Lecture 2: Body Folding and Body Cavities Flashcards
What causes body folding?
Up/downregulation of cell junctions and growth of cells allow embryo to fold a certain way
What happens in these phases of embryo development?
Growth
Morphogenesis
Differentiation
- cell division and elaboration of cell products
- develops features of organs/part of body
- cells form patterns of tissues that have specialized functions
What is the intraembryonic coelom?
Empty U-shaped cavity that develops from spaces forming in the lateral plate and cardiogenic mesoderm
The spaces in the lateral plate mesoderm forms what layers and what parts of the lateral mesoderm? What is each part continuous with?
Somatic (parietal) - amnion mesoderm
Splanchnic (visceral) = umbilical vesicle mesoderm
What is the somatopleure and sphlanchopleure?
Somatic mesoderm + covering ectoderm
Splanchnic mesoderm + covering ectoderm
Describe the nature of embryo folding in different planes (Cranial, caudal, lateral)
Embryo transforms from flat to cylindrical. All parts fold simultaneously, but cranial folding is fast and lateral sides lag behind.
Describe the steps to cranial folding:
- Elongation on both ends (4th week, Day 22)
- Neural fold travels downward and backward and covers the oropharyngeal membrane
- Neural fold growth causes movement of the septum transversum, intraembryonic coelom, primordial heart to correct positions
- Foregut endoderm is incorporated
After cranial folding, what happens to the intraembryonic coelom?
Pericardial cavity
Pericardioperitoneal canals
Forms the pericardial cavity (Ventral to foregut) which opens to 2 pericardioperitoneal canals (dorsal) on either side of the foregut
Describe the process of caudal folding:
- Caudal eminence grows over the cloacal membrane (future anus)
- Part of the endoderm forms the hindgut and then end dilates to form the cloaca (rudiment of bladder/rectum)
What happens after caudal folding?
1) Primitive Streak now caudal to cloacal membrane
2) Moves cloacal membrane (future anus) to correct position
3) Endoderm is incorporated into hindgut
Describe how the lateral fold happens
Lateral edges wrap around the embryo and fuse
Umbilical vesicle is compressed and pinches off
Endoderm gut tube is now enclosed
Gastroschisis
Protruding uncovered bowel, exposed to salty amniotic fluid. Usually located right of midline
Congenital epigastric hernia
Herniation but bowel not exposed to amniotic fluid. Usually located on the midline.
What cavities are formed from the division of the intraembryonic coelom?
Pericardial, pleural and peritoneal cavity
What lines the cavities? What are the walls derived from? What layer of the peritoneum do these walls form?
Mesothelium
Parietal wall - somatic mesoderm, parietal layer
Visceral wall - splanchnic mesoderm, visceral layer
What is the dorsal mesentery?
Suspends the caudal foregut, midgut and hindgut in the peritoneal cavity (basically holds the gut in place while the rest of the embryo moves)
How are the peritoneal and pericardial cavities separated from each other?
How are the pleural and pericardial cavities separated from each other?
Pleuroperitoneal folds grow and cover the pericardioperitoneal canals
Primordial lungs from the respiratory diverticulum grows laterally. The pleural cavity expands with it and its growth pushes the pericardial cavity forward and allows it to fuse together. Pleuropericardial folds push medially and fuse, closing both cavities off.
Pleuropericardial folds are located on which end and separates?
Pleuroperitoneal folds are located on which end and separates?
- cranial, heart and lungs
- caudal, lungs from GI
Describe how the pleuropericardial folds develop:
They project inward to form membranes that grow into the canals and form separations between heart and lungs
Briefly describe how the lungs develop
Bronchial buds grow into the canals ventrally and expands to form the pleural cavity, while pushing the pericardial cavity ventrally
Bronchial bud growth splits the mesenchyme into…
Outer layer - thoracic wall
Inner layer - fibrous pericardium
What happens to pleuroperitoneal membranes? When does this happen?
- Fuses with the dorsal mesentary and septum tranvsersum, separates the lungs and the GI
- Week 6
What forms the diaphragm?
Septum transversum, dorsal mesentery and pleuroperitoneal membranes fuse to form the diaphragm
What part of the diaphragm do each of these form?
Septum transversum
Dorsal mesentery
Myoblasts
central tendon
Median diaphragm
Crura of the diaphragm
Why is the innervation of the diaphragm (phrenic n.) originate in the cervical region?
It forms at C1-3 initially but is repositioned during development when myoblasts pull the ventral rami downward
Congenital diaphragmatic hernia (CDH)
Cause
Clinical
- (usually) L canal doesn’t close so pleural and peritoneal cavities are not separated
- viscera bulges up into the chest cavity and affect development of lungs. Polyhydramnios (excess amniotic fluid) may be present
