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GI > 1-7 Anatomy of the Infracolic Compartment > Flashcards

1-7 Anatomy of the Infracolic Compartment Flashcards

1
Q

What is the jejunoileum?

A

portion of the small intestine (jejunum and ileum) that connects the duodenum with the cecum of the colon

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2
Q

Why is the term jejunoileum used?

A

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.

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3
Q

When comparing the jejunum to the ilium, what are the differences?

A

the jejunum has:

  1. Greater diameter
  2. Thicker wall
  3. Increased number of circular folds
  4. Few lymphoid nodules
  5. Increased vascularity
  6. Deeper color
  7. Less mesenteric fat
  8. Arterial arcades are fewer
  9. Vasa recta are long
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4
Q

What is the location of the jejunum?

A

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.

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5
Q

What does the terminal ileum have to do with the iliocecal junction? What are the spatial relationships involved?

A

Note: The terminal ileum ascends from the pelvis to become continuous with the right colon at the cecum (ileocecal junction).

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6
Q

What is the approximate length of the jejunoilium?

A

~20 feet

Upper 2/5 (8 ft.) is jejunum; lower 3/5 (12 ft.) is ileum

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7
Q

Why does the thickness of the intestinal wall decrease as the jejunoilium proceeds?

A

Decrease in thickness of both the inner circular and outer longitudinal muscular layers

Decrease in the number of plica circularis
- more plica = more absorption

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8
Q

What anchors the jejunoileum to the posterior body wall?

A

Mesentery proper/dorsal mesentery

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9
Q

What is the point of attachment for the dorsal mesentery?

A

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.

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10
Q

What is housed in the dorsal mesentery?

A

Blood vessels
nerves
lymphatics, all to jejunileum

Fat storage, with increasing adipocytes as you approach the ileum

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11
Q

What is the approximate length of the large bowel?

A

~ 5 ft

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12
Q

What are the parts of the large bowel?

A 
cecum + appendix
ascending colon
transverse colon
descending colon
sigmoid colon
rectum
anal canal
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13
Q

How is the large bowel different from the small bowel?

A 
More distensible
Thinner muscular layers
haustra coli
omental/epiploic appendages are enclosed within peritoneum
Plica semilunares
No villi
removes water
stores and compacts stool
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14
Q

How is the muscular layer different in the large bowel versus the small? What are the muscular parts?

A

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.

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15
Q

What causes the haustra coli to form?

A

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.

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16
Q

What is fusion fascia? What is unique about it?

A

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.

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17
Q

What are the peritonealized portions of the large intestine?

A 
appendix, 
cecum, 
transverse colon, 
sigmoid colon,
superior rectum
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18
Q

What is the mesoappendix?

A

extension of dorsal mesentery to the appendix

Fixes appendix to posterior body wall

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19
Q

What is the transverse mesocolon?

A

suspends the transverse colon from the posterior body wall along a transverse line at approximately L1 L2

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20
Q

What is the sigmoid mesocolon?

A

suspends the sigmoid colon across the left pelvic brim to the third sacral segment

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21
Q

Where and what is the cecum?

A

Located in RLQ; peritonealized

Blind pouch at the proximal portion of the ascending colon

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22
Q

What is the ileocecal valve?

A

terminal ileum invaginates into the cecum to form the superior and inferior lips of the ileocecal valve

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23
Q

Is the iliocecal valve competent?

A

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

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24
Q

What and where is the appendix?

A

Blind-ending diverticulum; average length is 8 cm.

Occupies a retrocecal position (64%)

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25
Q

Is there any muscles associated with the appendix?

A

Possesses a complete coat of longitudinal muscle formed by the taenia coli which begin at the appendix

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26
Q

What is the location of the ascending colon?

A

Extends from the cecum to the right colic flexure

Retroperitoneal

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27
Q

What is the relationship between the ascending colon and the right paracolic gutter?

A

gutter is located between the ascending colon and the right lateral body wall

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28
Q

What is the location of the transverse colon?

A

Extends from the right colic flexure (hepatic) to the left colic flexure (splenic)

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29
Q

What are the attachments and ligaments associated with the transverse colon?

A

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

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30
Q

What is the course of the descending colon?

A

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

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31
Q

What is the relationship between the descending colon and the left paracolic gutter?

A

left paracolic gutter is located between the descending colon and the left lateral body wall

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32
Q

What is the course of the sigmoid colon?

A

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

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33
Q

Why is the rectum divided into thirds?

A

due to partial peritonealization

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34
Q

What is the peritonealization of the proximal third of the rectum?

A

continuous with the sigmoid covered with peritoneum laterally and anteriorly

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35
Q

What is the peritonealization of the middle third of the rectum?

A

covered with peritoneum anteriorly only

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36
Q

What is the peritonealization of the distal third of the rectum?

A

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.

37
Q

What is the rectal ampulla?

A

dilated portion of distal rectum resting on pelvic diaphragm which exists below peritoneum

38
Q

What is the musculature of the rectum?

A

Teniae coli fan out to form outer longitudinal muscle bands anterior and posterior to the rectum

Inner circular layer continuous with that of colon

39
Q

What are the internal surface modifications of the rectum?

A

Transverse rectal folds

Ampulla

40
Q

What are the transverse rectal folds? What do they functionally do?

A

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

41
Q

What is the ampulla of the rectum?

A

dilated portion superior to pelvic diaphragm

42
Q

What is the location of the anal canal?

A

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

43
Q

What surrounds the anal canal?

A

Surrounded by ischioanal fat; allows for expansion during the elimination of feces

44
Q

What is the internal anal sphincter continuous with? What is it’s innervation?

A

continuous with the inner circular muscle layer; therefore, it is involuntary in nature and autonomically innervated

45
Q

What is the composition and innervation of the external anal sphincter?

A

circularly arranged skeletal muscle innervated by the inferior rectal branches of the pudendal n. (S 2,3,4)

46
Q

What are anal columns?

A

vertical folds caused by veins deep to the mucous membrane

47
Q

What are anal sinuses?

A
  • depression between anal columns at anal valves
48
Q

What are anal valves? What is the relationship between them and the pectinate line?

A

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.

49
Q

What is Hilton’s White Line?

A

(intersphincteric line) - demarcates the point where the external sphincter meets the internal sphincter

50
Q

What is the transitional area of the anus?

A

area between pectinate line above and Hilton’s white line below; demarcates area of epithelial change of the mucosa of the anal canal

51
Q

Flip this card and look at the answers.

A

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

52
Q

What is the origin of the superior mesenteric artery? Cord level?

A

Second unpaired ventral branch from the abdominal aorta

Arises in front of LV1 directly inferior to the origin of the celiac artery

53
Q

What is the distribution of the SMA?

A

Entire small intestine (except for the proximal half of the duodenum), cecum, ascending colon and the proximal 2/3 of the transverse colon

54
Q

What is the course of the SMA?

A

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

55
Q

What accompanies the SMA along its course?

A

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

56
Q

What is the first branch of the SMA?

A

Inferior pancreaticoduodenal artery

57
Q

What is the location of the inferior pancreaticoduodenal artery? What branches does it give off?

A

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

58
Q

What does the inferior pancreaticoduodenal artery anastamose with?

A

Anastomose with anterior and posterior superior pancreaticoduodenal aa., respectively forming anterior and posterior pancreatic arcades

59
Q

What does the inferior pancreaticoduodenal artery anastamose supply?

A

Provide blood to the head of the pancreas and to Parts I, II, & III of the duodenum

60
Q

What are the 5 branches of the SMA?

A 
Inferior pancreaticoduodenal
Intestinal aa (jejunal and ileal)
Iliocolic
Right colic
Middle colic
61
Q

What do the intestinal arteries from the SMA supply? What do they anastamose with?

A

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

62
Q

What structure do the intestinal arteries from the SMA course through?

A

Course in the mesentery proper

63
Q

What is the terminal branch of the SMA? What does it head towards?

A

Iliocolic artery

Parallels the terminal intestinal artery

Courses toward the right iliac fossa to terminate at the ileocecal junction

64
Q

What are the branches of the iliocolic artery?

A 
Ascending branch
colic branch
anterior cecal artery
posterior cecal artery
appendicular artery
ileal branch
65
Q

What is the course of the right colic artery?

A

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%)

66
Q

What are the branches of the right colic artery? What are the anastomoses of each branch?

A

descending branch - ascending branch of colic artery

ascending branch - descending branch of the middle colic artery

67
Q

Where is the middle colic artery? Where does it go?

A

2nd branch of the SMA

Arises from the front of the SMA

Ascends within the transverse mesocolon to gain the transverse colon

68
Q

What does the middle colic artery split into? What does it anastomose with?

A

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.

69
Q

What is the origin of the inferior mesenteric artery?

A

Third unpaired ventral branch from the abdominal aorta

Arises in front of LV3

70
Q

What is the course of the inferior mesenteric artery? What does it supply?

A

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

71
Q

What nerves travel with the inferior mesenteric artery?

A

Its surface is invested by the inferior mesenteric plexus which conducts sympathetic nerve fibers to the distal transverse colon, descending and sigmoid colon

72
Q

What are the branches of the inferior mesenteric artery?

A

left colic artery
sigmoidal arteries (2-3)
superior rectal artery

73
Q

What is the location and course of the left colic artery?

A

Arises from the IMA in retroperitoneal position to course to the middle of the medial border of the descending colon

74
Q

What does the left colic artery bifurcate into? Where does each branch go and what does it anastomose with?

A

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

75
Q

What is the course of the sigmoidal arteries?

A

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

76
Q

What do the sigmoidal arteries supply?

A

Provide ascending & descending branches forming arcades from which vasa recta supply the sigmoid colon

77
Q

What do the sigmoidal arteries anastomose with?

A

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

78
Q

What is the terminal branch of the IMA?

A

Superior rectal artery

79
Q

What is the course of the superior rectal artery?

A

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

80
Q

What arteries contribute to the marginal artery? What does the marginal artery protect against?

A

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.

81
Q

What arteries supply the rectum and anal canal?

A

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

82
Q

What is the parent artery of the superior rectal artery? What does it supply?

A

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

83
Q

What is the parent artery of the middle rectal artery? What does it supply?

A

Branch of the internal iliac a.

Supplies the lower portion of the rectum, predominantly the muscular portion

84
Q

What is the parent artery of the inferior rectal artery? What does it supply?

A

Branch of the internal pudendal a.

Provides major supply to the mucosa and muscular layer of the anal canal

85
Q

What is the general definition for a portal system?

A

a vascular system that begins and ends in capillaries

86
Q

Where does the hepatic portal system begin and end?

A

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

87
Q

What are the tributaries of the portal vein?

A

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.

88
Q

Where is the definitive portal vein? What is its course?

A

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.

GI (26 decks)

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