93. Colon

Question 1

branches of caudal mesenteric artery

Answer 1

1. left colic (feeds descending colon)2. cranial rectal

Question 2

where does the transverse colon lie in relation to the root of the mesentery

Answer 2

cranial to cranial mesenteric artery and the root of the mesentery

Question 3

at what point does the descending colon become the rectum

Answer 3

anatomically indistinguishablenear pelvic inlet2 cm CRANIAL to pelvic brim but 1 cm CAUDAL from caudal mesenteric artery

Question 4

branches of the cranial mesenteric artery

Answer 4

1. jejunal, ileal 2. common colic artery (ileocolic–cecal and antimesenteric, right and middle colic)

Question 5

what is the vasa recti

Answer 5

arteries connect to the colon via vasa recti (short irregular branches that bifurcate upon entering the intestine

Question 6

2 arterial networks of the colon

Answer 6

1. subserous2. mural (direct and plexiform anastomoses that lie predominately in the submucosa)

Question 7

cells present in the epithelial mucosa layer of the colon

Answer 7

columnar epitheliumcuboidal epitheliumnumerous goblet cellsenterochromaffin cells (5%)NO VILLINO aggregated lymph folliclesinstead have relatively large lymphoglandular complexes

Question 8

autonomic plexuses of the abdominal region

Answer 8

1. cranial mesenteric plexus–main artery common colic –supplies large intestine–cranial mesenteric ganglion2. caudal mesenteric plexus–left colic artery: lumbar splanchnic nerves supplies paired hypogastric nerves–cranial hemorrhoidal artery: aortic plexus supplied distal colon

Question 9

key functions of the colon

Answer 9

1. storing fecal material2. reservoir for complex essential microbial ecosystem3. maintain fluid/electrolyte balance through resorting water/Na/Cl/fatty acids (secretes K/HCO3/mucus)

Question 10

area of colon with most absorptive capacity

Answer 10

proximal (segmental/mixing motility)(distally the colon is primarily involved with fecal storage but still modulates fecal water content)in general, absorbs 1.5L/day of fluid

Question 11

T/Fcolonocytes are able to switch from absorption to secretion when stimulated by hormones/secretagogues

Answer 11

TRUE–aldosterone (favors absorption)–other hormones may favor secretiondisruption of this balance of ion transport leads to disease (constipation or diarrhea); under control of complex endocrine, autocrine, paracrine and neuronal stimuli

Question 12

T/Fmost Na absorption in colon is electroneutral path

Answer 12

TRUEthrough Na/H exchangers (three types)ENHANCED Na absorption is through an electrogenic route (maintains electrochemical gradient—Na/Cl co transport)

Question 13

net movement of water occurs through which process

Answer 13

osmotically driven active absorption and secretionoccurs via paracellular and transepithelial routes (aquaporin-4)

Question 14

what ion pump is responsible for maintaining homeostasis essential to secretion of mucus

Answer 14

Na/2Cl/K co transporter type 1 protein in the basolateral membrane

Question 15

where do short chain fatty acids come from in the colon?

Answer 15

products of colonic bacterial fermentation of dietary fiber (butyrate, acetate, propionate)absorbed with Na/Clhave a marked trophic effect on colonic epithelium and stimulate Na absorption through acidification and activation of apical Na/H transportalso stimulate HCO3 release/secretion and thus absorption of Clalso prevent colonic irritation

Question 16

motility in colon

Answer 16

segmental–mixing: proximal and midcolonpropulsive aboral peristalsis –distal colonunder intrinsic plexus control:–myenteric (Auerbach): btwn long and circular muscle layers–submucous (Meissner): in colonic submucosaPSNS: preganglion vagus, pelvic n STIMULATESYM: superior and inferior mesenteric plexus, hypogastric n INHIBIT

Question 17

innate local defense of colon

Answer 17

–impermeable barrier–rapidly renewing–constantly moving–mucus–cryptdins (alpha defensins)–lysozyme–phospholipase–chemokinesPREVENTS COLONIZATION/INVASION of bacT

Question 18

adaptive immunity of the colon

Answer 18

part of a more specific, long term response for memory and rapid elimination of any pathogen1. antigen presenting cells: M (microfold) cells: no villi or enzymes, just proinflm cytokines and invaginate to present pathogen to T and B cellsD (dendritic) cells: interact with M, B, T cells; can also penetrate lumen to sample antigens2. intraepithelial lymphocyte:express CD8 alpha alpha (like mucosal T cells)

Question 19

3 phases of GI wound healing

Answer 19

1. lag (inflammation/debridement)–some separate these stages: 0-4 days post op includes fibrin clot, PMN, then macros, minimal wound strength and collagenase activity is high2. proliferation: 4-14d; fibroblasts prolif and make collagen III > I; under cytosine influence (FGF, TGF beta, PDGF); angiogenesis3. maturation (and remodel): day 17 onward; less type III collagen. All types I, III, IV is present in GI wound healing

Question 20

most critical stage of healing in which dehiscence or breakdown of repair is most likely to occur

Answer 20

LAG phase (inflammation and debridement phase)3-4 days post op72-96 hours

Question 21

collagen content of GI submucosa

Answer 21

I 70%III 20%IV 10%made by fibroblast and smooth muscle cells

Question 22

when does the colon have 75% of its strength return

Answer 22

4 months30% strength after 48hr

Question 23

factors negatively affecting wound healing of the colon

Answer 23

LOCAL–wound shear stress/tension (intraluminal transport and peristalsis)–down regulated vascular perfusion in shock–poor wound apposition–infection (anaerobic/aerobic bacterial flora present)SYSTEMIC–hypovolemic–nutrient deficiency (Zn, Iron needed for protein synthesis)–chemotx–immunocompromised state

Question 24

at what PaO2 will collagen NOT occur

Answer 24

below 40 mm Hg collagen formation will not occur below 10 mm Hg angiogenesis and epithelial hyperplasia will fail

Question 25

methods for improving colonic wound healing

Answer 25

–correct hypovolemia–minimal tension–preserve local blood supply–use vacularized tissue wraps (omentoplasty +/- vascular rectus abdominis muscle flap)–colonic reinforcement with biomaterial (SIS)–experimental VEGF administration to promote angiogenesis

Question 26

T/Fappositional pattern of colonic closure leads to less scar than inverting or everting suture patterns

Answer 26

trueappositional has less scar and less reduction in luminal diameter(though simple continuous may decrease surgical time and achieve better histological alignment of layers with minimal tissue handling–has also been reported)

Question 27

closure options for colon sx

Answer 27

1. hand sewn—simple interrupted (preferred) or simple continuous SINGLE layer appositional2. GIA with TA–eversion3. EEA (transcecal, through enterotomy, transrectal) –inversion4. skin staples (small intestinal described, not clinically described for large intestine)5. biofragmentable anatosmotic ring (polyglycolic acid and barium)—performed in cats with subtotal colectomy (limited sizes available—may have serosal tearing)6. sutureless closure (laser, cyanoacrylates, fibrin glue)–NOT clinically experimented

Question 28

colonogram contrast agent and recommendations

Answer 28

1. soapy enema 2-4 hours prior2. barium diluted 50:50 warm water give 10 ml/kg trans rectally (use balloon catheter to prevent leak)can also use double contrast (provide air after evacuating barium)

Question 29

prep for endoscopy/colonoscopy

Answer 29

1. fast 24-48 hr2. oral cleansing solution (may need orogastric tube) 20–30 ml/kg +/- repeat dose 2 hrs later3. two warm water enemas 20 ml/kg morning of scope and one hour before procedure4. left lateral recumbency so transverse colon drains out

Question 30

choice of perioperative antibiotics based on contaminants present

Answer 30

coliforms and anaerobes–higher generation cephalosporin(Cefoxitin)–combo first gen ceph with anaerobic Ab (cefazolin, metronidazole)

Question 31

Define parker kerr suture pattern

Answer 31

—continuous cushing over a Doyen clamp, tightened when the clamp is removed–followed by inverted continuous lembert pattern (oversewn)

Question 32

indications for colonic R&A

Answer 32

–neoplasia–megacolon–perforation–trauma–chronic intussusception (irreducible/necrotic)–colonic torsion

Question 33

difference btwn subtotal vs total colectom

Answer 33

subtotal–preserve ileocolic junction (cut 1-2 cm aboral to ileocolic jxn)total–resect including ileocolic jxn (cut 1-2 oral to ileocecal fold)importance of ileocolic junction is debated: though to prevent colonic reflux into SI; removal may lead to colonic bacT in SI and lead to SIBO–>diarrhea

Question 34

T/Fsingle surgical field approach should be used in cats when using a EEA stapler

Answer 34

TRUEno long term complications in 15 cats with single field approach vs 2/10 complications with dual field approach and transrectal application of EEA

Question 35

two types of colostomy

Answer 35

1. end on colostomy (flank exteriorized)2. loop colostomyall render patient fecally incontinent

Question 36

what term has been given to acquired megacolon that developed from mechanical obstruction (pelvic stenosis, neoplasm, FB, etc)

Answer 36

hypertrophic megacolonpotentially reversible if cause of obstruction is removed early in disease process (within 6 months of initial trauma)(most common cause pelvic fracture malunion)

Question 37

causes of megacolon in dogs and cats

Answer 37

congenital===RAREacquired–extraluminal compression (prostatomegaly, pelvic deformity/chronic factures, pelvis masses, strictures–post neuter/OHE)–intraluminal obstruction (FB, neoplasia, stricture)–metabolic (hypoK, hypoT)–NM dysfunction (sacral spinal cord deformitis–Manx, ileus, dysautonomia, idiopathic)–failure to fix perineal hernia

Question 38

feline idiopathic megacolon

Answer 38

62%middle aged male catsgeneralized dysfunction of long and circular muscle layer no evidence of physical or functional obstruction

Question 39

megacolon diagnosis on lateral radiograph

Answer 39

normal colon is length of body of L2megacolon = colonic diameter >1.5x length of the body of L7

Question 40

MOA of lactulose therapy for treatment of megacolon

Answer 40

osmotic laxativedisaccharideNOT hydrolysable to mammal Stays in colon for bacT fermentation into organic acids/osmostic/pulls water into stool

Question 41

MOA of cisapride therapy for treatment of megacolon

Answer 41

benzamine prokineticcauses release of Ach from enteric neurons to stimulate contraction in descending colonworks better in cats with mild/moderate dzeffects may only be transientwithdrawn from market due to cardiotoxicity in people

Question 42

how long does it take normal enteric plexuses to reestablish

Answer 42

8 weeks for normal enteric plexuses and motility to reestablish

Question 43

diarrhea following total or subtotal colectomy

Answer 43

loose stools are expected bc of loss of absorptive capacity and decreased transit timepost op motility reestablished ~8 weeksremaining intestine adapts by increasing villus height and enterocyte number and density (may take months)

Question 44

complications following colon surgery

Answer 44

–diarrhea with massive resection (may adapt over months and small proportion may have loose stools for years)–stricture at surgical site rare but reported within 3 weeks–recurrence of constipation (45% based on 22 cats)–recurrence of neoplasia–dehiscence/leakage/peritonitis

Question 45

colonic/cecocolic volvulus

Answer 45

–young to middle aged medium to large breed dogs–prognosis depends on severity and prompt survival intervention

Question 46

causes of reported colonic entrapment

Answer 46

–post OHE/neuter: resect fibrous band–good px–herniation through duodenocolic ligament–good px without intestinal strangulation

Question 47

colonic neoplasia

Answer 47

majority malignantdogs: adenocarcinoma, GIST, leiomyocarcomacats: LSA, adenocarcinoma5-8 cm resection recommended (recurrence likely with incomplete margins)palliative use of colonic stents reported

Question 48

MST in dogs with intestinal GIST vs leiomyosarcoma

Answer 48

MST GIST 37 monthsMST leiomyocarcom 8 months

Question 49

classification of colonic duplication

Answer 49

1. rectal, colon2. rectal, colon with other congenital abN (urogenital duplication, vertebral abN)1. spherical noncommunicating2. tubular noncommunicating3. tubular communicating