Colon

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anders
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248016
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Colon
Updated:
2013-11-21 00:50:16
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Colon
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  1. Describe the layers of the colon:
  2. What are plicae semilunares?
    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)
  3. Describe the peritoneal/retroperitoneal sections of the colon.
    • Retroperitoneal - ascending & descending colon
    • Peritoneal - transverse & sigmoid
  4. Describe the relationship of the rectum and peritoneum
    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

  5. What is the daily absorptive capacity of the colon?
    • 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
  6. Describe electrolyte exchange by the colon
    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)

  7. Main anions in the stool:
    short-chain fatty acids: butyrate, acetate, propionate

    produced by bacterial breakdown of nonstarch polysaccharides or dietary fiber such as lignin, cellulose, & fruit pectins
  8. Main fuel for colonic epithelial cells =
    Butyrate

    (A bacterial fermentation product)
  9. Factors that influence colonic transit time:
    • Fermentability of nonstarch polysaccharides
    • stool pH
    • autonomic nervous system
    • gastrocolic reflex (postprandial increase in electrical activity and colonic tone)
  10. What antibiotics are NOT associated with Pseudomembranous enterocolitis?
    • Vancomycin
    • antimicrobials used to treat mycobacteria, fungi, or parasites
  11. Time course of diarrhea onset in Pseudomembranous enterocolitis
    During or up to 3 weeks after cessation of antibiotic therapy
  12. Pseudomembranous enterocolitis diagnosis:
    • colonoscopy - raised mucosal plaques
    • cytotoxic assay for Cdiff exotoxin
  13. Pseudomembranous enterocolitis treatment:
    • 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
  14. Indications for surgery for Pseudomembranous colitis
    • 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%
  15. Amebic colitis causative organism:
    Entamoeba histolytica

    Transmitted through food/water contaminated with feces containing Entamoeba cysts
  16. Percentage of the American population that are asymptomatic carriers:
    10%
  17. Acute vs. Chronic amebic dysentery manifestations:
    Acute - fever, cramps, bloody diarrhea

    Chronic - 3-4 foul-smelling bowel movements per day, abdominal cramping, fever
  18. Amebic colitis diagnosis:
    • 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)
  19. Amebic colitis treatment:
    • 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
  20. Actinomycosis causative organism:
    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)
  21. Abdominal actinomycosis treatment:
    • surgical drainage
    • PCN or tetracycline
  22. Lymphogranuloma venereum causative organism:
    Chlamydia trachomatis

    Transmitted sexually, usually by men-men
  23. Lymphogranuloma venereum clinical manifestations:
    • Proctitis
    • tenesmus
    • discharge
    • bleeding
    • perianal/rectovaginal fistulas
    • rectal strictures

  24. Lymphogranuloma venereum diagnosis & treatment:
    • 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.
  25. Tuberculous enteritis clinical manifestations & treatment:
    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
  26. Mesenteric adenitis causative organism, clinical features & treatment:
    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
  27. Most common symptoms of ischemic colitis:
    • 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
  28. Most common location of ischemic colitis:
    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

  29. What is the Sudeck's point?
    • 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.
  30. What is Griffith's point?
    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.

  31. Ischemic colitis diagnosis:
    • colonoscopy - cyanotic, edematous mucosa that may be covered with exudative membranes
    • barium enema - "thumb-printing" of the bowel wall
  32. Ischemic colitis treatment:
    • Transient - nonoperative
    • Gangrenous (s/s peritonitis) - resection with end colostomy
    • Ischemic strictures - elective resection and primary anastamosis
  33. Blood supply of the colon & rectum:
    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

              
  34. Total blood flow to GI tract:

    Distribution across GI tract layers, sm vs lg bowel:

    During a meal:

    During exercise:
    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%
  35. Most common aerobic and anaerobic organisms in the colon:
    aerobic - Escherichia coli

    anaerobic - Bacteroides
  36. Bowel prep recommendations"
    • Administer broad spectrum IV antibiotic within 30min of skin incision
    • (Ancef, Cefotetan)

    Mechanical bowel prep of questionable utility.
  37. Causes of anastamotic leaks:
    • 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)

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