Colon

spaced, transverse, crescentic folds that separate the tissue between the taeniae coli and form haustra

• They produce a characteristic, intermittently bulging pattern that is radiographically distinct from small intestine
• (small intestine has plicae circulares/valvulae conniventes)

• Retroperitoneal - ascending & descending colon
• Peritoneal - transverse & sigmoid

Proximal rectum - completely covered by peritoneum except for a thin dorsal strip where mesorectum suspends rectum to pre-sacral tissue

Middle rectum - covered by peritoneum ventrally

Distal rectum - not covered by peritoneum

• water: 1-2L/day (can increase to 5-6L/day)
• Na: 200mEq
• Cl: 200mEq

Cecum and right colon absorb the most rapidly; the rectum is impermeable to Na & water

Na+ is actively absorbed against chemical and electrical gradient

K+ & Cl- are secreted through the sodium-potassium ATPase and the sodium-potassium-chloride cotransporters.

Cl- is actively absorbed in exchange for HCO3- (absence of luminal Cl- inhibits bicarb secretion)

short-chain fatty acids: butyrate, acetate, propionate

produced by bacterial breakdown of nonstarch polysaccharides or dietary fiber such as lignin, cellulose, & fruit pectins

Butyrate

(A bacterial fermentation product)

• Fermentability of nonstarch polysaccharides
• stool pH
• autonomic nervous system
• gastrocolic reflex (postprandial increase in electrical activity and colonic tone)

• Vancomycin
• antimicrobials used to treat mycobacteria, fungi, or parasites

During or up to 3 weeks after cessation of antibiotic therapy

• colonoscopy - raised mucosal plaques
• cytotoxic assay for Cdiff exotoxin

• Vancomycin 125mg PO QID x10 days
• Metronidazole 250-500mg PO/IV QID x7-14 days

(Oral Vancomycin safe for use in pregos)

Relapse rate: Vanco - 20%, Metro - 23%

Surgical treatment = subtotal colectomy

• signs of peritoneal inflammation
• severe ileus
• toxic megacolon

Pts who benefit most are >65yo, immunocompetent, have severe leukocytosis, have lactic acidosis

30-day mortality = 53%

Entamoeba histolytica

Transmitted through food/water contaminated with feces containing Entamoeba cysts

10%

Acute - fever, cramps, bloody diarrhea

Chronic - 3-4 foul-smelling bowel movements per day, abdominal cramping, fever

• warm saline prep of stool demonstrating trophozoites containing ingested erythrocytes
• serologic test for E. histolytica antibodies (+ in 90% of pts with active amebiasis)
• sigmoidoscopy - extensive ulceration of the intestinal epithelium (active, can be normal in 30% of chronic cases)

• Acute:
• Metronidazole 750mg PO TID x10 days

• Chronic:
• Diiodohydroxyquin 650mg TID x20 days +
• Metronidazole 500mg PO TID x10 days OR
• Diloxanide furoate 500mg TID x10 days

Actinomyces israelii - anaerobic, gram+

Part of normal oral flora

Can produce chronic inflammatory induration & sinus formation in the cervicofacial area, thorax, or abdomen (cecum most common abdominal site)

• surgical drainage
• PCN or tetracycline

Chlamydia trachomatis - 

Transmitted sexually, usually by men-men

• Proctitis
• tenesmus
• discharge
• bleeding
• perianal/rectovaginal fistulas
• rectal strictures

• Frei intracutaneous test (historical)
• complement fixation test

Tx: Tetracycline, +/- steroids

Currently, the Frei intradermal test is only of historical interest. The test was based on a positive hypersensitivity to an intradermal standardized antigen, lymphogranuloma venereum, which indicated past or present chlamydial infection. The Frei test would become positive 2-8 weeks after infection. Unfortunately, the Frei antigen is common to all chlamydial species and is not specific to LGV. Commercial manufacturing of Frei antigen was discontinued in 1974.

Complement fixation (CF) is more sensitive than the Frei skin test, but it has some cross-reactivity with other chlamydial species. CF sensitivity is 80% for LGV. A test titer of 1:16 is strongly suggestive of LGV and a titer of >1:64 indicates active LGV. A 4-fold rise or fall in titer further supports the diagnosis.

The microimmunofluorescence test for the L-type serovar of C trachomatis is a more sensitive and specific test. A titer greater or equal to 1:512 is diagnostic. Availability of this test is the limiting factor.

Polymerase chain reaction (PCR) assays have been used for diagnosis recently in several outbreaks. PCR is a far superior test but has limited availability to reference laboratories. Recently, multiplexed real-time PCR assays have been developed for the rapid detection of Chlamydia trachomatis and specific serovars.

Definitive diagnosis may be made by aspiration of the bubo and growth of the aspirated material in cell culture. C trachomatis can be cultured in as many as 30% of cases.

most commonly seen in the ileocecal region

• stenosis of the distal ileum, cecum, & ascending colon
• may appear similar to Crohn's disease

• Triple-drug therapy: Isoniazid, p-aminosalicylic acid, streptomycin
• Surgery if obstruction

Yersinia enterocolitica - anaerobic, gram neg rod

transmitted through food contaminated by feces/urine (puppies!, daycare centers)

• primarily affects ileocecal region
• Can mimic appendicitis, Crohn's

Tx: tetracycline, streptomycin, ampicillin, kanamycin

• lower abdominal pain
• bright red rectal bleeding

especially in elderly patient or any pt with hypercoagulable state, periarteritis nodosa, SLE, RA, polycythemia vera, and scleroderma

Splenic flexure or distal sigmoid colon

Ischemic colitis is a disease of small arterioles and the suboptimal blood flow in these areas between two vascular systems (watershed areas) makes them vulnerable

• The area between the blood supply from the last sigmoid artery and the superior rectal artery.
• 

Clinical significance is questionable since there is retrograde flow from the middle and inferior rectal arteries.

The are at the splenic flexure that is positioned between areas perfused by the left branch of the middle colic artery and the ascending branch of the left colic artery.

• colonoscopy - cyanotic, edematous mucosa that may be covered with exudative membranes
• barium enema - "thumb-printing" of the bowel wall

• Transient - nonoperative
• Gangrenous (s/s peritonitis) - resection with end colostomy
• Ischemic strictures - elective resection and primary anastamosis

Right & transverse colon - derived from foregut; blood supply from Superior Mesenteric Artery --> ileocolic, right colic, middle colic branches

• Left & sigmoid colon - derived from hindgut; blood supply from the Inferior Mesenteric Artery --> left colic, sigmoid branches
•           

Rectum - derived from hindgut; blood supply from IMA --> superior hemorrhoidal artery + Internal Iliac Artery -->middle hemorrhoidal artery + Internal Pudendal Artery --> inferior hemorrhoidal arteries

          

25mL/kg/min; 20% of cardiac output

• 80% - mucosa & submucosa
• 20% - muscularis
• large bowel receives 50% of what the small intestine receives (therefore is more sensitive to ischemic injury)

blood flow increases to 50% above normal (no corresponding increase in CO)

blood flow decreases by 20%

aerobic - Escherichia coli

anaerobic - Bacteroides

• Administer broad spectrum IV antibiotic within 30min of skin incision
• (Ancef, Cefotetan)

Mechanical bowel prep of questionable utility.

• Definitive:
• - poor blood supply
• - tension on the suture line

• Implicated:
• - use of drains
• - advanced malignancy
• - shock
• - malnutrition
• - environment: radiation therapy, emergency operations, contaminated fields, Crohn's
• - smoking
• - steroid use
• - male gener (narrow pelvis)
• - technical reasons (increased risk in anastamoses below peritoneal reflection & length of rectal stump d/t increased difficulty)