Lecture 18: The respiratory system: embryology

Question 1

Components of upper respiratory tract

Answer 1

nasal and oral cavities

Question 2

Components of lower respiratory tract

Answer 2

larynx, trachea, bronchii, and lungs

Question 3

When and where do the laryngotracheal grooves form

Answer 3

Week 4, median outgrowth of caudal end of the ventral wall of the pharynx (inferior to the fourth pharyngeal pouch)

Question 4

When and where does the long bud form

Answer 4

End of week 4, ventral to the caudal part of the fore-gut

Question 5

Laryngotracheal tube

Answer 5

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

Question 6

Primordial laryngeal outlet

Answer 6

The remaining opening between the laryngotracheal tube and the rest of the pharynx (what becomes the esophagus)

Question 7

tracheoesophageal (TE) septum

Answer 7

Creates the increased separation between the laryngotracheal tube and the esophagus

Question 8

endoderm of laryngotracheal tube gives rise to

Answer 8

epithelium and glands of larynx, trachea, bronchii, and pulmonary epithelium

Question 9

splanchnic mesoderm covering of laryngotracheal tube gives rise to

Answer 9

connective tissue, cartilage and smooth muscle

Question 10

Larynx function

Answer 10

swallowing, respiration, voice production

Question 11

upper border of the larynx

Answer 11

epiglottis (mouth)

Question 12

lower border of the larynx

Answer 12

cricoid cartilage (trachea)

Question 13

arytenoid swellings

Answer 13

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

Question 14

laryngeal inlet

Answer 14

t-shaped slit between arytenoid swellings and below the epiglottis, primordial glottis

Question 15

epiglottis

Answer 15

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.

Question 16

Recanalization of larynx

Answer 16

During proliferation of mesenchyme the larynx lumen gets occluded, usually recanalized during week 10

Question 17

Laryngeal Ventricles

Answer 17

During recanalization, recesses form in walls of larynx called ventricles. The recesses are bounded by folds of tissue that become vocal cords

Question 18

epithelial lining of larynx develops from

Answer 18

endothelial lining of the endoderm of the laryngotracheal tube

Question 19

cartilage of the larynx develops from

Answer 19

4th and 6th pharyngeal arches mesenchyme, that originated from neural crest cells

Question 20

laryngeal web

Answer 20

incomplete recanalization, web forms at the level of the vocal cord, partial obstruction of newborn’s breathing

Question 21

primordium of trachea

Answer 21

straight part of laryngotracheal tube (also called the respiratory diverticulum)

Question 22

primordium of lung/bronchi

Answer 22

bud part of the laryngotracheal tube (also called the respiratory diverticulum)

Question 23

what controls the difference in branching between trachea and lung/bronchii

Answer 23

the mesoderm covering the straight part of laryngotracheal tube –> inhibits branching
the mesoderm covering the bud part –> promotes budding

Question 24

tracheo-esophageal folds

Answer 24

fuse to form TE septum

Question 25

T-E fistula

Answer 25

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

Question 26

Esophageal atresia

Answer 26

The top part of esophagus ends in pouch, bottom of esophagus joins the trachea

Question 27

Purpose of lungs/bronchii

Answer 27

Site of gas exchange

Question 28

bronchial buds

Answer 28

The lung bud divides into two out-pouchings called bronchial buds at the beginning of week 5

Question 29

Pre-cursor of visceral pleura

Answer 29

Visceral pleura is closely associated with the surface of the lung, rises from the splanchnic mesoderm

Question 30

Pre-cursor of the parietal pleura

Answer 30

Thick layer that overlays the visceral pleura, with the pleural cavity in the middle. arises from the somatic mesoderm

Question 31

right bronchial bud vs. left bronchial bud

Answer 31

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.

Question 32

secondary branching of bronchi,

Answer 32

3 on right, 2 on left, order after right left branching, create lobes. at 7 weeks

Question 33

segmental/tertiary branching

Answer 33

10 in right lung, 8-9 at left lung around 7 weeks

Question 34

pseudo-glandular period

Answer 34

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

Question 35

canalicular period

Answer 35

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

Question 36

terminal sac period

Answer 36

24 weeks-birth

epithelium v. thin, the capillaries are v. close to the bronchioles, true gas exchange possible

Question 37

alveolar period

Answer 37

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)

Question 38

Respiratory Distress syndrom

Answer 38

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

Question 39

terminal saccules

Answer 39

primordial alveolar sacs

Question 40

one cause of asthma

Answer 40

smooth muscles surrounding bronchii (originating from mesenchyme) go into spasm

Question 41

lung development after birth?

Answer 41

the air:blood surface area increases exponentially by increases in alveoli and capillaries (50 mill. @ birth –> 300 mill. @ year 8)

Question 42

chest x-ray of infant compared to adult

Answer 42

Infant’s chest has more fluid and fewer alveoli than adults, appears dense and dark

Question 43

fetal breathing movement

Answer 43

conditions respiratory movements, stimulates lung/diaphragm developments, even though lungs are filled with fluid

Question 44

Factors necessary for fetal lung development

Answer 44

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)

Question 45

Treatments for respiratory distress syndrome

Answer 45

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.