Development of the Respiratory System Flashcards

1
Q

What germ layer forms the respiratory system

A
  • The endoderm
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2
Q

the larynx & trachea are developed in the ___________ of development

A
  • 4th week
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3
Q

Where does the laryngotracheal groove appear

A
  • At the caudal end on the ventral wall of the primitive pharynx
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4
Q

Explain the development of the trachea

A
  • Endodermal lining of laryngotracheal tube → tracheal & pulmonary epithelium & glands (Wnt2/2b, FGF10, BMP4)
  • Splanchnic mesenchyme around the LT tube → cartilage, connective tissue & muscles of the trachea
  • LT groove → LT diverticulum → LT tube
  • Tracheoesophageal septum separates the LT tube from the pharynx (now esophagus)
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5
Q

What does the tracheoesophageal septum do?

A
  • It divides the cranial part of the fore gut into the ventral respiratory passageways (NKX2.1,Shh, Wnt7b) and the dorsal digestive passageways (SOX2, BMP7) with BARX1 at the septum
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6
Q

Explain the development of the bronchi

A
  • A respiratory bud appears at the caudal end of the laryngotracheal diverticulum in the 4th week of development
  • The bud divides = 2 primary bronchial buds which then grow laterally → L&R primary bronchi → 2L&3R secondary bronchi → 8-9L&10R tertiary bronchi = 24 orders of branching
  • developing bronchi & lungs grow laterally into the intraembryonic coelom = pleural cavity (houses the lungs)
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7
Q

What are the 4 stages of lung development

A
  • Pseudoglandular stage
  • Canalicular stage
  • Terminal sac stage
  • Alveolar stage
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8
Q

What happens in the pseudoglandular stage

A
  • “The stage p.t. a false gland” (looks like an exocrine gland)
  • This is between weeks 5-17
  • Respiration does not take place (bcos alveoli haven’t been developed)
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9
Q

What happens in the canalicular stage

A
  • This overlaps the pseudoglandular stage (weeks 16-26) bcos its a cranial → caudal development
  • the lumina of the bronchi & bronchioles increase
  • 24 weeks: terminal bronchiolesrespiratory bronchioles, alveolar ducts & terminal sacs
  • lung tissue becomes vascular, respiration may be possible
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10
Q

What happens in the terminal sac stage

A
  • From 26 weeks to birth
  • Terminal sacs develop at the end of the alveolar ducts which capillaries bulging into then = alveoli
    2 types of alveolar cells
  • Type I = squamous shaped
  • Type II produce pulmonary proteins & fats which decrease surface tension (collapsing alveoli)
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11
Q

What happens in the alveolar stage

A
  • from 32 weeks to 8 years
  • Alveocapillary membrane thins bcos capillaries bulge more into the terminal sacs
  • 95% of alveoli form postnatally
  • fetus practices breathing in the uterus
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12
Q

Explain the developent of the diaphragm

A
  • The diaphragm separates the thoracic & abdominal cavities
    develops from 4 sources
  • septum transversum (central tendon of diaphragm)
  • pleuroperitoneal membranes (become a smaller component)
  • dorsal mesentery of the esophagus
  • lateral body walls → peripheral part of the diaphragm
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13
Q

What is congenital diaphragmatic hernia

A
  • It results from failure of the pleuroperitoneal membranes fusing with the other components of the diaphragm (usually on the left)
  • Causes the abdominal organs to enter the thoracic cavity = defective heart & lung development
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14
Q

Explain the development of the larynx

A
  • Larynx develops at the cranial, distal end for the laryngotracheal tube
  • The cartilage of the 4th and 6th pharyngeal arches form the cartilages of the larynx
  • Cranial LT tube mesenchyme → arytenoid swellings that grow towards the tongue → glottis
  • Laryngeal ventricles from epithelial recanalization in week 10
  • Epiglottis formed from hypo pharyngeal eminence
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15
Q

What can cause esophageal atresia

A
  • Defects in the Shh, Wnt, or BMP pathway or mutations of Sox2 or NKX2.1 (dorsoventral patterning)
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