Body Cavity Development Flashcards
Deuterostomes?
- second mouth
- we from a tube with ectoderm on outside
- endoderm inside
- mesoderm in between
Coelom? what forms it?
- body cavity
- forms within mesoderm
What layer controls what we bring in?
Endoderm
-nutrients, air
Oropharyngeal membrane?
- cranial end where ectoderm and endoderm come in contact
- will become mouth
Cloacal membrane?
- caudal end where ectoderm and endoderm come in contact
- will become anus
What axes do the three layers fold in?
- lateral
- cranial-caudal
Lateral folding starts when?
3rd week
Early formation of Coelom (day 19)?
-lateral plate mesoderm forms small openings called intercellular clefts
Splitting of lateral plate mesoderm (day 20)?
- intercellular clefts separate the somatic (parietal) mesoderm from splanchnic (visceral) mesoderm
- this space is called intraembryonic coelom or embryonic body cavity
Mushroom stage (day 21)?
- amniotic sac begins to surround embryo
- yolk sac begins to narrow
- intraembryonic and extra embryonic coeloms still connected
Isolation of embryonic coelom (day 24)?
- somatic mesoderm encompasses intraembryonic coelom
- splanchnic mesoderm surrounds nascent gut tube to form dorsal and ventral mesenteries
- gut tube still connected to yolk sac
Body cavity closure (end of 4th week)?
- fusion of somatic (parietal) mesoderm to form ventral body wall
- splanchnic (visceral) mesoderm of ventral mesentery breaks down to form continuous left and right intraembryonic coelom
- gut contained within splanchnic mesoderm and is connected to dorsal body wall by dorsal mesentery
Allantois?
- forms part of urogenital system
- hindgut
Angiogenic cell cluster?
- future heart
- more cranial and distal to oropharyngeal membrane
Cranial caudal folding (day 22)?
- folding of endoderm at cranial and caudal ends
- foregut
- hindgut forms
- pericardial cavity forms under cranial portion
- septum transversum adjacent to heart and gut tube
Site of lung bud formation?
foregut
Liver bud forms where?
- midgut
- forms in the septum transversum (expands toward foregut)
Pleuropericardial folds (5th week)?
- expands dorsomedially to separate pleural and pericardial cavities
- each contain phrenic nerve
- forms fibrous pericardium
Pleuroperitoneal folds?
- expands ventrally to fuse with septum transversum and foregut mesentery
- separates pleural and peritoneal cavities
Formation of diaphragm (7th week)?
- combination of septum transversum (central tendon), pleuroperitoneal membranes, mesoderm from body wall and esophageal mesenchyme (crura)
- muscle migrates from cervical myotomes with phrenic nerve (C3, 4, 5) and neighboring body wall
Congenital Diaphragmatic Hernia (foramen of Bochdalek)?
- insufficient growth of pleuroperitoneal folds or failure of folds to fuse with septum transversum and/or esophageal mesentery
- happens more on left side
- surgical repair at birth or prenatally as long as not severe pulmonary insufficiency (lungs not forming)
Congenital Esophageal Hernia?
- delay in descent of stomach so that diaphragm forms around it leaving an expanded esophageal hiatus
- common, symptomatic in middle age
- congenital shortness of esophagus leaving stomach permanently trapped and potentially constricted by diaphragm
- uncommon, symptomatic in childhood
Congenital Eventration of Diaphragm?
- failure of muscle to migrate from body wall to diaphragm (10th week)
- weak diaphragm can balloon into thoracic cavity leading to potential hypo plastic lungs
- rare, symptomatic any age
Sternal cleft?
- failure of left and right somatic mesoderm to fuse
- commonly asymptomatic
- surgical repair at birth
Ectopia Cordis?
-failure of lateral wall closure results in heart lying outside body cavity
Cantrell Pentalogy?
spectrum that includes ectopia cordis, anterior diaphragm defects, absence of pericardium, sternal cleft, abdominal wall defects (omphaloceles and gastroschisis)
What forms the lung buds?
respiratory diverticulum from ventral wall of foregut
What genes are expressed in the formation of lung buds?
- Nkx2.1 expression in ventral endoderm of foregut tube
- induced by mesodermal expression of Fgf10 and Wnt2/2b
What separates the trachea from the esophagus?
-mesodermal ridges expand under influence of Wnt signaling to separate them
What gives rise to the lobes of the lung?
- secondary bronchial buds give rise to each lobe of lung
- 3 buds in right lung and 2 buds in left lung
- in 6th week tertiary buds form the bronchopulmonary segments of mature lung
What separates pleural and pericardial cavities?
pleuroperitoneal folds
What becomes visceral pleura?
- splanchnic mesoderm
- highly vascularized
What becomes parietal pleura?
-somatic mesoderm
16th week of lung development?
14 rounds of branching occurs to produce terminal bronchioles
16-28 weeks of lung development?
further division into respiratory bronchioles
36th week of lung development?
- formation of mature alveoli
- continues into childhood
Molecular control of bronchial branching?
- mesodermal expression of Fgf10 induces mitosis and outgrowth of respiratory duct
- BMP4 in apical epithelial cells inhibits mitosis
- Tgfb1 inhibits Fgf10 and promotes matrix synthesis and maturation
- Fgf10 expression lateral to tip induces new outgrowth in either direction
Stages of Lung development?
- Embryonic (weeks 4-7)
- respiratory diverticulum
- initial branching - Pseudoglandular (weeks 8-16)
- 14 generations of branching, terminal bronchioles - Canalicular (weeks 17-26)
- respiratory bronchioles - Terminal sac (weeks 26-36)
- specialized cells, surfactant - Alveolar (weeks 36 to birth)
- maturation of alveoli - Postnatal
- growth of existing alveolar sacs
Tracheoesophageal Fistulas?
- abnormal separation of tracheal bud from esophagus
- allow milk and stomach fluids to be aspirated into lungs
- build up of amniotic fluid as it cannot be swallowed and returned to mother via fetal circulation
- surgically repair
Tracheal or pulmonary genesis?
- abnormal formation of lung buds or early branching
- bilateral or unilateral
- incompatible with life
Gross malformation of lungs?
- irregular branching leading to abnormal lobation
- asymptomatic
Respiratory distress syndrome?
- birth after 26 weeks (terminal sac stage) infant has good change at survival
- lungs rapidly maturing and thinning alveolar walls dependent on proper production of pulmonary surfactant by type 2 alveolar cells
- labored breathing and poor oxygenation
- can lead to bronchopulmonary dysplasia
