Pediatrics: Respiratory Embryology

Question 1

Respiratory Diverticulum

Answer 1

duringt the 4th week the foregut endoderm evaginates ventrally at the level of the 4th pharyngal pouch

Question 2

what connectsthe respiratoy diverticulum to the pharyngeal cavity

Answer 2

laryngotracheal orifice

Question 3

formation of the lung bud

Answer 3

occurs due to the elonatuin of the respiratory diverticulum and the expansion of the distal end.

Question 4

formation of the primary bronchi

Answer 4

occurs due to bifurcation of the lung bud

Question 5

tracheoesophageal folds

Answer 5

alters the connection of the lung bud to the forgut- paired lateral indentations that grow towards midline

Question 6

tracheoesophagel septum

Answer 6

fusion of the tracheoesophageal folds at midline- separates the ventral tracea form the more dorsal esophagus

Question 7

laryngotracheal groove

Answer 7

portal within the incomplete tracheoesophageal septum that links the tacheal lumen to the pharyngeal lumen

Question 8

what controls the development of the lower repsiratory tracts

Answer 8

2 opposing gradiens - dorsal/ventral SOX2 (stronger more dorsal = likely to be disgestive ventral/dorsal NKX2 (stronger more ventrally = respiratory) and Barx1 = formation of tracheoesophogeal folds/septum (i.e the separation of the trachea and the esophagus)

Question 9

what gene controls the separation of the trachea and esophagus

Answer 9

Barx1

Question 10

Tracheoesophageal fisula

Answer 10

failure of the junction between the trachea and the esophagus to form. 1 in every 4,000 births and more common in males. Result in excessive salvation and regurgitation, large air bubbles in the GI tract, and food being regurgitated into the respiratory tract . Placement of NG tube is impossible

Question 11

esophageal atresia

Answer 11

esophagous terminates in a blind ending pouch

Question 12

embryonic origins of the larynx

Answer 12

laryngeal cartilage and muscles develop form the mesoderm of the 4th and 6th arches in weeks 4-10 (smaller laryngeal cartilages do not develop until end of fetal period)

Question 13

Hypopharyngeal eminence

Answer 13

forms from the 3rd and 4th pharyngeal arches- caual portion forms the epiglottis and separate mesenchymal condensations form the arytenoid swelling

Question 14

arytenoid swelling

Answer 14

forms arytenoid cartilage and rehapes the laryngotracheal groove into the glottis

Question 15

innervation of the 4th and 6th pharyngeal arches

Answer 15

vagus nerve

Question 16

explain the development of dual innervation of the adult larynx

Answer 16

larynx develops from pharyngeal arches 4 and 6 - 4 is innervated by recurrent laryngeal nerve and 6 is innervated by superior laryngeal nerve

Question 17

maturational changes in the larynx

Answer 17

position of the larynx is initally more superior to facilitate suckling and then moves to C4-7 form years 2-6.

Question 18

laryngeal epithelium is dervied from what structure

Answer 18

foregut - weeks 8-9 the proliferating epithelium occludes the glottis - wk 10 the epithelium regresses leaving the glottal opening supperiorly and the ventricles and folds of the larynx laterally

Question 19

Laryngeal atresia

Answer 19

failure of the epithelium to clear the glottal opening - babies boren with largyngal atresial will be unable to cry or ventilate and requires immediate tracheostomy

Question 20

laryngeal web

Answer 20

partial laryngeal atresia that typically presents as disphonic (low umbling cry) with a range of airway obstruction

Question 21

Intraembryonic (Coelomic) Cavity

Answer 21

forms as a slit between splanchnic and somatoc lateral plate mesoderm. Slit expands as lateral plate extends ventrally to encompass the yolk sac

Question 22

tranverse septum

Answer 22

as the embryo curls during early development the inferior surface of the developing heart abuts the outer surface of the viteline sac and the mesenchyme in this area thickens to form the transverse septum (heart develops immediately superior to transverse septum and the liver develops inferior to the transverse septum

Question 23

innervation of the transverse septum

Answer 23

phrenic nerve- gets pulled caudally along with the septum in development and results in the great length of the nerve

Question 24

what does the transverse septum form

Answer 24

central tendon of the diaphragm (weeks 4-7)

Question 25

how far does the transverse septum extend

Answer 25

only extends to the ventral surface of foregut

Question 26

the foregut is suspended in the ceolomic cavity by what structure

Answer 26

dorsal mesentary

Question 27

pleuroperitoneal canals

Answer 27

after the transverse septu, partitons the ventral protion of the ceolomic cavity the dorsal ortion remains continuous on either side of the foregut. Paired dorsal connection = pleuroperitoneal canals

Question 28

formation of the diaphragm

Answer 28

peritoneal folds form the dorsolateral margin of the the pleuroperitoneal cnals and grow towards the dorsal free edge of the transverse septum. The folds expand into the pleuroperitoneal membranes which fuse with the transverse septum to effectively partition the pleuroperitoneal canals - fusions typically occurs in the 6th week

Question 29

what forms the central tendon of the diaphragm

Answer 29

Tranverse septum+ Pleuroperitoneal Membranes

Question 30

what forms the crura of the diaphragm

Answer 30

dorsal mesentary of the esophagus

Question 31

what forms the peripheral muscle of the diaphragm

Answer 31

peripheral muscles of the transverse septum and pleuroperitoneal membranes

Question 32

congenital diaphragmatic hernia

Answer 32

failure of one of the pleuroperitoneal membranes to form and/or fuse with the transverse septum. More common on the left- results in perioneal viscera expanding into thorax and physically blocking the development of the lung (pulmonary hypoplasia) - generally life threatening

Question 33

Subdivision of the thoraic cavity

Answer 33

Pleuropericardial folds (membranes) develop parallel but superior to the pleuoperitoneal membranes. As the folds extend from the body wall they carry paired phrenic nerve and common cardinal vein. Pleuropericardial membranes meed midline and separate the pleural cavity form the ventral pericardial cavity

Question 34

fibrous pericardium is derived from what

Answer 34

pleuropericardial membrane

Question 35

what signals the early branching the the bronchial tree

Answer 35

the mesoderm lining of the MEDIAL side of the pleuroperitoneal canal/pleural cavity - releases messenger compounds (FGF-10, Wnt7b, bmp4, shh) that induce the expansion and division of the bronchial tree

Question 36

when do primary bronchi (bronchial buds) form

Answer 36

W5 - the right bronchus is larger in diameter and more vertical then the left -this is where we first start to see asymmetry

Question 37

when do the secondary bronchi form

Answer 37

W7- 3 on the right 2 on the left

Question 38

when do the tertiary bronchi form

Answer 38

W8- 10 on the right 9 on the left

Question 39

congenital bronchogenic cysts

Answer 39

due to abnormal bronchial tree branching - most common on the mediastinal surface but can be intralobular. Initially fluid filled but become air filled over time. Occurs in 1 in 30,000 births. Tends to lead to lobular pulmonary hypoplasia

Question 40

name the four stages of lung development

Answer 40

1.) Pseudoglandular phase (W6-16) 2.) Canalicular Phase (W16-26) 3.) Terminal Sac Phase (W26-birth) 4.) Alveolar period (W32-8 years)

Question 41

Pseudoglandular phase

Answer 41

W6-16-lung resembles and exocrine gland- terminate in terminl bronchioles lined with simple columnar epithelium, modest vascularity with no interation between capillaries and terminal bronchioles = no respiration occurs in this phase

Question 42

Canalicular phase

Answer 42

W16-26. Terminal bronchioles give rise to respiratory bronchioles which give rise to alveolar ducts . Epithelium becomes simple cuboidal. Increase in capillary density and capillaries abut alveolar ducts. Limited respiration possible by the end of this phase

Question 43

Terminal Sac Phase

Answer 43

W26-Birth. Terminal sacs expand off alveolar ducts. Epithelium shifts to simple squamous and thre is differentiation into type I pneumocytes (forms blood air barrier) and type II pneumocutes (produce surfactant)

Question 44

Alveolar period

Answer 44

W32-8 years. Secondary septa partition the terminal sacs into alveoli. During this process the number of alveoli will increase from ~30 million to ~300 million

Question 45

what accounts for the increase in size between newborn and adult lung

Answer 45

formation of more respiratory bronchioles NOT alveoli

Question 46

Repiratory Distress Syndrome

Answer 46

leading cause of death among premature infants. Caused by failure of type II pneumocytes to produce adequate amounts of surfactant leading to collapse and reducing the sirface area available for respiration. Bell shaped thorax on radiograph and ground glass (reticulohranularity) appearance in the lungs

Question 47

Hitological trademark of Respiratory Distress Syndrome

Answer 47

Acinar Atelectass (collapse of the alveoli and alveolardicts), dilation of the terminal bronchioles, deposition of an eosinophilic membrane (made of fibrin and necrotic cells) on the inner surface of the terminal parts of the bronchiole tree)

Question 48

Pulmonary Hypoplasia

Answer 48

marked reduction in the size of the lungs - frequent in stillborns. May result from defect in the lung themselves (primary) or from secondary influences (oligohydraminos or congenital diaphragmatic hernia)