TBL 17 Flashcards
What are mesentries? What is the dorsal mesentery?
Mesenteries are formed at the sites of continuity between the parietal and visceral peritonea.
The gut tube is suspended from the dorsal (posterior) wall by the dorsal mesentery and the mesentery extends from the abdominal portion of the esophagus to the end of the hindgut.
What is the septum transversum derived from? What derives from the septum transversum?
Visceral mesoderm that surrounds the heart tube.
The ventral mesentry is derived from the septum transversum. It connects the abdominal part of the esophagus, the stomach and proximal duodenum to the ventral (anterior) body wall.
What is the liver bud?
It is an endodermal outgrowth from the proximal duodenum, which grows into the septum transversum.
What forms the falciform ligament and lesser omentum?
The growth of the liver within the septum transversum separates the ventral mesentery into the falciform ligament and lesser omentum. The septum transversum goes on to become the central tendon of the diaphragm.
What suspends the fusiform stomach from the dorsal body wall?
Dorsal mesogastrium which is a portion of the dorsal mesentery associated with the stomach
Describe the rotation of the fusiform stomach.
The fusiform stomach rotates 90 degress clockwise around its longitudinal axis, which causes the left side to face anteriorly and its right side to face posteriorly.
During the rotation, the original posterior wall grows faster than the original anterior wall creating the greater and lesser curvatures of the stomach.
What does additional rotation of the stomach around the anteroposterior do?
It move the distal part of the stomach to the right and upward and its proximal part to the left and downward. The rotation pulls the duodenum to the right creating its C-shaped loop.
It also causes the dorsal mesogastruum to bulde downward from the greater curvature as the double layered greater omentum. The descending portion of the looping greater omentum fuses with the ascending portion to create its four-layered structure.
Where do the primoridia of the pancreas and spleen originally reside?
pancreas: dorsal mesentery
spleen: dorsal mesogastrium
What does stomach rotation do to the mesenteries?
The stomach rotations pull the mesenteries to the left where the dorsal mesentery partially fuses with the parietal peritoneum of the posterior body wall and places the pancreas in its retroperitoneal location.
What does the dorsal mesogastrium do?
It encloses the spleen as visceral peritoneum and creates the gastrosplenic ligament that connects the stomach to the spleen.
What does the non-fused portion of the dorsal mesentery form?
It forms the splenorenal ligament that connects the spleen to the body wall in the region of the retroperitoneal left kidney.
What does the esophageal mucosa consist of?
richly vascular lamina propia covered by non-keratinized stratified squamous epithelium
At the esophagogastric junction, what happens to the nonkeratinzed stratified squamous epithelium? What is this change’s clinical relevance?
The nonkeratinized squamous epithelium abruptly changes to simple columnar epithelium as the esophagogastric junction. This serrated border (called the Z line) is important because it is the most common site of esophageal carcinomas.
What is Barrett’s esophagus and what is the likelihood of its transformation into an adenocarcinoma?
It is metaplasia of the esophageal epithelium which means that the stratified squamous epithelium is replaced by the columnar epithelium. This can happen anywhere above the gastroesophageal junction. It may rarely lead to the more serious adenocarcinoma.
What is the most common cause of esophagitis and what conditions are typically associated with the causation?
Inflammation of the esophagus with damage to the epithelium is called esophagitis. Its most common cause is reflux of gastric contents into the lower esophagus, which impairs reparative capacity of esophageal mucosa.
Conditions:
Gastroesphageal reflux disease
Hiatal hernia
What is the muscularis mucosae?
It is a longitudinal layer of smooth muscle which separates the mucosa and submucosa. This muscle layer is present along the entire GI tract. Periodic contractions of the muscularis mucosae creates the folding of the mucosa to assist peristaltic propulsion.
What does the submucosa of the esophagus do?
It seperates the muscularis mucosae and muscularis externa
It also has secretory acini that secrete mucus into ducts that open into the esophageal lumen to lubricate the apical surface of the lining epithelium.
What is the muscularis externa of the esophagus?
It consists of inner circular smooth and outer longitudinal skeletal muscle layers. Skeletal muscle is present in the outer layer in the proximal 1/3 of the esophagus and smooth muscle composes both layers in the distal 2/3.
Where is the adventitia of the esophagus located? What is it composed of?
It is located external to the muscularis externa and consists of loose connective tissue without a covering mesothelium. (Only the short abdominal portion of the esophagus is intraperitoneal and enclosed by visceral peritoneum).
Why is esophaeal adenocarcinoma associated with rapid tumor cell metastasis outside the esophageal boundaries?
The lack of serosa along most of the esophageal length may account for the rapid spread of metastatic tumor cells outside esophageal boundaries.
What arteries supply the esophagus?
The left gastric artery supplies the abdominal part of the esophagus and branches of the descending aorta supply the thoracic part.
What is the orders of the layers of esophagus?
FROM OUTSIDE TO INSIDE:
Mucosa –> muscularis mucosae –> subcomusa –> muscularis externa –> adventia
