Chapter 7 - The Gut Tube and the Body Cavities Flashcards
What happens with the ventral layer (endoderm) during the 3rd and 4th week?
The endoderm rolls down to form the gut tube.
What happens during the 3rd and 4th week with the neural tube?
The top layer (ectoderm) of the trilaminar embryonic disk forms the neural plate that rolls up into a tube to form the brain and the spinal cord by the process called neurulation.
Which tube is dorsally?
The neural tube
Which tube is ventrally?
The gut tube
What holds the two tubes together?
The middle layer (mesoderm)
What happens with the lateral plate component of the mesoderm during the 3rd and the 4th week?
The lateral plate component spilts into:
- Visceral (splanchnic) layer
- Parital (somatic) layer
Which tube is the visceral layer intimately connected to?
The gut tube
Lateral body wall folds (one on each isde of the embryo)?
Formed by the parietal layer, together with the overlying ectoderm
Primitive body cavity
- The space between the visceral and the parietal layers of lateral plate mesoderm
- at this early stage it is a continous cavity, since it has not yet been subdivided into the pericardial, pleural, and abdominopelvic regions.
When does the intraembryonic mesoderm differentiate into paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm?
At the end of the 3rd week
Paraxial mesoderm
- Forms somitomers and somites that play a major role in forming the skull and vertebrae
Intermediat mesoderm
- Contributes to the urogenital system
Lateral plate mesoderm
- Is involved in forming the body caivty
Parietal (Somatic) layer
- Is adjacent to the surface ectoderm and continouos with the extraembryonic parietal mesoderm layer over the amnion.
- Parietal (somatic) layer of the lateral plate mesoderm + overlying ectoderm = somatopleure
Somatopleure =
Parietal (somatic) layer of the lateral plate mesoderm + overlying ectoderm
Visceral (splanchnic) layer
- Is adjacent to endoderm forming the gut tube and continuous with the visceral layer of extraembryonic mesoderm covering the yolk sac.
- The visceral (splanchnic) layer of lateral plate mesoderm + underlying endoderm = splanchnopleure.
Splachnopleure =
The visceral (splanchnic) layer of lateral plate mesoderm + underlying endoderm
When is the lateral body wall folds formed?
During the 4th week
What does the lateral body wall folds consist of?
It consist of the parietak layer of lateral plate mesoderm, ovelrying ectoderm, and cells from adjacent somites that migrate into the mesoderm layer across the lateral somitic frontier.
How does the gut tube form?
The gut tube forms when the endoderm layer fold ventrally and closes
What happens with the lateral body wall folds at the end of the 4th week?
A closure happens at the end of the 4th week, when the lateral body wall folds meet in the midline and fuse to close the ventral body wall
When does the embryo curve into the fetal position?
At the end of the 4th week
The closure of the ventral body wall is complete exept…
in the region of the connecting stalk (future umbilical cord)
Closure of the gut tube is complete exept…
for a connection from the midgut region to the yolk sac called the vitelline (yolk sac) duct
When does the vitelline (yolk sac) duct degenerate with the yolk sac?
between the 2nd and 3rd months of gestation
What forms the parietal layer of the serous membranes lining the outside of the perioteal, pleural, and pericardial cavities?
Some cells of the parietal layer of lateral mesoderm lining the body wall of the primitive embryonic cavity become mesothelial and forms the parietal layer of the serous membranes lining the outside of the perioteal, pleural, and pericardial cavities.
What covers the abdominal organs, lungs and heart?
Some cells of the visceral layer of lateral plate mesoderm form the visceral layer of the serous membranes covering the abdominal organs, lungs and heart
Dorsal mesentery
- Visceral and parietal layers are contiuous with each other as the dorsal mesentery
- Suspends the gut tube from the posterior wall into the peritoneal cavity.
- Extends continuously from the caudal limit of the foregut to the end of the hindgut
Ventral mesentery
Exists only from the caudal foregut to teh upper portion of the duodenum and results from thinning mesoderm of the septum transversarum
Septum transversarum
- A block of mesoderm that forms connective tissue in the liver and the central tendon of the diaphragm
- Is a thick plate of mesodermal tissue occupying the space between the thoracic cavity and the stalk of the yolk sac
Peritoneum
- Provide a pathway for blood vessles, nerves, and lymphatics to the organs
- The mesenteries are double layers of peritoneum
Where is the Septum transversarum derived from?
Septum transversarum derive from the visceral (splanchnic) mesoderm surrounding the heart and assumes its position between the primitive thoracic and abdominal cavities when the cranial end of the embryo grows and curves into fetal postion.
Does the Septum transversarum separate the throacic and abdominal completely?
No, because they have large openings, the pericardioperitoneal canals, on each side of the foregut.
Ventral and lateral expansion is posterior to…
the pleuropericardial folds
With expansion of the lungs, mesoderm of the body wall splits into two components:
- The definitive wall of the thorax
- The pleurocardial membranes, which are extentions of pleuropericardial folds that contains the common cardinal veins and phrenic nerves
The thoracic cavity is divided into:
- The definitive pericardial cavity
2. Two pleural cavities
What does the pleuropericardial membranes form in adults?
It forms the fibrous pericardium
Are the pleural cavities separate from the pericardial cavities?
Yes, but they remain in open communication with the abdominal (perioteneal) cavity by wya of the pericardioperitoneal canals.
When does the pleuroperitoneal folds fuse with the mesentery of the esophagus and with the septum transversarum?
By 7th week
The connection between the pleural and peritoneal portions of the body cavity is closed by….
the pleuroperitoneal membranes
What penetrates the pleuroperitoneal membranes to form the muscular part of the diaphragm?
the myoblasts originating from somites at cervical segments three to five (C3-5)
Superior vena cava develops from…
the right common cardinal vein
the common cardinal vein and the phrenic nerve can be found in…
the pluropericardial membranes
The diaphragm is derived from the following structures:
● The septum transversum, which forms the central tendon of the diaphragm
● The two pleuroperitoneal membranes
● Muscular components from somites at cervical segments three to five
● The mesentery of the esophagus, in which the crura of the diaphragm develop
What happens with the septum transversum and the nerve components C3-C5 during the 4th week?
- the septum transversum lies opposite cervical somites
- The nerve components of C3-C5 of the spinal cord grows into the septum.
The phrenic nerve pass into the septum through the….
pleuropericardial folds
The phrenic nerve innervates the diaphragm into…
the fibrous pericardium
What cause the repositioning of the diaohragm?
The rapid growth of the dorsal part of the embryo (vertebral column), compared with that of the ventral part
When does some of the dorsal bands of the diaphragm originate at the level of the first lumbar vertebra?
By the beginning of the third month
How does the phrenic nerve supply the diaphragm?
I supplies its motor and sensory innervation
Where is the peripheral part of the diaphragm derived from?
Mesenchyme of the throacic wall
Some of the lower intercostan (thoracic) nerves contribute…
sensory fibers to the peripheral part of the diaphragm
