Body Folding & Body Cavities Flashcards
What are the phases of embryonic development?
Growth
Morphogenesis
Differentiation
What causes the pulling and pinching of an embryo into new shapes?
Upregulation and downregulation of cell junctions
What does the growth phase refer to?
Cell division and elaboration of cell products
What does the morphogenesis phase refer to?
Development of shape, size, and other features of a particular organ or part or the whole body
What is morphogenesis controlled by?
Gene expression and regulation in an orderly sequence
What does the differentiation phase refer to?
Cells organized in precise pattern of tissues and organs capable of performing specialized functions
Where does the primordium of the intraembronic coelom first appear?
In the lateral plate mesoderm
What is the lateral plate mesoderm divided into?
Somatic (parietal) layer
Splanchnic (visceral) layer
What is the somatic (parietal) layer of lateral mesoderm continuous with?
Extramembryonic mesoderm covering amnion
What is the splanchnic (visceral) layer of lateral mesoderm continuous with?
Extraembryonic mesoderm covering umbilical vesicle
What is the somatopleure?
Somatic mesoderm and overlying embryonic ectoderm that forms the body wall
What is the splanchnopleure?
Splanchnic mesoderm and underlying embryonic endoderm that forms embryonic gut
When does embryonic head folding begin?
Week 4/day 22
What do the neural folds do during head folding?
Project dorsally and overgrow pharyngeal membrane
What does overgrowth of the neural folds do with regards to other structures?
Moves septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane to ventral surface
During head folding, what happens with the endoderm?
It is incorporated as the foregut
What structures does head folding move into their appropriate locations?
Mouth, heart, and gut tube
What causes folding of the caudal end of the embryo?
Growth of the distal neural tube
After tail folding, the caudal eminence (tail region) projects over what?
The cloacal membrane (future anus)
What germ layer helps form the hindgut and midgut?
Endoderm
Where does the primitive streak lie relative to the cloacal membrane before and after folding?
Before: cranial to cloacal membrane
After: caudal to cloacal membrane
What is the allantois?
Diverticulum of umbilical vesicle
What structures does tail folding reposition?
Hindgut, primitive streak, and cloacal membrane
How do the lateral folds create a cylindrical embryo?
R/L lateral folds extend ventrally toward midline, wrapping around embryo to fuse
What is the omphaloenteric duct?
Connection between umbilical vesicle and midgut
What is gastroschisis?
Protrusion of viscera to the R of the umbilical cord, bowel uncovered and floating in amniotic fluid
Caused by failure of lateral body folds to fuse properly
What is a congenital epigastric hernia?
Midline bulge of abdominal wall between xiphoid process and umbilicus, bowel not exposed
What is the intraembryonic coelom divided into?
Pericardial cavity
Pleural cavities
Peritoneal cavity
What are the pericardial, pleural, and peritoneal cavities lined with?
Mesothelium
What is the location of the pericardial cavity after head folding?
Anterior to foregut and cranial to septum transversum
What does the pericardial cavity open into?
Pericardioperitoneal canals (x2), lateral/dorsal to foregut and dorsal to septum transversum
What is the dorsal mesentery?
Suspends caudal foregut, midgut, and hindgut in the peritoneal cavity
What is the septum transversum?
Primordium of central tendon of diaphragm
What folds grow from the body wall to separate the cavities?
Pleuropericardial folds (cranial) and pleuroperitoneal folds (caudal)
What grows into the pericardioperitoneal canals that cause the cavity to expand?
Bronchial buds
When the bronchial buds grow ventrally, what happens?
They push through the mesenchyme separating it into an outer layer (thoracic wall) and an inner layer (fibrous pericardium)
When do the pleuroperitoneal membranes fuse with the dorsal mesentery of the esophagus and septum transversum?
Week 6
What type of cell migrates into the pleuroperitoneal membrane to complete the closure process?
Myoblasts
Which side of the pleuroperitoneal opening closes first?
R slightly before L
What makes up the diaphragm?
Septum transversum
Pleuroperitoneal membranes
Dorsal mesentery
Myoblasts
How is the phrenic nerve formed?
Myoblasts pull ventral rami (C3-C5) with them and pass through pleuropericardial membranes
What is a congenital diaphragmatic hernia (CDH)?
Viscera bulges into pleural cavity, usually on L side. May involve delayed lung maturation of polyhydramnios, can be corrected at birth
