Colon & Rectum Flashcards
Foregut structures extend all the way to?
2nd part of duodenum
rely on celiac artery
Midgut structures of abdomen?
extends from duodenal ampulla to distal tranverse colon (rely on SMA)
Hindgut structures?
distal third of t-colon, descending colon, rectum
rely on IMA
Avg. diameter and length of cecum?
diameter is 7.5 cm
length approx. 10 cm
Acute dilatation of cecum greater than what number can result in acute ischemic necrosis and bowel perforation?
> 12 cm
Most common location of appendix in relation to the cecum?
retrocecal 65% of time
pelvic 30% of time
These two parts of the colon are retroperitoneal in nature:
ascending + descending colon
How do we mobilize the colon and its mesentery from the retroperitoneum?
dissect along the white line of Toldt
What is the white line of Toldt?
represents the fusion of the mesentery with the posterior peritoneum
What ligaments tether the colon to the hepatic flexure and the splenic flexures?
hepatic flexure; nephrocolic ligament
splenic flexure; phrenocolic ligament
How do we get to the splenic flexure when mobilizing the colon?
dissecting the descending colon upward via white line of Toldt
then lesser sac is entered by reflecting the omentum away from t-colon
Attached to anterior surface of t-colon is greater omentum, which has how many layers?
fused double layer of parietal and visceral peritoneum (4 layers)
contains stored fat
The descending colon, lies ventral to left kidney and extends downward for how long?
25 cm
Where do we see a transition from the thin walled, fixed, descending colon to the mobile sigmoid colon?
level of pelvic brim
In relation to the sigmoid colon, it has a long floppy mesentery, often attached to left pelvic sidewall, producing a small recess called the intersigmoid fossa, often a landmark for what?
left ureter
Rectum along with sigmoid serve as what?
fecal reservoir
The rectum is usually 12-15 cm in length usually lacks what?
tenia coli and appeploic appendages
Why do we say the rectum posterior surface is almost completely extraperitoneal?
its adherent to presacral soft tissues, thus outside the peritoneal cavity
Anterior surface of proximal third of rectum covered by visceral peritoneum, what is this anterior space called?
Pouch of Douglas
What’s the pouch of douglas?
recto-uterine pouch
can serve as site of drop mets from visceral tumors
What’s Bloomer’s shelf?
drop mets from visceral tumors can fall into the pouch of Douglas and form a mass there
often detected by digital rectal exam
Rectum possesses three curves or involutions, known as?
valves of Houston
have no function, don’t impede flow
usually lost after surgical mobilization of rectum
Mobilization of rectum leads to loss of the 3 rectal curves called the valves of Houston, thus adding how much extra rectal tissue?
approx. 5 cm
great for anastomosing in the pelvis
The rectum is intimately close to the presacral fascia, but it is not directly adhered to it, what separates it?
posterior aspect of rectum covered by mesorectum and the mesorectum covered by a thin layer of investing fascia called fascia propria
fascia propria prevents direct rectal adherence to presacral fascia
serves as a bloodless plane for oncologic rectal surgery
What is Waldayer’s fascia?
recto-sacral fascia
thick fascia connecting the presacral fascia to the fascia propria of rectum at the level of S4
Why is Waldayer’s fascia an important surgical landmark?
its division during dissection from abdominal approach leads to entry into deep retrorectal pelvis
What 3 muscles collectively termed the levator ani form the pelvic floor?
pubococcygeus
iliococcygeus
puborectalis
What muscle permits descent of feces?
relaxation of puborectalis straightens the anorectal angle and allows fecal descent
contraction causes the opposite
Puborectalis is in a constant state of contraction or relaxation?
Contraction–> important for continence
Arterial supply to the foregut, midut and hindgut?
Celiac A–> foregut
SMA–> midgut
IMA–> hindgut
Anastomosis of SMA and IMA?
SMA ends at distal t-colon
IMA begins at splenic flexure
Marginal artery of Drummond forms a communication arcade between these two vessels along the mesentery of colon
SMA supplies what??
entire small bowel via 12-20 jejunal-ileal branches to the left
3 main colonic branches to the right (right colic, middle colic, ileo-colic)
Ileo-colic artery supplies?
terminal ileum
cecum
appendix (via appendicular branch)
The middle colic artery off of the SMA supplies what?
gives of left and right branch
supplies proximal and distal T-colon
Griffith’s point?
watershed area by splenic flexure, where left branch of middle colic off of SMA and left colic artery from IMA don’t have a strong communication
anastomosis usually avoided by splenic flexure due to tenuous blood supply
Where do we find the IMA anatomically?
level of L2-L3
3 cm above aortic bifurcation into iliacs
Branches off of IMA?
left colic artery
sigmoid branches
superior rectal artery
What is the arc of Riolan?
AKA meandering mesenteric artery
connects proximal SMA to proximal IMA
Meandering mesenteric artery, AKA arc of Riolan is what?
connects proximal SMA to proximal IMA
Blood supply of rectum?
superior rectal artery –> IMA
middle rectal artery–> internal iliac A
inferior rectal artery–> pudental artery–> internal iliac A
Venous drainage of right and proximal tranverse colon?
SMV (joins splenic vein to go into portal vein)
Distal t-colon, descending colon, sigmoid colon, and most of rectum drain via what vein?
IMVA (joins splenic vein)
Anal canal venous drainage?
drained by middle + inferior rectal veins
empty into the internal iliac vein–> IVC
50% of fecal mass is comprised of?
bacteria
Most colonic bacteria are?
anaerobic species
Principle source of nutrition for colonocytes?
short chain fatty acids–> created by bacterial breakdown of starches
What species of bacteria predominate throughout the colon?
bacteroides species
e.coli, klebsiella, proteus, lactobacillus make up the rest
Unlike most of the mucosal lining of the proximal GI tract, colonic mucosa do not receive nutrition primarily from blood stream but from?
primary energy source if short chain fatty acid butyrate
Primary energy source for colonic epithelium?
butyrate (SCFA)
Na and H2O absorption in colon, active or passive?
H2O–> passive
Na–> active
Mammal cells do not produce butyrate, how do colonic cells get it?
bacteria ferment ingested dietary fiber
Broad spectrum antibiotics destroy local colonic bacteria, thus fermentation of dietary fiber does not occur, thus we don’t have energy for colonocytes to absord Na and water thus we get?
watery diarrhea
How do we define diarrhea?
> 3 loose stools daily
How do we define constipation?
< 3 stools weekly
Most common bacterial species in the colon?
most common bacteria-> bacteroides (anaerobic)
aerobic–> e.coli
Bowel prep and pre-op antibiotics before colonic surgical manipulation?
commonly done in US
(however, some think broad spectrum antibiotics can destroy the normal colonic bacteria, reduce butyrate, less energy for colonocytes, weaker anastomosis)
Absolute contraindications to bowel prep?
complete bowel obstruction
free perforation
Elective colo-rectal cases are classified as?
clean-contaminated
When an elective clean contaminated colo-rectal case is done we need post-op abx?
routine abx for a clean contaminated segmental resection does not reduce infectious complications
promotes c. diff colitis
Typical abx used pre-operatively for elective colonic cases?
2, 3rd gen cephalosporins or fluroquinolone + flagyl or clinda
What is diverticular disease of colon?
abnormal sac or pouch protruding from colonic wall
colonic diverticula are pseudodiverticula (protrusions of mucosa thru the muscularis layers)
Why are colonic divericula pseudodiverticula and not true?
true diverticulum–> all layers of colon protrude thru
pseudo–> they don’t protrusion of normal muscular layers
Age distribution of diverticula?
rare before age 30
2/3 of Americans will have diverticula by age 80
Dietary factors contributing to diverticulosis?
low fiber diet
diet high in carbs and meats
What causes diverticula to form in the colon?
herniations of mucosa thru the colon at sites of penetration of the muscular wall by arterioles
Why do we commonly see bleeding with diverticulosis?
usually diverticula are protrusion of mucosa thru the colonic wall at sites where the arterioles penetrate the muscular wall
sometimes the arterioles are involved in the protrusion and form the dome of the diverticula
Why are colonic diverticula called false diverticula?
they only contain protrusions of mucosa
Where do diverticula form on the colon?
they form on the mesenteric sides
Do not form on the anti-mesenteric sides
Diverticula affect what part of colon mostly?
sigmoid colon 50%
descending colon 40%
Why is sigmoid common site for diverticula?
has smallest colonic diameter
decrease in fiber, requires increased pressures to propel feces forward
narrow sigmoid can generate pressures as high as 90 mmHg to propel feces forward–> diverticula
What causes diverticulitis?
perforation of a colonic diverticula
This is an extraluminal pericolic infection caused by extravasation of feces thru a perforated diverticulum:
diverticulitis
Symptoms of diverticulitis?
LLQ pain alterations in bowel habits fever/chills urinary urgency no rectal bleeding
Preferred imaging modality to reveal diverticulitis?
CT
What is the Hinchey classification of diverticulitis?
I–> pericolic or mesenteric abscess
II–> walled-off pelvic abscess
III–> generalized purulent peritonitis
IV–> generalized fecal peritonitis