TBL9 - Body Cavities and Diaphragm Flashcards
What lines the yolk sac in an embryo? What does the lateral plate mesoderm split into? What is the resulting space between the layers called?
1) Endoderm lines the yolk sac
2) The bilateral lateral plate mesoderm splits into parietal and visceral layers (aka parietal mesoderm and visceral mesoderm)
3) The resulting space between the layers creates the embryonic (primitive) body cavity
How is the anterolateral body wall closed in an embryo? What is the fate of the yolk sac? How is the gut tube formed?
1) The surface ectoderm and parietal mesoderm form bilateral body wall folds that fuse in the midline to close the anterolateral body wall
2) The yolk sac is obliterated
3) The endoderm and visceral mesoderm fuse in the midline to close the gut tube, which is surrounded by the parietal mesoderm-lined body cavity
What do the two layers (parietal & visceral) of mesoderm differentiate into?
Mesenchymal cell differentiation transforms both layers of mesoderm into thin, underlying layers of loose connective tissue covered by simple squamous epithelia designated mesothelium
What suspends the gut tube from the posterior body wall into the body cavity in an embryo?
Continuity of the parietal mesoderm with the visceral mesoderm forms the dorsal mesentery that suspends the gut tube from the posterior body wall into the body cavity
What are the three parts of the gut tube? What forms adjacent to the foregut?
1) The endoderm-lined gut tube includes the foregut, hindgut, and interconnecting midgut
2) Adjacent to the foregut, the primitive heart tube forms in the pericardial cavity
What separates the pericardial cavity from the distal foregut, midgut, and hindgut? How do the lung bud and liver bud arise?
1) The pericardial cavity is separated from the distal foregut, midgut and hindgut by the septum transversum, a wedge of visceral mesoderm
2) The lung bud and liver bud arise by invaginations of the distal foregut endoderm into the pericardial cavity and septum transversum, respectively
What happens as closure of the gut tube and anterior body wall is completed?
1) Closure of the gut tube is initially incomplete where the vitelline duct connects the midgut to the yolk sac
2) As closure of the gut tube and anterior body wall is completed, the vitelline duct and obliterated yolk sac become incorporated into the connecting stalk and undergo degeneration
What does the septum transversum horizontally separate? What maintains continuity between the pericardial and peritoneal cavities as growth of the liver progresses into the septum transversum?
1) The septum transversum horizontally separates the pericardial cavity from the primitive abdominal (aka peritoneal) cavity
2) Pericardioperitoneal canals on each side of the foregut maintain continuity between the pericardial and peritoneal cavities as growth of the liver progresses into the septum transversum
What do the pleuropericardial folds project as during growth of the lung buds? What does thinning of these folds result in? What separates the central pericardial cavity from the bilateral pleural cavities?
1) Pleuropericardial folds project as small ridges into the pericardial cavity during growth of the lung buds
2) Thinning of the projecting folds transforms them into pleuropericardial membranes
3) Fusion of the membranes vertically separates the central pericardial cavity from the bilateral pleural cavities
What is the parietal pleura and visceral pleura formed from?
Parietal pleura that lines the pleural cavities and visceral pleura that covers the lungs are formed by the parietal mesoderm and visceral mesoderm, respectively
What creates the pleuroperitoneal membranes?
Pleuroperitoneal folds project into the caudal ends of the bilateral pericardioperitoneal canals and subsequent thinning of the folds creates the pleuroperitoneal membranes
What horizontally separates the pericardial cavity and bilateral pleural cavities from the peritoneal cavity?
1) Fusion of the pleuroperitoneal membranes with the septum transversum horizontally separates the pericardial cavity and bilateral pleural cavities from the peritoneal cavity
2) The pleuropericardial folds and septum transversum form in the cervical region
What becomes the central tendon of the diaphragm? What initiates muscular ingrowth into the pleuroperitoneal membranes? What forms the muscular portion of the diaphragm?
1) The septum transversum becomes the central tendon of the diaphragm
2) Muscular ingrowth into the pleuroperitoneal membranes is initiated by myoblasts from somites C3-C5
3) Continued ingrowth and the differentiation of skeletal muscle fibers forms the muscular portion of the diaphragm, which surrounds the central tendon
From the spinal cord, what grows into the pleuropericardial folds and septum transversum during formation of the diaphragm? What repositions the diaphragm and phrenic nerves to the lower thoracic region?
1) After arising from spinal cord segments C3-C5, the phrenic nerves grow into the pleuropericardial folds and septum transversum during formation of the diaphragm
2) Rapid growth of the vertebral column relative to the anterior portion of the embryo repositions the diaphragm and phrenic nerves to the lower thoracic region
What do phrenic nerves provide to the diaphragm? What is the most peripheral part of the muscular diaphragm formed by? What is therefore the resulting innervation of this part?
1) Phrenic nerves provide somatic sensory and motor innervation to most of the diaphragm
2) The most peripheral part of the muscular diaphragm is formed by myoblasts from the parietal mesoderm of the thoracic wall; thus, the peripheral diaphragm is innervated by the lower thoracic spinal nerves
