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58 Cards in this Set

  • Front
  • Back
when is the gut tube formed?
during the third week of gestation
what causes the gut tube to form?
cephalocaudal and lateral folding of the embryo
How many primary bronchi do the left and right lungs have?
-right lung has 3 primary bronchi
-left lung has 2 primary bronchi
the trachea is directly anterior to
the esophagus

-posterior wall of trachea is trachealis muscle and is directly next to esophageal muscle
When does cartilage wrapped around the airway passages end?
right before terminal bronchioles
cephalocaudal folding
-amnion grows faster than yolk sac- posterior end is anchored in chorionic sac
-amnion overgrows front of yolk sac- hinge at prochordal plate which becomes the bucopharyngeal membrane
phayrngeal gut
most superior part of gut- forms nose, nasal passages, pharynx to larynx
foregut derivatives
-esophagus
-tracheobronchial system
-liver
-spleen
-pancreas
lung bud
out-pouching in anterior surface of foregut that quickly divides into bilobar structure (bifurcates)
laryngotracheal groove
slit that is the doorway leading to the out-pouch (lung bud) on ventral side of pharynx
tracheo-esophageal septum
-separates respiratory system (trachea) from the digestive system (esophagus)
-formed by pinching on both sides and then separation- unknown mechanism
-muscular walls on borders of tubes
Failure of proper tracheo-esophageal septum formation results in what two problems
1) esophageal atresia
2) tracheoesophageal fistula

or a combination of the same or both
esophageal atresia
as the two tubes come down the esophagus ends blindly- does not connect with the trachea
tracheoesophageal fistula
-part of esophagus is attached to the trachea forming a fistula
-esophagus communicates with trachea
Branching pattern of ducts controlled primarily by
mesenchyme
Functionality of branched ducts determined by
epithelium
What type of tissue is attenuated/ replaced over the course of lung development?
mesenchyme
FGF-10 is secreted by
mesenchyme
FGF-10
stimulates tip of bud (epithelial cells) to develop/ undergo mitosis
tip epithelium secretes
-BMP-4
-SHH

*only epithelial cells at the tip of the lung bud
SHH and BMP-4
when they reach a critical concentration INHIBIT secretion of FGF-10 locally
When FGF-10 secretion inhibited what occurs?
epithelial mitosis stopped locally- formation of new tips adjacent to distal edges (thus bifurcating)
SHH stimulates mesenchyme to secrete
TGF-beta
TGF-beta
-produced by mesenchyme when stimulated by SHH
-promotes secretion of ECM molecules: fibronectin, collagen I, III, IV
increased connective tissues
make a solid area for the tip to push against and further tell epithelial cells to stop dividing in this area
VEGF release from
mesenchyme under epithelial stimulation
VEGF
invites capillaries to form around it in areas where buds are dividing
How does the epithelium know where the lumen or surface is located in a tube?
-epithelial cells are polarized
-epimorphin released from mesenchyme signals location of basal region
How do epithelial cells know to remain in sheets or tubes?
-tenascin and syndecan produced by the mesenchyme tell the epithelial cells to stay flat and not form layers
order of phases of lung development
1) embryonic period
2) pseudoglandular stage
3) canalicular stage
4) saccular stage
5) alveolar stage
6) maturation
7) growth
What stages occur postnatally in humans?
-alveolar stage
-maturation
-growth
At what stage of lung development is a human born in?
early alveolar stage
How many generations of branching occur before birth?
23

-4 more after birth = 27 total
During what stage of lung development is surfactant first secreted?
-saccular stage
Around what weeks gestation is surfactant first secreted?
week 25-26
What occurs during the embryonic stage?
-lung bud arises from the foregut
-branches 3 times to form primordia of 2 lungs, 5 lobes and the bronchiopulmonary segments
What occurs during pseudoglandular stage?
-respiratory trees branch 14 more times to form the terminal bronchioles
What occurs during the canalicular stage?
-terminal bronchioles divide into 2+ repiratory bronchioles
-respiratory vasculature begins to develop
What occurs during the saccular stage?
-respiratory bronchioles subdivide into terminal sacs that are continuously produced into childhood
-Type I and Type II pneumocytes appear
-surfactant is first secreted
What occurs during the alveolar stage?
-alveoli develop and mature
-great increase in surface area
When does human lung development finish?
around 7-8 years of age
What is lung volume in utero?
about 60% what it will be postnatally
hypoplastic lung
-lungs never develop to saccular stage
diaphragmatic hernia
when diaphragm is not formed properly and there is an absence of pleuroperitoneal membrane on the left side, spleen and intestines move up into the thorax (can cause hypoplastic lung)
what happens if diaphragm not formed properly on the right side
because the liver is there as a boundary nothing can move up into the thorax
postnatal diaphragmatic hernia repair
possible, but lungs may still remain hypoplastic & immature (survival is not certain)
Why are infants so pudgy especially in their bellies?
intestines confined to abdominal region and thus pushing out is the only place they can go
1 cubic mm of lung tissue contains how many alveoli?
170
At what age are most of your alveoli present?
by the end of the second year
When born an infant has how long is the respiratory bronchiole? What does it become when lung development is finished?
0.6 mm at birth becomes 4 mms long when lung development is finished
rat lung development
-alveoli do not appear until post natal day 4
-finished by 3 weeks old
monkey lung development
-have all alveoli at birth
Why is it important to understand lung development in other animals?
-events are the same but timing is different
-must make sure we are looking at effects of drugs on lung development at same lung development stage, etc
What is the critical factor in species selection for models of the human pediatric lung
timing of alveolar development
Where does laryngotracheal groove appear?
on the ventral aspect of the caudal pharynx
respiratory diverticulum (aka lung bud) is composed of
endoderm surrounded by splanchnic mesoderm
How does the respiratory diverticulum become separated from the gut tube?
by being gradually pinched off through the growth of a tracheo-esophageal septum
At birth what fraction of adult alveoli are present?
1/8- 1/6