Pediatrics: Respiratory Embryology Flashcards
Respiratory Diverticulum
duringt the 4th week the foregut endoderm evaginates ventrally at the level of the 4th pharyngal pouch
what connectsthe respiratoy diverticulum to the pharyngeal cavity
laryngotracheal orifice
formation of the lung bud
occurs due to the elonatuin of the respiratory diverticulum and the expansion of the distal end.
formation of the primary bronchi
occurs due to bifurcation of the lung bud
tracheoesophageal folds
alters the connection of the lung bud to the forgut- paired lateral indentations that grow towards midline
tracheoesophagel septum
fusion of the tracheoesophageal folds at midline- separates the ventral tracea form the more dorsal esophagus
laryngotracheal groove
portal within the incomplete tracheoesophageal septum that links the tacheal lumen to the pharyngeal lumen
what controls the development of the lower repsiratory tracts
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)
what gene controls the separation of the trachea and esophagus
Barx1
Tracheoesophageal fisula
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
esophageal atresia
esophagous terminates in a blind ending pouch
embryonic origins of the larynx
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)
Hypopharyngeal eminence
forms from the 3rd and 4th pharyngeal arches- caual portion forms the epiglottis and separate mesenchymal condensations form the arytenoid swelling
arytenoid swelling
forms arytenoid cartilage and rehapes the laryngotracheal groove into the glottis
innervation of the 4th and 6th pharyngeal arches
vagus nerve
explain the development of dual innervation of the adult larynx
larynx develops from pharyngeal arches 4 and 6 - 4 is innervated by recurrent laryngeal nerve and 6 is innervated by superior laryngeal nerve
maturational changes in the larynx
position of the larynx is initally more superior to facilitate suckling and then moves to C4-7 form years 2-6.
laryngeal epithelium is dervied from what structure
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
Laryngeal atresia
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
laryngeal web
partial laryngeal atresia that typically presents as disphonic (low umbling cry) with a range of airway obstruction
Intraembryonic (Coelomic) Cavity
forms as a slit between splanchnic and somatoc lateral plate mesoderm. Slit expands as lateral plate extends ventrally to encompass the yolk sac
tranverse septum
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
innervation of the transverse septum
phrenic nerve- gets pulled caudally along with the septum in development and results in the great length of the nerve
what does the transverse septum form
central tendon of the diaphragm (weeks 4-7)
how far does the transverse septum extend
only extends to the ventral surface of foregut
the foregut is suspended in the ceolomic cavity by what structure
dorsal mesentary
pleuroperitoneal canals
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
formation of the diaphragm
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
what forms the central tendon of the diaphragm
Tranverse septum+ Pleuroperitoneal Membranes
what forms the crura of the diaphragm
dorsal mesentary of the esophagus
what forms the peripheral muscle of the diaphragm
peripheral muscles of the transverse septum and pleuroperitoneal membranes
congenital diaphragmatic hernia
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
Subdivision of the thoraic cavity
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
fibrous pericardium is derived from what
pleuropericardial membrane
what signals the early branching the the bronchial tree
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
when do primary bronchi (bronchial buds) form
W5 - the right bronchus is larger in diameter and more vertical then the left -this is where we first start to see asymmetry
when do the secondary bronchi form
W7- 3 on the right 2 on the left
when do the tertiary bronchi form
W8- 10 on the right 9 on the left
congenital bronchogenic cysts
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
name the four stages of lung development
1.) Pseudoglandular phase (W6-16) 2.) Canalicular Phase (W16-26) 3.) Terminal Sac Phase (W26-birth) 4.) Alveolar period (W32-8 years)
Pseudoglandular phase
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
Canalicular phase
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
Terminal Sac Phase
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)
Alveolar period
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
what accounts for the increase in size between newborn and adult lung
formation of more respiratory bronchioles NOT alveoli
Repiratory Distress Syndrome
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
Hitological trademark of Respiratory Distress Syndrome
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)
Pulmonary Hypoplasia
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)
