1-7 Anatomy of the Infracolic Compartment Flashcards
What is the jejunoileum?
portion of the small intestine (jejunum and ileum) that connects the duodenum with the cecum of the colon
Why is the term jejunoileum used?
The common term jejunoileum is used because the transition from jejunum to
ileum is so gradual that their definitive structural differences are most easily observed by comparing their combined proximal and distal regions.
When comparing the jejunum to the ilium, what are the differences?
the jejunum has:
- Greater diameter
- Thicker wall
- Increased number of circular folds
- Few lymphoid nodules
- Increased vascularity
- Deeper color
- Less mesenteric fat
- Arterial arcades are fewer
- Vasa recta are long
What is the location of the jejunum?
Begins at the point of re-peritonealization of part IV of the duodenum on the left of LV2
Upper 1/3 of the jejunoileum located in the upper left quadrant
Middle 1/3 located in umbilical region
Lower 1/3 in pelvis and right iliac fossa
Also, most of the jejunum lies in the left upper quadrant, while most of the ileum resides in the lower right quadrant.
What does the terminal ileum have to do with the iliocecal junction? What are the spatial relationships involved?
Note: The terminal ileum ascends from the pelvis to become continuous with the right colon at the cecum (ileocecal junction).
What is the approximate length of the jejunoilium?
~20 feet
Upper 2/5 (8 ft.) is jejunum; lower 3/5 (12 ft.) is ileum
Why does the thickness of the intestinal wall decrease as the jejunoilium proceeds?
Decrease in thickness of both the inner circular and outer longitudinal muscular layers
Decrease in the number of plica circularis
- more plica = more absorption
What anchors the jejunoileum to the posterior body wall?
Mesentery proper/dorsal mesentery
What is the point of attachment for the dorsal mesentery?
The actual point of attachment or “root” begins at the point of re-peritonealizaton of the distal duodenum (part 4 located to the left of LV2) and extends across the posterior body wall in an inferior oblique direction to the level of the right sacroiliac joint, a course of six to seven inches.
One heck of a point.
What is housed in the dorsal mesentery?
Blood vessels
nerves
lymphatics, all to jejunileum
Fat storage, with increasing adipocytes as you approach the ileum
What is the approximate length of the large bowel?
~ 5 ft
What are the parts of the large bowel?
cecum + appendix ascending colon transverse colon descending colon sigmoid colon rectum anal canal
How is the large bowel different from the small bowel?
More distensible Thinner muscular layers haustra coli omental/epiploic appendages are enclosed within peritoneum Plica semilunares No villi removes water stores and compacts stool
How is the muscular layer different in the large bowel versus the small? What are the muscular parts?
It consists of three narrow bands (approx. 1 cm. in width), the teniae coli (libre, omentalis, meoscolica), which are spaced approximately equidistant from one another around the tube.
They begin at the appendix and extend to the rectum where they expand and fuse with one another to become a more robust and distinct layer.
What causes the haustra coli to form?
The teniae coli are shorter by 1/6 than the length of the colon. This causes the colon to be sacculated forming the haustra coli.
What is fusion fascia? What is unique about it?
The ascending and descending colon are secondarily retroperitoneal. The area dorsal to them represent areas of fusion between two planes of fascia: the formerly peritonealized colon and the peritoneum of the posterior body wall, forming fusion fascia.
It is unique because the ascending and descending colon can be safely approached surgically through these areas as no vessels or nerves traverse these planes of fascia.
What are the peritonealized portions of the large intestine?
appendix, cecum, transverse colon, sigmoid colon, superior rectum
What is the mesoappendix?
extension of dorsal mesentery to the appendix
Fixes appendix to posterior body wall
What is the transverse mesocolon?
suspends the transverse colon from the posterior body wall along a transverse line at approximately L1 L2
What is the sigmoid mesocolon?
suspends the sigmoid colon across the left pelvic brim to the third sacral segment
Where and what is the cecum?
Located in RLQ; peritonealized
Blind pouch at the proximal portion of the ascending colon
What is the ileocecal valve?
terminal ileum invaginates into the cecum to form the superior and inferior lips of the ileocecal valve
Is the iliocecal valve competent?
Although the circular muscle layer of the ileum is continued into the lips of the ileocecal valve, the valve is not competent. That is, contraction of the terminal ileum is more important in preventing reflux of cecal contents into the ileum.
Valve functions more like a sphincter
What and where is the appendix?
Blind-ending diverticulum; average length is 8 cm.
Occupies a retrocecal position (64%)
Is there any muscles associated with the appendix?
Possesses a complete coat of longitudinal muscle formed by the taenia coli which begin at the appendix
What is the location of the ascending colon?
Extends from the cecum to the right colic flexure
Retroperitoneal
What is the relationship between the ascending colon and the right paracolic gutter?
gutter is located between the ascending colon and the right lateral body wall
What is the location of the transverse colon?
Extends from the right colic flexure (hepatic) to the left colic flexure (splenic)
What are the attachments and ligaments associated with the transverse colon?
transverse mesocolon - hangs transverse colon from posterior body wall
gastrocolic ligament - attaches it to stomach
omental apron of greater ometum - anterior side
phrenicocolic ligament - attaches left colic flexure to left diaphragm
What is the course of the descending colon?
Extends from the left colic flexure to the pelvic brim
Descends on the posterior body wall musculature along the lateral border of the left kidney
Retroperitoneal
What is the relationship between the descending colon and the left paracolic gutter?
left paracolic gutter is located between the descending colon and the left lateral body wall
What is the course of the sigmoid colon?
Extends from the descending colon to the rectum
S shaped, beginning on the left side extending to the right and ending on the midline where it becomes continuous with the rectum
Why is the rectum divided into thirds?
due to partial peritonealization
What is the peritonealization of the proximal third of the rectum?
continuous with the sigmoid covered with peritoneum laterally and anteriorly
What is the peritonealization of the middle third of the rectum?
covered with peritoneum anteriorly only
What is the peritonealization of the distal third of the rectum?
rectal ampulla: dilated portion resting on pelvic diaphragm which exists below peritoneum. Peritoneum above the ampulla is reflected to the pelvic viscera or lateral and posterior pelvic wall.
What is the rectal ampulla?
dilated portion of distal rectum resting on pelvic diaphragm which exists below peritoneum
What is the musculature of the rectum?
Teniae coli fan out to form outer longitudinal muscle bands anterior and posterior to the rectum
Inner circular layer continuous with that of colon
What are the internal surface modifications of the rectum?
Transverse rectal folds
Ampulla
What are the transverse rectal folds? What do they functionally do?
typically three shelves composed of mucosa, submucosa and some circular muscle protrude from the walls of the rectum. They cause the external surface of the rectum to be thrown into curvatures or flexures; 2 on the left and one on the right. Functionally, they assist in supporting the fecal mass
What is the ampulla of the rectum?
dilated portion superior to pelvic diaphragm
What is the location of the anal canal?
From the front door of RVU to Michael Schwartz’s office.
Officially, it’s this:
Located in anal triangle between opposing ischioanal fossae; extends from pelvic diaphragm to anus
Located inferior to the ampulla of the rectum; angles 90o posteriorly due to the passage of the puborectal sling at point of junction of rectum and anal canal
What surrounds the anal canal?
Surrounded by ischioanal fat; allows for expansion during the elimination of feces
What is the internal anal sphincter continuous with? What is it’s innervation?
continuous with the inner circular muscle layer; therefore, it is involuntary in nature and autonomically innervated
What is the composition and innervation of the external anal sphincter?
circularly arranged skeletal muscle innervated by the inferior rectal branches of the pudendal n. (S 2,3,4)
What are anal columns?
vertical folds caused by veins deep to the mucous membrane
What are anal sinuses?
- depression between anal columns at anal valves
What are anal valves? What is the relationship between them and the pectinate line?
formed by venous anastomoses that connect the bases of contiguous anal columns and bridge across individual anal sinuses
The course of the anal valves creates a line known as the pectinate line.
What is Hilton’s White Line?
(intersphincteric line) - demarcates the point where the external sphincter meets the internal sphincter
What is the transitional area of the anus?
area between pectinate line above and Hilton’s white line below; demarcates area of epithelial change of the mucosa of the anal canal
Flip this card and look at the answers.
Review of changes occuring at the pectinate line: (listed above then below)
Epithelium: Columnar
Stratified squamous
Blood supply: Superior rectal artery
Inferior rectal artery
Venous drainage:
Portal
Systemic
Dilated veins:
Internal hemorrhoid External hemorrhoid
Sensory nerves:
Visceral
Somatic
Lymphatic drainage:
Internal iliac, Inf. mesenteric
Nodes
Superficial inguinal nodes
What is the origin of the superior mesenteric artery? Cord level?
Second unpaired ventral branch from the abdominal aorta
Arises in front of LV1 directly inferior to the origin of the celiac artery
What is the distribution of the SMA?
Entire small intestine (except for the proximal half of the duodenum), cecum, ascending colon and the proximal 2/3 of the transverse colon
What is the course of the SMA?
Arises behind the neck of the pancreas
Crosses the uncinate process and the third part of the duodenum to enter the mesentery of the small intestine
Follows a course parallel to the root of the mesentery inferiorward toward the cecum
Branches of the superior mesenteric artery will distribute to the intestines by traversing the mesentery which support them
What accompanies the SMA along its course?
superior mesenteric vein
Also the artery is invested with a thick network of nerve fibers, the superior mesenteric plexus, which conducts autonomic sympathetic and parasympathetic nerve fibers to all areas of the small and large bowel supplied by the superior mesenteric artery
What is the first branch of the SMA?
Inferior pancreaticoduodenal artery
What is the location of the inferior pancreaticoduodenal artery? What branches does it give off?
Arises at the pancreatic incisure (separates uncinate from neck)
Runs a short course (1 - 2 cm) to the right where it divides into: anterior and posterior inferior pancreaticoduodenal aa
What does the inferior pancreaticoduodenal artery anastamose with?
Anastomose with anterior and posterior superior pancreaticoduodenal aa., respectively forming anterior and posterior pancreatic arcades
What does the inferior pancreaticoduodenal artery anastamose supply?
Provide blood to the head of the pancreas and to Parts I, II, & III of the duodenum
What are the 5 branches of the SMA?
Inferior pancreaticoduodenal Intestinal aa (jejunal and ileal) Iliocolic Right colic Middle colic
What do the intestinal arteries from the SMA supply? What do they anastamose with?
Major blood supply to entire small bowel
Anastomose forming several generations of arterial arcades
Gives rise to vasa recta which penetrate the wall of the intestines
What structure do the intestinal arteries from the SMA course through?
Course in the mesentery proper
What is the terminal branch of the SMA? What does it head towards?
Iliocolic artery
Parallels the terminal intestinal artery
Courses toward the right iliac fossa to terminate at the ileocecal junction
What are the branches of the iliocolic artery?
Ascending branch colic branch anterior cecal artery posterior cecal artery appendicular artery ileal branch
What is the course of the right colic artery?
1) Inconstant branch from the right lateral side of the SMA; may arise as a branch from the ileocolic, middle colic or be entirely absent (13%)
What are the branches of the right colic artery? What are the anastomoses of each branch?
descending branch - ascending branch of colic artery
ascending branch - descending branch of the middle colic artery
Where is the middle colic artery? Where does it go?
2nd branch of the SMA
Arises from the front of the SMA
Ascends within the transverse mesocolon to gain the transverse colon
What does the middle colic artery split into? What does it anastomose with?
Usually bifurcates into right and left branches joined by an arcade which provide direct branches to the transverse colon
Right branch will anastomose with the ascending branch of the right colic a
Left branch will anastomose with the ascending branch of the left colic a.
What is the origin of the inferior mesenteric artery?
Third unpaired ventral branch from the abdominal aorta
Arises in front of LV3
What is the course of the inferior mesenteric artery? What does it supply?
Courses in a retroperitoneal position across the left posterior abdominal wall to descend into the pelvis
Distributes to the distal 1/3 of the transverse colon, descending colon, sigmoid colon and rectum
What nerves travel with the inferior mesenteric artery?
Its surface is invested by the inferior mesenteric plexus which conducts sympathetic nerve fibers to the distal transverse colon, descending and sigmoid colon
What are the branches of the inferior mesenteric artery?
left colic artery
sigmoidal arteries (2-3)
superior rectal artery
What is the location and course of the left colic artery?
Arises from the IMA in retroperitoneal position to course to the middle of the medial border of the descending colon
What does the left colic artery bifurcate into? Where does each branch go and what does it anastomose with?
Ascending branch - ascends the medial border of the descending colon to anastomose with the left transverse branch of the middle colic a
Descending branch - descends the medial border of the descending colon to anastomose with the ascending branch of the first sigmoid a
What is the course of the sigmoidal arteries?
Arise from the IMA in retroperitoneal position
Cross the posterior abdominal wall anterior to the left psoas major, ureter and gonadal vessels to enter the sigmoid mesocolon
What do the sigmoidal arteries supply?
Provide ascending & descending branches forming arcades from which vasa recta supply the sigmoid colon
What do the sigmoidal arteries anastomose with?
The ascending branch of the first sigmoid a. will anastomose with the descending branch of the left colic a.
The descending branch of the last sigmoid a. rarely will anastomose with the superior rectal a
What is the terminal branch of the IMA?
Superior rectal artery
What is the course of the superior rectal artery?
Crosses the left common iliac vessels
Courses within the sigmoid mesocolon to reach the rectosigmoid junction, where it bifurcates to form right and left branches which course on either side of the rectum
What arteries contribute to the marginal artery? What does the marginal artery protect against?
All colic branches of the SMA and IMA (ileocolic, right, middle and left, colic, and sigmoid aa.) anastomose along the mesenteric border of the entire colon forming the marginal artery (of Drummond).
This anastomosis helps to prevent necrosis of the bowel should one of the colic arteries become occluded.
What arteries supply the rectum and anal canal?
Superior rectal artery
Middle rectal artery
Inferior rectal artery
All three rectal aa. anastomose forming an intricate vascular supply to the rectum and anal canal
What is the parent artery of the superior rectal artery? What does it supply?
Branch of the inferior mesenteric a.
Supplies most of the muscular layer and mucosal lining of the rectum and upper portion of the anal canal
What is the parent artery of the middle rectal artery? What does it supply?
Branch of the internal iliac a.
Supplies the lower portion of the rectum, predominantly the muscular portion
What is the parent artery of the inferior rectal artery? What does it supply?
Branch of the internal pudendal a.
Provides major supply to the mucosa and muscular layer of the anal canal
What is the general definition for a portal system?
a vascular system that begins and ends in capillaries
Where does the hepatic portal system begin and end?
B. The hepatic portal system begins in the capillary beds of the digestive system and its accessory glands, including the gall bladder, pancreas and spleen, and ends in the capillary like venous sinusoids of the liver
What are the tributaries of the portal vein?
Inferior mesenteric vein with its rectal, sigmoidal and colic tributaries
Superior mesenteric vein with its intestinal, colic and pancreatic tributaries
Splenic vein with its gastric and pancreatic tributaries
Several veins drain directly to the portal vein, among them gastric, cystic and pancreaticoduodenal veins.
Where is the definitive portal vein? What is its course?
D. The definitive portal vein is formed dorsal to the neck of the pancreas at LV2 through the union of the superior mesenteric and splenic veins. The inferior mesenteric is most often a tributary of the splenic vein.
The portal vein courses posterior to the first part of the duodenum and enters the hepatoduodenal ligament posterior to the hepatic artery and common bile duct.
It then enters the liver at the porta and disperses its branches along the intrahepatic biliary duct network
Both hepatic arteries and portal veins then drain to the hepatic venous sinusoids.
