Lungs and thorax Flashcards
What is the name of the primitive body cavity that is incorporated by embryo?
Intra embryonic coelom
What drives rostral and caudal folding?
Neural tube expansion
What causes lateral folding?
As amnion surrounds embryo brings sides closer together
What does rostral folding do to positioning of rostral structures?
Moves them ventrally (to front)
What structures move ventrally/inferiorly in folding?
Septum transversum (diaphragm)
Buccopharyngeal membrane (mouth)
Cardiogenic region (heart)
Primitive pericardial cavity
What causes heart to lie caudally of brain?
Rostral folding
What drives caudal folding?
Growth of developing spinal cord
Describe the composition of the buccopharnygeal and cloacal membranes?
Just endoderm and ectoderm due to apoptosis of mesoderm
What does caudal folding do?
Cloacal membrane and allantois (forms bladder) moves ventrally
Leads to formation of hindgut tube
Displaces connecting stalk so it merges with neck of yolk sac and both form umbilical cord
What forms umbilical cord?
Caudal folding and expansion of amniotic cavity displaces connecting stalk so it merges with neck of yolk sac
What does lateral folding do to germ layers?
Fusion of 3 germ layers at ventral midline
What does lateral folding do?
Ventral movement of lateral plate mesoderm (parietal and visceral) these fuse forming lining and encloses intraembryonic coelom/cavity (body cavity)
What does somatic mesoderm do?
Coat inside of body wall
What does splanchnic/visceral mesoderm do?
Coats endodermal gut tube and associated structures
Describe what happens to amnion in embryonic folding?
Collapses around embryo and encloses it due to lateral folding (ends of amnion meet)
How does vitelline duct form?
As gut tube forms, neck of yolk sac narrows forming vitelline duct
What does gut tube become suspended in as it attaches dorsal wall?
Coelomic cavity
What is coelomic cavity surrounded by?
Splanchnic mesoderm
What forms ventral body wall?
2 sides of amnion meet in midline through lateral folding and fuse
What eventually forms the diaphragm?
Septum transversum (from mesoderm)
What is the septum transversum derived from?
Mesoderm
What is intraembryonic coelom partially divided into and what by?
Thoracic (pericardial) and abdominal (peritoneal) portions by septum transversum
What seals of pericardial peritoneal canals?
Pleuroperitoneal membranes (develop from pleuroperitoneal folds)
How does the pericardium divide?
Pleuropericardial folds originate along lateral body wall and fuse medially
Divide primitive pericardial cavity into definitive pericardial cavity and 2 pleural cavities
What 4 elements make up the diaphragm, what do they give rise to in the adult diaphragm?
Septum transversum - central tendon
Pleuroperitoneal membrane - posterior diaphragm
Paraxial mesoderm of body wall - muscular rim
Dorsal oesophogeal mesentry (L1-L3) gives rise to diaphragmatic cruca
What part of the diaphragm does the septum transversum give rise to?
Central tendon
What part of the diaphragm does the pleuroperitoneal membrane give rise to?
Posterior diaphragm
When does septum transversum arise?
Day 22
Where does septum transversum originally lie then what happens to it?
Lies rostral to cardiogenic region
Then carried ventrally by rostral folding so wedges between cardiogenic region and neck of yolk sac
What does septum transversum attach to?
Anterior body wall (T7), lateral body wall, oesophogeal mesentry (T12)
What layer are epithelium of alveoli, bronchi and trachea and larynx from?
Endoderm
How and when does respiratory system first develop?
Buds off ventral wall of foregut in week 4
What layer (and type) gives rise to muscles, cartilage and connective tissue of the respiratory system?
Splachnic mesoderm
What happens as respiratory bud elongates?
Forms trachea and lung bud appears at caudal end.
When does lung bud split into left and right bronchi?
Day 28
How does entire bronchial tree form?
Lung endoderm develops by branching morphogenesis and budding forms entire bronchial tree
What coats the lung endoderm, what does it give rise to?
Mesenchymal tissue from splanchnic mesoderm - diff into cartilaginous rings around trachea etc
What does lung endoderm differentiate to?
Respiratory epithelium
At what point can gaseous exchange between blood and air occur?
7th month
Does the septum transversum initially fully divide the thorax and abdomen?
No leaves huge canals called the pericardioperitoneal canals.
What canals does the septum transversum leave?
Pericardioperitoneal canals
Where do the lung buds grow into (canals)?
Pericardioperitoneal canals.
Is the central tendon of the diaphragm muscular?
No
What closes the pericardioperitoneal canals?
Pleuroperitioneal membranes
