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2017 ; 367
(3
): 427-444
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Development of the lung
#MMPMID28144783
Schittny JC
Cell Tissue Res
2017[Mar]; 367
(3
): 427-444
PMID28144783
show ga
To fulfill the task of gas exchange, the lung possesses a huge inner surface and
a tree-like system of conducting airways ventilating the gas exchange area.
During lung development, the conducting airways are formed first, followed by the
formation and enlargement of the gas exchange area. The latter (alveolarization)
continues until young adulthood. During organogenesis, the left and right lungs
have their own anlage, an outpouching of the foregut. Each lung bud starts a
repetitive process of outgrowth and branching (branching morphogenesis) that
forms all of the future airways mainly during the pseudoglandular stage. During
the canalicular stage, the differentiation of the epithelia becomes visible and
the bronchioalveolar duct junction is formed. The location of this junction stays
constant throughout life. Towards the end of the canalicular stage, the first gas
exchange may take place and survival of prematurely born babies becomes possible.
Ninety percent of the gas exchange surface area will be formed by
alveolarization, a process where existing airspaces are subdivided by the
formation of new walls (septa). This process requires a double-layered capillary
network at the basis of the newly forming septum. However, in parallel to
alveolarization, the double-layered capillary network of the immature septa fuses
to a single-layered network resulting in an optimized setup for gas exchange.
Alveolarization still continues, because, at sites where new septa are lifting
off preexisting mature septa, the required second capillary layer will be formed
instantly by angiogenesis. The latter confirms a lifelong ability of
alveolarization, which is important for any kind of lung regeneration.