Intestines and the Portal-Systemic Anastomoses Flashcards
The pylorus empties the contents of the stomach into the:
Duodenum (first part of the small intestine)
Where does most of the absorption occur in the GI tract?
In the small intestine - its length varies, but averages 6-7 meters. Excision of up to one third of it is compatible with a fairly normal lifestyle
Where is the small intestine located?
Behind (posterior) the greater omentum and is connected to the vertebral column by the mesentery, which is the double-layered peritoneum that encloses both the jejunum and ileum and attaches them to the posterior abdominal wall
Where does the jejunum begin and course?
Begins at the duodeno-jejunal flexure and is about 2/5 of the entire small intestine.
Both the jejunum and the ileum are greatly coiled and are covered by the:
Greater omentum. There is no clear line of demarcation between the jejunum and ileum
How do we tell the jejunum and ileum apart?
The beginning of the jejunum and the end of the ileum have distinct morphological characteristics
Describe the musculature of the jejunum:
- It has a wider (larger) diameter with thicker walls.
- It has both longitudinal (superficial) and circular (deep) muscle layers
- Its lumen has numerous circular folds (plicae circulares) that can be felt thru the wall of the jejunum
What is the purpose of the circular folds in the jejunum?
THey greatly increase the surface area for absorption
What is distinct about the mesentery connecting the jejunum to the vertebrae?
Relatively fat free and therefore transparent in the living body
What is the arterial supply to the jejunum supplied by?
The jejunal branches of the superior mesenteric artery.
Where do the jejunal branches arise from?
The left side of the superior mesenteric artery and pass between the two layers of the mesentery to form arterial loops
Where do the vasa recta (straight vessels) arise from?
The arterial loops (arcade) and pass to the jejunum. These straight arteries are longer than those of the ileum and they do not anastomose within the mesentery.
Do the vasa recta anastomose?
They pass to the alternate sides of the jejunum and anastomose extensively within the jejunum
Where is the venous drainage of the jejunum?
To the superior mesenteric vein which parallels the SMA. The SMA joins the hepatic portal vein
Describe lymphatic drainage of the jejunum (and ileum):
It is extensive for both. Lymphatics of the small intestine are called LACTEALS. Dissolved fats give the lymphatic fluid a milk-like appearance.
Lymphatic vessels pass into the mesentery and drain into:
The mesenteric lymph nodes which are located near the intestinal wall, along the arterial arcades and the proximal part of the SMA
All lymph nodes ultimately drain into the:
Superior mesenteric nodes
Describe the ileum:
- It is the portion of the intestine between the jejunum and the ileocecal valvle
- It is the distal 3/5 of the small intestine distal to the duodenum
What regions of the abdominal cavity does the ileum occupy?
The hypogastric and inguinal region. Its terminal part usually occupies the pelvis minor
What are Peyer’s patches?
Aggregated lymph nodes are abundant in the ileum. They are longer and more numerous than those of the jejunum.
Describe the musculature of the ileum:
- The diameter is narrower and its walls are thinner and less vascular than those of the jejunum
- It has both longitudinal and circular layers but the circular folds decrease in size and number proximal to distal and are entirely absent in is terminal part
Describe the mesentery enclosing the ileum:
- It has abundant fat and therefore less transparent than that of the jejunum. The jejunum and ileum are attached to the posterior abdominal wall by an extensive fold of peritoneum, the mesentery, which allows free motion so that each intestinal coil can accommodate itself to changes in form and position
What lies between the two layers of mesentery?
Blood vessels, nerves, lacteals, and variable amounts of fat
Arterial supply of the ileum is provided by:
Ileal branches from the SMA. These ileal branches form complex arcades within the mesentery and straight arteries (vasa recta) supply the ileum.
Are the vasa recta shorter in the ileum or the jejunum?
Vasa recta of the ileum are shorter than those of the jejunum
The venous drainage of the jejunum is accomplished via:
The superior mesenteric vein, which then joins the splenic vein to form the hepatic portal vein
Describe the innervation of the small intestine:
- Supplied by autonomic and sensory fibers from the celiac and superior mesenteric plexuses
- These fibers accompany arteries to the small intestine
- These sensory fibers include both pain fibers and fibers concerned with the reflex regulation of food movement and secretion
What is the small intestine sensitive to?
Distention, not pain (including cutting and burning?)
The large intestine is between:
The cecum and rectum
Defining characteristics of the colon:
- Large diameter
- Thin walls
- Three thickened bands of longitudinal muscle - TAENIA COLI
- The sacculations of its wall between the taenia, called HAUSTRA
- Small pouches of omentum (peritoneum) filled with fat - OMENTAL APPENDICES
What is the taenia coli?
Three bands of outer longitudinal muscle layers, spaced approximately 12 mm apart
The mesocolic taenia is related to:
The transverse mesocolon
The omental taenia is related to:
The greater omentum
The free taenia is related to:
Nothing in particular
Where are the taenia coli most prominent?
In the cecum and ascending colon
What are the epiploic appendices?
Pendular pockets of fat enclosed within the peritoneum and extend from the wall of the colon
What are haustra?
They are sacculations due to the circular muscles, important for the movement of intestinal content. Some believe they are formed by the shortness of the taenia compared to the length of the colon. It is possible that both circular muscles and taenia participate in the formation of haustra
Is the cecum peritoneal or retroperitoneal?
It is completely enclosed in peritoneum and is peritoneal.
Describe the cecum:
- First part of the large intestine
- Continuous with the ascending colon
- Ileum opens into its superior part
- Broad blind pouch 5-7 cm in length
- Located in the right lower quadrant
The ileum enters the cecum obliquely and forms the:
Ileocecal valve, although it has little sphincter activities due to poorly developed circular muscles
What is the purpose of the ileocecal valve?
Prevents excessive reflux of fecal materials back into the ileum
Describe the route of the ascending colon:
It ascends on the right side of the abdominal cavity from the cecum to the right lobe of the liver, where it turns to the left as the right colic (hepatic) flexure
Does the ascending colon have a mesentery?
No, it lies retroperitoneally along the right side of the posterior abdominal wall
Describe the route of the transverse colon:
- It hangs down as a loop to a variable extent
- It is the largest and most mobile part of the large intestine
- Crosses the abdomen from the right colic flexure to the left colic flexure, where it bends inferiorly to become the descending colon
The mesentery of the transverse colon is:
The transverse mesocolon - a peritoneal structure
Describe the route of the descending colon:
Descends from the left colic (splenic) flexure into the left iliac fossa, where it is continuous with the sigmoid colon
Does the descending colon have a mesentery?
No, it is therefore retroperitoneal
Describe the route of the sigmoid colon:
- Located between the descending colon and rectum
- Extends from the pelvic brim to the 3rd segment of the sacrum, where it becomes the rectum
- Termination of the taenia coli indicateds the beginning of the rectum
- Has long mesentery (sigmoid mesocolon) and has considerable freedom of movement
- Monetal appendages are very long and filled with fat
What is stored in the sigmoid colon?
Feces until just before defecation
What is the cecum and appendix innervated by?
Nerve fibers derived from the celiac and superior mesenteric ganglia
What is the ascending colon innervated by?
Nerve fibers from the celiac and superior mesenteric ganglia
What is the transverse colon innervated by?
Fibers originating from the superior mesenteric plexus
What is the descending colon innervated by?
Nerve fibers derived from the lumbar part of the sympathetic trunk and the superior hypogastric plexus
What is the sigmoid colon innervated by?
Nerve fibers derived from the superior hypogastric plexus and the pelvic splanchnic nerves
Where is the superior mesenteric artery?
It is the second unpaired branch of the abdominal aorta, located at the level of L1 and is situated posterior to the pancreas
Where is the right colic artery and what does it supply?
This branch of the SMA supplies the ascending colon. It generally bifurcates into ascending and descending branches
The descending branch of the right colic artery anastomoses with a branch of:
The ileocolic artery
What is the ileocolic artery and what does it supply?
This branch of the SMA supplies parts of the ileum, cecum, and appendix
A. The ascending colic artery supplies the:
Ascending colon
B. The anterior cecal artery supplies the:
Anterior cecum
C. The posterior cecal artery supplies the:
Posterior cecum
D. Appendicular artery supplies the:
Appendix
The ileal branch supplies the:
Distal ileum
What is the middle colic artery and what does it supply?
- This is the main artery of the transverse colon.
- It bifurcates into right and left branches
- The right branch anastomoses with ascending branches of the right colic artery
- The left branch anastomoses with ascending branches of the left colic artery
What is the inferior mesenteric artery and what does it supply?
- It is the third upaired artery of the abdominal aorta
- Arises at the level of L3 and the inferior border of the duodenum
- Supplies the descending and sigmoid colon
Describe the left colic artery:
This artery bifurcates into an ascending and descending branch. The ascending branch anastomoses with the middle colic artery
Describe the sigmoid artery:
This division of the IMA gives mutliple branches, some may anastomose with the descending left colic arter;y
What does the superior rectal artery supply?
This distal continuation of the IMA supplies the arterial blood to the rectum
What does the marginal artery result from?
The anastomoses of the branches of the ileocolic, right , middle, and left colic arteries. If the marginal artery is well-developed, a surgeon can tie off a local artery to a segment of the colon and the region will still be serviced since the marginal artery will carry blood around the clamp
The hepatic portal vein is formed by the union of:
3 veins - splenic, superior mesenteric and inferior mesenteric
Where does the portal vein collect blood from?
The abdominal part of the GI tract, the gall bladder, pancreas, and spleen
Where does the portal vein carry the blood to?
Carries it to the liver where the venous blood is collected by the hepatic veins which drain into the inferior vena cava
What is a portal system?
Two capillary beds connected by a vein.
What is the function of the portal system?
To deliver blood rich in nutrients from the intestine to the liver
Describe the portal-systemic anastomoses:
The portal venous system communicates with the systemic venous system in several location. When the portal circulation is obstructed, blood from the GI tract can still reach the heart thru the inferior vena cava via a number of collateral routs.
Does the portal vein have valves?
The portal vein and its tributaries have no valves, so the blood can flow from the damaged liver to the inferior vena cava via alternate routes
What happens in the gastro-esophageal area?
The esophageal tributaries of the left gastric vein (portal) anastomose with the esophageal vein, which empties into the azygos (systemic) vein
What happens in the ano-rectal region?
The superior rectal vein (portal) anastomoses with the middle and inferior rectal veins (systemic), the latter are tributaries of the internal iliac and internal pudendal veins
What happens in the paraumbilical region?
The paraumbilical veins anastomose with veins in the anterior abdominal wall - lateral circumflex iliac, abdominal epigastric veins
What happens with cirrhosis of the liver?
Patients sustain progressive destruction of hepatic parenchymal cells which are replaced with fibrous tissue, causing obstruction of venous blood flow which could result in portal hypertension. When portal venous blood is not allowed to drain into the inferior vena cava, it is diverted to the systemic veins
What are varicose veins?
When portal venous blood is not allowed to drain into the inferior vena cava, it is diverted to the systemic veins The blood diverted to system veins causes enlargement of the veins
Varicose veins in the anal region are:
Hemorrhoids
Varicose veins in the gastro-esophagel regions are:
Esophageal varices
Varicose veins in the umbilical area are:
Caput medussa.
What is the significance of enlarged varicose veins?
They could rupture and cause severe bleeding
