Midgut Anatomy Flashcards
What are the two organs of the midgut?
- small intestine: (Distal 1/2 of the duodenum, jejunum, ileum)
- Two thirds of the large intestine: (Cecum, appendix, ascending colon, transverse colon
Is the transverse colon anterior or posterior?
Anterior; it can be seen from an anterior view of the stomach without the greater omentum removed.
When you open the abdominal wall, what cavity are you peering into?
peritoneal cavity
When you open the abdominal wall, what sac are you peering into? Greater or lesser?
Greater sac
In order to view the last portion of the duodenum, what portions of the small intestine need to be removed?
Jejunum and ileum
Which trunk of the aorta serves the midgut?
Superior mesenteric artery
What plexus innervates the organs of the midgut?
superior mesenteric plexus (pre-aortic plexus)
What are the most anterior structures of the midgut?
- transverse colon
- jejunum
- ileum
The ascending colon is (anterior/posterior).
posterior; however sometimes the ileum and jejunum are found behind the ascending colon
The duodenum is (anterior/posterior) to the jejunum and ileum.
posterior
What organ of the midgut is just anterior to the aorta and the inferior vena cava?
Duodenum
What other organ is snuggled in the curvature of the duodenum?
pancreas
On an axial CT or MRI image through an approximate L3, list the location of the midgut organs from most posterior to most anterior.
Anterior: Transverse colon, ileum, jejunum, ascending colon, duodenum
What is the name of the ligament that secures the duodenum to the esophagus?
suspensory ligament
When the suspensory ligament is covered by peritoneum, what structure does it form?
the Ligament of Treitz
The majority of the duodenum is retroperitorneal/peritoneal?
Retroperitoneal; only parts 2 and 3 have peritoneum draping over the organ. It is not surrounded.
Which mesentery attaches the ileum and jejunum to the posterior abdominal wall?
The Mesentery
Are the jejunum and ileum peritoneal or retroperitoneal?
Both are peritoneal; they are completely covered by peritoneum and attached to the posterior abdominal wall by The Mesentery.
Which is slightly larger in caliber (diameter), the jejunum or the ileum?
The jejunum has a slightly larger caliber.
Which is longer the jejunum or ileum?
the ileum (14ft long), the jejunum is only 9ft long.
Which has more folds, the jejunum or ileum?
Jejunum
List differences between the jejunum and ileum.
Ileum:
- Longer (12 ft)
- smaller caliber
- less folds
- shorter vasa recta
- less metabolic activity
Which has longer straight vasa recta, the jejunum or the ileum?
Jejunum
Which portion of the small intestine has higher metabolic activity?
Jejunum, thus it has more folds to increase absorptive surface and a more direct artery supply.
What valve connects the ileum to the cecum?
ileocecal valve in the ileocecal junction, formed by the ileocecal sphincter.
Is the cecum peritoneal or retroperitoneal?
The cecum is completely covered by peritoneum and is thus peritoneal.
Where is the appendix?
It hangs from the cecum.
What is the lymphoid structure that hangs from the cecum?
appendix
Is the appendix retroperitoneal or peritoneal?
peritoneal; it is completely surrounded and is supplied by the mesoappendix.
Why do patients with appendicitis usually experience pain in dermatome T10?
referred pain
Can the appendix be found in multiple places?
Yes, the appendix can be found in multiple positions with respect to the cecum. The most common are retrocecal and pelvic.
What is the name of the junction between the ascending colon and the transverse colon?
The hepatic flexure or right colic flexure
What is the function of haustrum (pl: haustra)?
sacculation
What are epiploic appendages?
small sacs filled with fat; they are for fat storage
What type of muscle is tenia coli, where would you find them in the body?
smooth muscle thickenings, found on the surface of the colon as longitudinal ribbons
How is the transverse colon attached to the posterior abdominal wall?
by its mesentery, the transverse mesocolon
Is the ascending colon peritoneal or retroperitoneal?
retroperitoneal
Is the transverse colon peritoneal or retroperitoneal?
peritoneal
Retroperitoneal or peritoneal?
- Cecum
- Ascending colon
Cecum: peritoneal; the peritoneum covering the ileum completely covers the cecum
Ascending colon: retroperitoneal; the peritoneum is draped on the top, but does not cover this structure.
What 3 additional features distinguish the colon from the small intestine?
- tenia coli
- epiploic appendages
- haustrum
The aorta has 3 major unpaired trunks. Name them.
- Celiac trunk
- Superior Mesenteric Artery
- Inferior Mesenteric Artery
List the major branches of the superior mesenteric artery.
- intestinal branches (12-18)
- middle colic artery
- ileocecal artery
- Right colic artery
What portion of the large intestine does the middle colic artery serve?
Transverse colon
What portion of the small intestine do the intestinal branches serve?
the jejunum and ileum
What portion of the large intestine does the ileocecal artery serve?
ileocolic region
What 3 structures or regions are served by the right colic artery?
- ascending colon
- hepatic flexure
- transverse colon
The beginning of the superior mesenteric artery is posterior to what organ?
pancreas
To gain access to the superior mesenteric artery during surgery what structures would you have to cut through using an anterior abdominal approach?
- skin
- Abdominal wall muscles
- parietal peritoneum
- Stomach
- pancreas
6 finally the SMA
What two blood vessels “sandwich” the duodenum?
- superior mesenteric artery
2. aorta
If you had to use an anterior approach to access the superior mesenteric artery, list the organs you would pierce.
SAPSPS
- skin
- abdominal wall muscles
- Parietal peritoneum-peritoneal cavity-visceral peritoneum
- stomach
- pancreas
- SMA
The portal vein is formed by the combination of which two veins?
- splenic vein
2. superior mesenteric vein
Which is a tributary to the IVC, (portal vein/hepatic vein/superior mesenteric artery)
the hepatic vein is a tributary to the IVC. Blood from the gut enters the portal vein & travels through the liver to the hepatic veins which are tributaries to the IVC.
What organ is found immediately anterior to the SMA at the point where it branches from the aorta?
pancreas
The SMA projects slightly anteriorly, from its root on the aorta. When we see it emerging anteriorly, it is between which two organs?
pancreas and the duodenum
What is the name of the smaller ganglia flanking the superior mesenteric ganglion?
aorticorenal ganglia
What type of fibers might you find in the superior mesenteric artery?
- motor fibers carrying movement orders from the CNS to the organ
1a. para/pre from vagus
1b. symp/pre from thoracic & lumbar splanchnic
1c. symp/post - sensory fibers carrying sensor stimuli from the organ to the CNS
List the verterbral levels in which you would find cell bodies of thoracic splanchic nerves.
T5-T12
Describe the sympathetic preganglionic fibers that form the (1) greater thoracic splanchnic nerve (2) lesser thoracic splanchnic nerve & (3) least thoracic splanchnic nerve.
- Greater thoracic splanchnic nerve is formed by T5-T9
- Lesser thoracic splanchnic nerve is formed by T10-T11
- Least thoracic splanchnic nerve is formed by T12
How and where do vagal fibers enter into the abdomen?
The right and left vagal trunks enter the abdomen with the esophagus at vertebral level T10.
Where are all of the cell bodies of preganglionic sympathetic neurons located? (in terms of sympathetic innervation)
T5-L2
Describe the location of the intermesenteric plexus.
In between the two mesenteric arteries; also in between the two mesenteric plexuses.
What fibers might you find in the intermesenteric plexus?
- mostly sympathetic pre and post ganglionic fibers
2. some mini tiny ganglia where symp/pre fibers synapse instead of synapsing in the IMA or SMA
