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
