DEVELOPMMENT

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DEVELOPMMENT OF RESPIRATORY SYSTEM
Dr. Ahmed Fathalla Ibrahim
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LOWER RESPIRATORY ORGANS

• LARYNX
• TRACHEA
• BRONCHI
• LUNGS

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PHARYNGEAL ARCHES
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RESPIRATORY PRIMORDIUM
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RESPIRATORY PRIMORDIUM
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RESPIRATORY PRIMORDIUM
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RESPIRATORY PRIMORDIUM

• Begins to form in the middle of 4th week
• Laryngotracheal groove a median outgrowth from
  the caudal end of the floor (ventral wall) of
  primordial pharynx, caudal to 4th pharyngeal
  pouch
• Respiratory diverticulum produced by deepening
  (evagination) of the groove, located ventral to
  caudal part of foregut

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RESPIRATORY PRIMORDIUM

• Tracheal bud it is the enlarged distal end of
  diverticulum
• Longitudinal tracheoesophageal folds develop in
  diverticulum, approach each other fuse to form
  tracheoesophageal septum dividing cranial part of
  foregut into
• Ventral part laryngotracheal tube primordium of
  larynx, trachea, bronchi lungs
• Dorsal part pharynx, esophagus
• Both parts maintain communication through
  primordial laryngeal inlet

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EMBRYOLOGICAL ORIGIN

• Endoderm lining laryngotracheal tube epithelium
  glands of all respiratory organs
• Fourth sixth pharyngeal arch cartilages all
  laryngeal cartilages EXCEPT epiglottis
• Sixth pharyngeal arch muscles intrinsic muscles
  of larynx
• Mesenchyme of hypopharyngeal eminence epiglottis
• Splanchnic mesoderm surrounding foregut
  connective tissue, cartilage, smooth muscles,
  blood lymphatic vessels of trachea, bronchi
  lungs

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DEVELOPMENT OF BRONCHI LUNGS
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DEVELOPMENT OF BRONCHI LUNGS

• During 5th week, tracheal bud divides into 2
  primary bronchial buds
• Main bronchus formed by primary bronchial bud
  together with its surrounding splanchnic
  mesoderm, divided into secondary (lobar),
  tertiary (segmental) intrasegmental branches
• By 24 weeks, 17 orders of branches have formed
  respiratory bronchioles have developed
• After birth, 24 orders of branches are present

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DEVELOPMENT OF BRONCHI LUNGS

• As the lungs expand
• They invaginate pleura acquire a visceral layer
  of pleura (derived from splanchnic mesoderm)
• They grow caudally into body wall lie close to
  heart. The thoracic body wall becomes lined by a
  parietal layer of pleura (derived from somatic
  mesoderm)

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MATURATION OF LUNGS

1. Pseudoglandular period
2. Canalicular period
3. Terminal saccular period
4. Alveolar period

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MATURATION OF LUNGS
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PSEUDOGLANDULAR PERIOD (6-12 WEEKS)

• Lung resembles an exocrine gland
• Only bronchial primordial terminal bronchioles
  are formed
• Respiration is not possible

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CANALICULAR PERIOD (16-26 WEEKS)

• Lumina of bronchi terminal bronchioles enlarge
• Respiratory bronchioles alveolar ducts develop
• Lung tissue becomes highly vascular
• Respiration is possible
• Fetus born at this period often dies because of
  immaturity of systems

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TERMINAL SACCULAR PERIOD (26 BIRTH)

• Alveolar ducts give rise to terminal saccules
  (primordial alveoli)
• Terminal saccules cuboidal epithelium begins to
  change into squamous
• Capillaries begin to bulge into alveoli to
  establish blood-air barrier that permits adequate
  gas exchange
• Terminal saccules are lined with
• Type I pneumocytes (across which gas exchange
  occurs) main type of cells
• Type II pneumocytes (secrete surfactant)

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TERMINAL SACCULAR PERIOD (26 BIRTH)

• Surfactant
• Role counteracts surface tension forces
  facilitates expansion of alveoli
• Production begins by 20 weeks increases during
  last 2 weeks of pregnancy
• By 26-28 weeks surfactant is produced in
  sufficient amount for survival of prematurely
  born fetus

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ALVEOLAR PERIOD (32 WEEKS 8 YEARS)

• Number of respiratory bronchioles and terminal
  saccules (primordial alveoli) increases
• Type I pneumocytes of terminal saccules becomes
  extremely thin squamous so that adjacent
  capillaries bulge into it
• Alveolocapillary membrane is sufficiently thin to
  allow gas exchange

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ALVEOLAR PERIOD (32 WEEKS 8 YEARS)

• Lungs begin to work after birth
• Transition from dependence on placenta for gas
  exchange to lungs requires
• Production of sufficient amount of surfactant
• Development of alveolocapillary membrane that is
  sufficiently thin

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ALVEOLAR PERIOD (32 WEEKS 8 YEARS)

• Maturation of alveoli (about 95) occurs after
  birth
• From birth to third year Increase in size of
  lungs is mostly due to increase in number of
  respiratory bronchioles primordial alveoli
• Immature alveoli have the potential for forming
  additional primordial alveoli
• Immature alveoli increases in size become mature

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TRACHEOESOPHAGEAL FISTULA
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TRACHEOESOPHAGEAL FISTULA

• Most common anomaly
• Associated with esophageal atresia in more than
  85 of cases
• Often associated with polyhydramnios
• Cause incomplete fusion of treacheoesophageal
  folds resulting in a defective tracheoesophageal
  septum faulty partitioning of foregut into
  trachea esophagus

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TRACHEOESOPHAGEAL FISTULA

• Clinical manifesttaions
• Infants cough choke when swallowing (due to
  accumulation of saliva in upper respiratory
  tract)
• Infants regurgitate when swallowing milk (milk
  fills esophageal pouch is regurgitated)
• Pneumonitis

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RESPIRATORY DISTRESS SYNDROME

• Also known as hyaline membrane disease
• Affects about 2 of newborn (especially premature
  newborn)
• Cause deficiency of surfactant
• Manifestation lungs are underinflated, alveoli
  contain a fluid with a high protein content that
  resembles a hyaline membrane

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RESPIRATORY DISTRESS SYNDROME

• Predisposing factors
• Prolonged intrauterine asphyxia
• Deficiency of thyroxine
• Treatment glucocorticoid

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OTHER ANOMALIES

• Stenosis (narrowing) or atresia (obstruction) of
  trachea due to unequal partitioning of foregut
  into esophagus trachea
• Congenital lung cysts disturbance in bronchial
  development leads to dilation of terminal bronchi
  formation of cysts filled with fluid or air
• Agenesis of lung due to failure of bronchial bud
  to develop