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58 Cards in this Set
- Front
- Back
when is the gut tube formed?
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during the third week of gestation
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what causes the gut tube to form?
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cephalocaudal and lateral folding of the embryo
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How many primary bronchi do the left and right lungs have?
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-right lung has 3 primary bronchi
-left lung has 2 primary bronchi |
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the trachea is directly anterior to
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the esophagus
-posterior wall of trachea is trachealis muscle and is directly next to esophageal muscle |
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When does cartilage wrapped around the airway passages end?
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right before terminal bronchioles
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cephalocaudal folding
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-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 |
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phayrngeal gut
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most superior part of gut- forms nose, nasal passages, pharynx to larynx
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foregut derivatives
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-esophagus
-tracheobronchial system -liver -spleen -pancreas |
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lung bud
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out-pouching in anterior surface of foregut that quickly divides into bilobar structure (bifurcates)
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laryngotracheal groove
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slit that is the doorway leading to the out-pouch (lung bud) on ventral side of pharynx
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tracheo-esophageal septum
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-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 |
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Failure of proper tracheo-esophageal septum formation results in what two problems
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1) esophageal atresia
2) tracheoesophageal fistula or a combination of the same or both |
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esophageal atresia
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as the two tubes come down the esophagus ends blindly- does not connect with the trachea
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tracheoesophageal fistula
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-part of esophagus is attached to the trachea forming a fistula
-esophagus communicates with trachea |
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Branching pattern of ducts controlled primarily by
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mesenchyme
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Functionality of branched ducts determined by
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epithelium
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What type of tissue is attenuated/ replaced over the course of lung development?
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mesenchyme
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FGF-10 is secreted by
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mesenchyme
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FGF-10
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stimulates tip of bud (epithelial cells) to develop/ undergo mitosis
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tip epithelium secretes
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-BMP-4
-SHH *only epithelial cells at the tip of the lung bud |
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SHH and BMP-4
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when they reach a critical concentration INHIBIT secretion of FGF-10 locally
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When FGF-10 secretion inhibited what occurs?
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epithelial mitosis stopped locally- formation of new tips adjacent to distal edges (thus bifurcating)
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SHH stimulates mesenchyme to secrete
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TGF-beta
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TGF-beta
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-produced by mesenchyme when stimulated by SHH
-promotes secretion of ECM molecules: fibronectin, collagen I, III, IV |
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increased connective tissues
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make a solid area for the tip to push against and further tell epithelial cells to stop dividing in this area
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VEGF release from
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mesenchyme under epithelial stimulation
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VEGF
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invites capillaries to form around it in areas where buds are dividing
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How does the epithelium know where the lumen or surface is located in a tube?
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-epithelial cells are polarized
-epimorphin released from mesenchyme signals location of basal region |
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How do epithelial cells know to remain in sheets or tubes?
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-tenascin and syndecan produced by the mesenchyme tell the epithelial cells to stay flat and not form layers
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order of phases of lung development
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1) embryonic period
2) pseudoglandular stage 3) canalicular stage 4) saccular stage 5) alveolar stage 6) maturation 7) growth |
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What stages occur postnatally in humans?
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-alveolar stage
-maturation -growth |
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At what stage of lung development is a human born in?
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early alveolar stage
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How many generations of branching occur before birth?
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23
-4 more after birth = 27 total |
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During what stage of lung development is surfactant first secreted?
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-saccular stage
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Around what weeks gestation is surfactant first secreted?
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week 25-26
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What occurs during the embryonic stage?
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-lung bud arises from the foregut
-branches 3 times to form primordia of 2 lungs, 5 lobes and the bronchiopulmonary segments |
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What occurs during pseudoglandular stage?
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-respiratory trees branch 14 more times to form the terminal bronchioles
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What occurs during the canalicular stage?
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-terminal bronchioles divide into 2+ repiratory bronchioles
-respiratory vasculature begins to develop |
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What occurs during the saccular stage?
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-respiratory bronchioles subdivide into terminal sacs that are continuously produced into childhood
-Type I and Type II pneumocytes appear -surfactant is first secreted |
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What occurs during the alveolar stage?
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-alveoli develop and mature
-great increase in surface area |
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When does human lung development finish?
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around 7-8 years of age
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What is lung volume in utero?
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about 60% what it will be postnatally
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hypoplastic lung
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-lungs never develop to saccular stage
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diaphragmatic hernia
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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)
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what happens if diaphragm not formed properly on the right side
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because the liver is there as a boundary nothing can move up into the thorax
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postnatal diaphragmatic hernia repair
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possible, but lungs may still remain hypoplastic & immature (survival is not certain)
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Why are infants so pudgy especially in their bellies?
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intestines confined to abdominal region and thus pushing out is the only place they can go
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1 cubic mm of lung tissue contains how many alveoli?
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170
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At what age are most of your alveoli present?
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by the end of the second year
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When born an infant has how long is the respiratory bronchiole? What does it become when lung development is finished?
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0.6 mm at birth becomes 4 mms long when lung development is finished
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rat lung development
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-alveoli do not appear until post natal day 4
-finished by 3 weeks old |
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monkey lung development
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-have all alveoli at birth
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Why is it important to understand lung development in other animals?
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-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 |
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What is the critical factor in species selection for models of the human pediatric lung
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timing of alveolar development
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Where does laryngotracheal groove appear?
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on the ventral aspect of the caudal pharynx
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respiratory diverticulum (aka lung bud) is composed of
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endoderm surrounded by splanchnic mesoderm
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How does the respiratory diverticulum become separated from the gut tube?
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by being gradually pinched off through the growth of a tracheo-esophageal septum
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At birth what fraction of adult alveoli are present?
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1/8- 1/6
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