Respiratory Slide Show

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Nostrils Nasal Cavity   Nasopharynx   Larynx
  Trachea   Bronchi   Bronchioles Alveolii
Path of Air into Lungs
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• Thyroid cartilage
• Arytenoid cartilage
• Cricoid cartilage
• Interarytenoid muscle

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• Vestibule
• False vocal cord
• True vocal cord
• Trachea

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Recanalization of Larynx
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Gut Mesenchyme
Thoracic Mesenchyme
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Pseudoglandular phase (5-17 weeks) Further
branching of the duct system (up to 21 further
orders) generates the presumptive conducting
portion of the respiratory system up to the
level of the terminal bronchioles. At this time
the future airways are narrow with little lumens
and a pseudostratified squamous epithelium. They
are embedded within a rapidly proliferating
mesenchyme. The structure has a glandular
appearance.   Canalicular phase (15-25
weeks) The onset of this phase is marked by
extensive angiogenisis within the mesenchyme that
surrounds the more distal reaches of the
embryonic respiratory system to form a dense
capillary network. The diameter of the airways
increases with a consequent decrease in
epithelial thickness to a more cuboidal
structure. The terminal bronchioles branch to
form several orders of respiratory bronchioles.
Differentiation of the mesenchyme progresses
down the developing respiratory tree, giving rise
to chondrocytes, fibroblasts and myoblasts.  
Terminal sac phase (24-40weeks) Branching
and growth of the terminal sacs or primitive
alveolar ducts. Continued thinning of the stroma
brings the capillaries into apposition with the
prospective alveoli. Functional type-II
pneumonocytes differentiate via several
intermediate stages from pluripotent epithelial
cells in the prospective alveoli. Type I
pneumonocytes differentiate from cells with a
type-II like phenotype. These cells then flatten,
increasing the epithelial surface area by
dilation of the saccules, giving rise to immature
alveoli. By 26 weeks, a rudimentary though
functional blood/gas barrier has formed.
Maturation of the alveoli continues by further
enlargement of the terminal sacs, deposition of
elastin foci and development of vascularised
septae around these foci. The stroma continues to
thin until the capillaries protrude into the
alveolar spaces.   Alveolar phase (36 weeks
- term/adult) Maturation of the lung
indicated by the appearance of fully mature
alveoli begins at 36 weeks, though new alveoli
will continue to form for approximately three
years. A decrease in the relative proportion of
parenchyma to total lung volume still
contributes significantly to growth for 1 to 2
years after birth, thereafter all components
grow proportionately until adulthood.
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