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Respiratory System
- Endoderm
- Primitive pharynx-6th arch
- Laryngotracheal groove-transcient and invaginates to form the laryngotracheal diverticulum-forms the respiratory bud
- Tracheoesophageal folds-migrate towards midline to form tracheoesophageal septum (trachea and esophagus as own tube now)
- Larngotracheal tube
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Trachea
- Endoderm
- -epithelium (lining of trachea) and glands
- -lungs
- Spanchnic mesenchyme
- -cartilage
- -connective tissue-B.V. and lymph
- -muscles (smooth)
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Abnormalities in foregut
- esophageal atresia-tracheoesophageal folds migrating towards midline and something goes wrong
- liquid/food into lungs-connection of esophageus into trachea
- can be seen on ultrasound and corrected with surgery
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Bronchi and Lungs
- Endoderm
- Lung bud
- Bronchial buds
- -Primary bronchus-left and right lung
- -secondary bronchi-lobar-three on right (superior, middle, inferior); two on left: superior, inferior
- -segmental bronchi-ten right, nine left
- bronchialpulmonary segment-24 weeks, 17 orders of branches, terminal bronchioles
- *Conduction system intact-way to get air into lungs
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Pseudoglandular (5-17 weeks) Lung Development
- Connective tissue-mesoderm
- -not close enough to sacs to have gas exchange
- -can't survive
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Canalicular (16-24 weeks) Lung Development
- Vascularization-mesoderm
- respiratory bronchioles and terminal sacs (primitive alveoli)
- +/- survival-depends: closer to 24 50% chance
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Terminal sac (24 weeks-birth) Lung Development
- Differentiation of cells
- gas exchange
- squamous epithelium=type I pneumocytes-gas exchange flat-endoderm
- lymphatic capillaries-mesoderm
- secretory epithelial cells=type II pneumocytes-surfactant-protein that reduces surface tension and keep alveoli open so don't collapse down-endoderm
- -will survive
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Alveolar (+8 years)
- Alveolocapillary membrane-mesoderm (gas exhange and vascular capillaries touching) and endoderm (squamous epithelium
- Primitive alveoli-form more primitive alveoli-endoderm-up to 3 years-some up to 8 years
- -mature alveoli
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Formation of the Body Cavities: Coelom and Mesenteries
- Pericardial cavity: heart
- Pericardioperiotoneal canals: partitions form in each canal (lungs develop here)
- -seperates pericardial cavity from the pleural cavities
- -seperate pleural cavities from the peritoneal cavity (abdomine)
- Pleural cavities: lung
- Peritoneal cavity: abdomen
- *pictures*
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Pericardial Cavity
- 4th week
- lateral folds
- -endocardial primordia (heart inner lining start with 2 heart tubes)-mesoderm
- -pericardial coelom-lateral to heart tubes
- -somatic vs. splanchinic layers-mesentaries suspend heart and GI tract from wall-double layers of spanchnic mesoderm
- Head folds
- -heart-most cephalic (mesoderm)
- -septum transversum-above heart-moves below after folding (mesoderm)
- septum transversum
- -become diaphragm
- pericardioperitoneal canals-surround space for lungs/surround heart and septum transversum
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Pericardioperitoneal Canals
- Two
- Lies lateral to the proximal part of the foregut (esophagus) and dorsal to the septum transversum
- one continuous tube
- arbitrarily divide it into 3 regions
- -region 1 and 3 become pleural cavities
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Pleuropericardial Folds
- Due to growth of the bronchial buds into the pericardioperiotoneal canals (mesoderm)
- Enlarge and form partitions that separate the pericardial cavity from the pleurla cavities
- Formation of: pleural cavity, pericardial cavity(heart), primitive mediastimun (between lungs)
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