

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Flashcards in Lecture 18: The respiratory system: embryology Deck (45):

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



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.