Intestine & Portal System Flashcards
How much of the small intestine can be removed while preserving a normal life?
Up to 1/3
What is the mesentery?
A double-layered visceral peritoneum that splits to enclose both the jejunum and ileum and attaches to the posterior abdominal wall.
How long is the jejunum? Where does it change to ileum?
About 2/5 of small intestine which is 6-7m long. There is no clear line of demarcation between jejunum and ileum as the morphological character of the intestine changes gradually.
What covers the jejunum and ileum?
Aside from the visceral peritoneum, the flap of the greater omentum covers it.
What do duodenum and jejunum mean?
Duodenum = 12 fingerbreaths, it is the length of 12 finger breadths Jejunum = empty
What is the structure of the musculature of the jejunum?
It has a wider diameter with thicker wall.
Superficial muscle layer - longitudinal
Deep muscle layer - circular
Lumen has numerous circular folds which greatly increase the surface area for absorption
What are the circular folds of the jejunum which increase surface area called?
Plicae circulares
What is the characteristic of jejunal mesentery?
Relatively fat free and therefore transparent in living body, so blood vessels can easily be seen.
Where is the jejunum?
Starts at duodeno-jejunal flexure and is mostly located near the umbilical region of the abdomen
What is the arterial supply to the jejunum?
Jejunal branches, which arise from the left side of the superior mesenteric artery. They pass between the two layers of mesentery and form arterial loops, which give off the vasa recta and pass blood to the jejunum
What are the vasa recta of the jejunum? How do they compare to the ileum’s branches?
Straight arteries which come off the arterial loops / arcade of the jejunal branches of the SMA.
They are longer than those of the ileum and do not anastomose within the mesentery, but do so extensively within the jejunum
What is the venous drainage of the jejunum?
Superior mesenteric vein, which parallels superior mesenteric artery. It will drain into the hepatic portal vein
What are lymphatics of the small intestine called and why?
Lacteals - dissolved fats give the lymphatic fluid a milk-like appearance.
How does lymph fluid from the small intestines drain?
Lymph vessels pass into the mesentery and drain into mesenteric lymph nodes located near the intestinal wall, arterial arcades, and proximal SMA.
They will all drain into the superior mesenteric lymph nodes, which drain into cisterna chyli
Where does the ileum run and how much of the intestine does it make up?
Between the jejunum and the ileocecal valve, it is the distal 3/5 of the small intestine. It occupies the hypogastric and inguinal region of the abdominal cavity, and is in the pelvis minor.
What are Peyer’s patches?
Aggregated lymphatic tissues that are more numerous along the ileum
How do you describe the musculature of the ileum?
It is narrower, its walls are thinner and less vascular than those of the jejunum. It has both longitudinal and circular muscle layers, but the circular folds decrease in size and number throughout are entirely absent in the terminal part.
How does the mesentery of the ileum differ from the jejunum?
Ileum has abundant fat in its mesentery and is therefore less transparent than the jejunum.
What is the vascular supply of the ileum?
Vasa recta which are shorter than those of the jejunum. Vasa recta arise from arterial arcades of ileal branches of SMA.
What is the venous drainage of the ileum?
By the superior mesenteric vein, same as jejunum.
What is the innervation of the small intestine provided by? Where do the fibers run?
Celiac and superior mesenteric plexuses.
The fibers run with the arteries within the mesentery, and will be autonomic (motor) or sensory
What types of sensory innervation is in the small intestine?
Mainly sensitive to distention. However, there are pain fibers and fibers which sense food and control peristalsis?
Where does the large intestine run?
Between the cecum and the rectum. It is about 1.5m long, if you include the sigmoid colon and rectum
What are the characteristics of the large intestine?
Large diameter, thin walls, thickened bands of longitudinal muscle called Taenia coli, sacculations of the wall called haustra, and small pouches of peritoneum filled with fat called omental appendices.
What are taenia coli? What are its three parts?
Three bands of longitudinal smooth muscles on the outside of the colon which are most prominent in cecum and ascending colon.
Mesocolic taenia - related to transverse mesocolon
Omental taenia - related to greater omentum
Free taenia - not related to any structure
What are the epiploic appendices of the colon?
Small pouches of (omentum) peritoneum filled with fat, also called omental appendices. They are pendular pockets of fat enclosed within the peritoneum extending from the walls of the colon
What are haustra?
Sacculations due to circular muscles, may be produced by taenia as well since the taenia are short compared to the length of the colon
Is the cecum peritoneal or retroperitoneal? Where does the ileum open into it and what is it continuous with?
It is completely enclosed in peritoneum and is thus a peritoneal structure.
The ileum opens into this sac-like portion in its superior part
It is continuous with the ascending colon, located in right lower quadrant
What is the ileocecal valve? What is its function?
Valve between ileum and cecum, which has poorly developed circular muscles and does not act as a great sphincter. However, it prevents excessive reflux of fecal material back into the ileum
What are the four parts of the colon and are they peritoneal or retroperitoneal?
- Ascending colon - retroperitoneal
- Transverse colon - peritoneal
- Descending colon - retroperitoneal
- Sigmoid colon - peritoneal
What is the ascending colon and where does it connect to the transverse mesocolon?
Ascends on right side from the cecum to the right lobe of the liver. Turns to the left as the right colic (hepatic) flexure.
What is the transverse colon and what holds it up?
Largest and most mobile segment of large intestine, crosses abdomen at right colic flexure to left colic flexure.
It is held up by a mesentery called the transverse mesocolon.
What is the descending colon and where does it connect to the transverse colon?
Part of colon from transverse colon to sigmoid colon, at the left iliac fossa
It connects to the transverse colon at the left colic flexure
Where does the sigmoid colon extend? What is its function?
From the pelvic brim (left iliac fossa, from descending colon) to the 3rd segment of the sacrum, where it becomes the rectum.
Feces are stored in this part of the colon until just before defecation.
What marks the beginning of the rectum?
The termination of the taenia coli on the sigmoid colon
What holds up the sigmoid colon?
A long mesentery called the sigmoid mesocolon. It has a considerable freedom of movement
What is distinctive of the wall of the sigmoid colon?
Long omental appendages which are filled with fat.
What parts of the large intestine do the celiac & superior mesenteric ganglia innervate?
Cecum & appendix, ascending colon are innervated by both
What part of the large intestine is innervated by the superior mesenteric plexus?
Transverse colon
What innervates the descending colon?
Lumbar part of sympathetic trunk, superior hypogastric plexus
What innervates the sigmoid colon?
Superior hypogastric plexus, and pelvic splanchnic nerves
What are the primary arteries of the colon?
- Superior mesenteric artery
- Right colic artery - from SMA
- Ileocolic artery - from SMA
- Middle colic artery - from SMA
- Left colic artery - from IMA
- Sigmoid artery - from IMA
- Superior rectal artery - from IMA
What is the superior mesenteric artery? What level is it at?
Second unpaired branch of abdominal aorta, located at the level of LV1. It is posterior to the pancreas.
What is the right colic artery and what does it branch into?
Branch of the superior mesenteric artery which supplies ascending colon. It generally has ascending and descending branch. Its descending branch often anastomoses with a branch of the ileocolic artery
What is the ileocolic artery and what are its branches?
Branch of superior mesenteric artery, supplies ileum, cecum, and appendix.
1. Ascending colic artery - anastomoses with right colic
2/3. Anterior & posterior cecal arteries - to cecum
4. Appendicular artery - to appendix
5. Ileal branch - to distal ileum
What is the middle colic artery and its main branches?
Main artery of transverse (middle) colon
- Right branch - will anastomose with ascending branch of right colic artery
- Left branch - Will anastomose with ascending branches of left colic artery
What is the inferior mesenteric artery?
The third unpaired branch of the abdominal aorta, arising at LV3 and the inferior border of the duodenum. It supplies mainly the descending and sigmoid colon
What are the branches of the inferior mesenteric artery to the large intestine? What are their branches?
- Left colic artery - bifurcates into ascending and descending. Ascending anastomoses with middle colic
- Sigmoid artery - Many branches, some anastomose with descending left colic
- Superior rectal artery - terminal branch of IMA, supplying rectum
What is the marginal artery? What is its significance?
A variant or “physiologic” artery that can form from the anastomoses of the branches of the ileocolic, right, middle, and left colic arteries.
A surgeon can clamp a local artery to the colon and it will still be supplied blood because of the marginal artery
What forms the portal vein?
Union of splenic, superior mesenteric, and inferior mesenteric veins.
Where do the hepatic veins drain?
Inferior vena cava
Why is it called the portal vein?
There are capillaries in the GI tract, gall bladder, pancreas, and spleen, and there are capillaries in the liver. Thus, it is a portal system
What is the significance of the portal vein having no valves?
During liver disease when blood becomes backed up in the liver / portal system, blood can enter the systemic circulation (inferior vena cava) by bypassing the portal system via a number of different routes
What are the three areas where portal blood can enter the systemic venous system during portal hypertension?
- Gastroesophageal area
- Anorectal area
- Paraumbilical area
What is the gastro-esophageal area?
Where esophageal tributaries of the left gastric vein (portal system) anastomose with the esophageal vein, which empties into the azygos vein (systemic).
What is the ano-rectal region?
Superior rectal vein of the portal system anastomoses with the middle and inferior rectal veins which are systemic.
The middle and inferior rectal veins are tributaries of the internal iliac and internal pudental veins
What is the paraumbilical region?
Where paraumbilical veins of the portal system anastomose with veins of the anterior abdominal wall (lateral circumflex iliac, abdominal epigastric) which are systemic
What is cirrhosis and what does it cause?
Disease of liver which causes progressive destruction of hepatic pernchymal cells, which are replaced by fibrous tissue. This can result in portal hypertension
What happens to the superficial veins during portal hypertension?
They are overflowing since blood cannot go directly to the IVC through the liver. Thus, they are called varicose veins
What are varicose veins in the anal region called?
Hemorrhoids
What are varicose veins in the gastroesophageal regions called?
Esophageal varices
What are varicose veins in the umbilical region called?
Caput medusa - from engorged superficial epigastric veins
What is the vermiform appendix? Is it peritoneal or retroperitoneal?
Blind-ended tube connected to cecum, usually in the retrocecal space. It has its own mesentery and is thus peritoneal.
It is a continuation of the longitudinal tinea often.
