Disease of the Large Intestine Flashcards
What’s the definitive of the proximal and distal colon?
proximal colon = ascending and transverse colon
distal colon = descending colon
Which hormone stimulates epithelial growth in the large intestine?
Growth hormone
What’s a major difference in the mucosal layer between the small and large intestines?
Large intestine doesn’t have villi - it’s smooth mucosa with a large number of goblet cells
What are the functions of the goblet cells in the large intestines?
To produce mucus (lubrication, passage of feces, and inhibits bacterial invasion)
Which type of lymphocyte is predominately found in the large instestine?
CD8+ T cells
What’s the predominately type of lymphocytes found in the large intestine lamina propria?
CD4+ T cells, IgA secreting B cells, and plasma cells
Where are the interstitial cells of Cajal located in the large intestine? What’s their function?
- It’s located on the submucosal surface of the inner circular muscularis layer
- function = pacemaker and mediator of neuromuscular transmission
What are the 2 major functions of the colon?
- absorb water and electrolytes
- storage of feces
How is water absorbed in the large intestine?
- absorbs 90% of the water that comes in at the proximal large intestine
- mediated by aldosterone and glucocorticoids (stimulates Na/K ATPase)
- Na+ absorption is not linked to glucose and glucose containing fluids does not help with LI diarrhea
Mucin secretion is dependent on which electrolyte?
Cl-
What are the different rhythmic contractions that help with the functions of the large intestine?
- Absorption of water/ electrolyte in the proximal LI:
- rhythmic phasic contractions –> mixing of content and absorption of water
- retrograde giant contractions –> pushes the contents towards the cecum - Evacuation of feces in the distal LI:
- giant migrating contractions
How is short chain fatty acids (SCFA) made in the large intestine? Why is it imporant?
- SCFA the product of metabolism of carbohydrates, proteins, and lipides, done by the colonic microflora.
- the SCFA is then metabolized by the colonocytes to:
a. provide important energy to the LI epithelium
b. promote proliferation and differentiation of the colonocytes
c. modify colonic motility
How does butyrate produced by the colonic modify the immune system?
can induce anti-inflammatory cytokine such as IL-10
What’s M cells?
M cells = microfold cells
- found in the epithelium overlaying that lymphoid follicles
- contains dendritic cells
- activates the adaptive immune system
Is full thickness colonic biopsy recommended?
No
What’s the pathophysiology behind frequent defecation and tenesmus in large bowel diarrhea?
colitis has direct effect on colonic motility
- decreases non-propulsive smooth muscles cells, increases giant migrating contraction
What’s the most common histologic form of colitis?
lymphoplasmacytic colitis
- eosinophilic less common
- pyogranulomatous is uncommon
What’s the histological features of granulomatous colitis?
presence of macrophages full of periodic-acid-schiff (PAS)-positive staining material underlying an ulcerated colonic mucosa
What’s the most common signalment for granulomatous colitis?
young dog, Boxer
- severe, chronic, LI diarrhea
- hematochezia, increased frequency of defecation, tenesmus, excessive mucus in feces
Which type of colitis is more common in the Boxers?
lymphoplasmacytic colitis
What’s the treatment for granulomatous colitis?
enrofloxacin
What can Clostridium perfringens produce that lead to colitis?
Toxin A = major toxin A and enterotoxin
- but they can be found in healthy animals
- so evidence of sporulation or PCR (+) does NOT equate to infection
Which E. coli has tropism for the large intestine?
EHEC - enterohemorrhagic E. coli
- produces Shiga-like toxins (verocytotoxicin, cytotoxic necrotizing factors 1 and 2)
What’s the pathogenesis of EHEC?
Shiga-like toxins (verocytotoxicin, cytotoxic necrotizing factors 1 and 2)
- kills colonocytes via inhibition of protein synthesis –> edema, submucosal hemorrhage, arteritis, and arteriolar thrombosis
Which parasite causes ulcerative colitis in dogs?
Balantidium coli
Which protozoan is an important one for feline colitis?
tritrichomonas foetus
What’s the clinical presentation of tritrichomonas foetus infection?
- mostly in young (<1y) kittens
- catteries, shelters, multi-cat household
- waxing/waning large bowel diarrhea - mucoid, hemorrhagic, foul smelling
- can recur when stressed out
How is tritrichomonas foetus diagnosed?
- fecal exam (don’t confuse with Giardia)
- best to use diarrhea or high-colonic wash samples
Which is the most sensitive method for diagnosing tritrichomonas foetus?
PCR
What’s the treatment for tritrichomonas foetus?
Ronidazole
- may also spontaneous resolve (in 9m)
What’s the causative organism of schistosomiasis in dogs?
Heterobilharzia americana
What are the clinical signs of schistosomiasis in dogs?
- vomiting
- large bowel diarrhea
- hematochezia
- the fluke penetrates the skin, migrates through the lungs/ liver/ penetrate the intestinal mucosa (marked granulomatous reaction)
- can have hypercalcemia!
Which helminth can have hyponatremia and hyperkalemia as seen in hypoadrenocorticism?
Trichuris spp.
What are some clinical signs of Trichuris spp. infection?
- abdominal pain
- weight loss
- vomiting
- hematochezia
- diarrhea
What’s the most common cancer in the canine large intestine?
adenocarcinoma, lymphoma
What’s the most common cancer in the feline large intestine?
adenocarcinoma, lymphoma
In which species (feline vs canine) does colonic adenocarcinoma have a higher rate of local metastasis?
cats!
Where is the most common location for adenocarcinoma in cats?
ileal > colonic
but if in colon, descending > ileocolic
What’s the most common presenting signs for GI adenocarcinoma in cats vs dogs?
Cats tend to be more proximal - so hematochezia, rather than obstruction/ constipation is more common than dogs
What’s the preferred method of diagnosing GI adenocarcinoma?
flexible colonoscopy with mucosal biopsy
What are the clinical signs associated with ceco-colic intussusception?
- hematochezia
- may have diarrhea
- abdominal pain
- palpable abdominal mass
- not reported in cats (much shorter cecum than the dog)
What is associated with neurogenic colonic ulceration?
IVDD or after spinal surgery
- very rare
Which type of entero-colic intussusception is most frequently encountered?
Ileo-colic
What are the clinicals signs of intussuception?
- intermittent vomiting
- progressive loss of appetite
- mucoid bloody diarrhea
- abdominal pain = inconsistent finding
What’s the best way to diagnose an intussusception?
AUS!
- target-like mass (2+ hyperechoic/ hypoechoic rings)
What’s the treatment for intussusception?
reduction or R & A, but hopefully can preserve the ileo-ceco-colic junction to minimize risk of reflux/ fecal contamination of the ileum.
Recurrence 11-20%
What’s the main clinical sign of IBD in dogs?
mucoid diarrhea, and tenesmus
can have hematochezia
How is chronic idiopathic large bowel diarrhea treated in dogs?
aka “IBD”
- highly digestible diet
- anxiolytics and antispasmodics
What are some signs associated with obstipation?
- vomiting
- decrease in appetite
- dehydration
What are the 2 types of megacolon?
dilated vs hypertrophic
What’s the etiology of hypertrophic megacolon and how is it treated?
Due to a stricture (ex. malunion of pelvic fracture)
- early intervention (ex. correcting the pelvic narrowing) can have full resolution
- otherwise may progress to irreversible dilated megacolon
What’s the etiology of dilated megacolon?
Due to secondary electrolyte abnormalities, neuromuscular disorders, or idiopathic
Which electrolyte abnormalities can lead to megacolon?
hypokalemia
hypercalcemia
What’s the more common cause of megacolon in dogs?
- enlarged prostate
- perineal hernia (female)
What other clinical signs would be present for megacolon cats due to neurogenic cause?
signs of dysautonomia
- regurgitation
- prolapsed 3rd eyelid
- bradycardia
- urinary retention
- decreased lacrimation
- mydriasis
What are some treatment options for megacolon?
- removal of impacted feces
- oral/ suppository laxative
How does lactulose work for constipation?
- it’s an hyperosmolar laxative
- the fermentation production helps with colonic fluid secretion and propulsive motility
What is the most effective stimulate laxative in the cat? how does it work?
Bisacodyl
- stimulated nitric oxide mediated epithelial cell secretion and myenteric neuronal depolarization
