33 LI activity and function

LI Activity and Function


As described previously, the large colon is often modified across species. Carnivores have a relatively short colon.


The main roles of the large intestine are

  • remove water and salt (although the SI does more of this)
  • move ingesta along the GI tract
    • rectum: store and expel waste products
  • maintain a healthy microbiome
    • fermentation/cellulose digestion in some species

Water removal

The large intestine is responsible for additional water removal and microbial nutrient production.

Ingesta movement

Large intestinal activity includes segmentation, some reverse peristalsis and mass movements – coordinated long contractions that move the ingesta toward the anus.

Goblet cells produce mucus to help with propulsion of the ingesta.


The microbiome helps with immune function, keeps out other bad bacteria and produce essential B vitamins, vitamin K, volatile fatty acids and nitrogen (through self-sacrifice).

The short chain fatty acids provide energy to the host and help maintain gut health and the barrier function, primarily by supporting goblet cell mucous production.

Bacteria prevent the proliferation of pathogenic bacteria in the gut and support immune cell function by producing the short chain fatty acids and by producing secondary bile acids.

The microbes do ferment feedstuffs in all of us – not just ruminants. Particularly when we eat nonsoluble fiber and difficult to digest foods.

Fecal production

Animal feces vary drastically by species and individual. In general, species that live in arid environments with minimal access to fresh water tend to have drier stool. Wombats do have squarish shaped poo (story here). In general variations occur between species due to differences in GI tract differences:
  • length
  • fore/hindgut fermentation
  • activity differences
  • microbial populations
  • absorptive capability

Variations between individuals occur due to differences in:

  • Diet – affects transit time and secretions
  • Stress levels
  • Hydration
  • Drugs or other disorders


Key Takeaways

The large intestine is responsible for residual water and salt absorption, fermentation, vitamin production and absorption and storage/expulsion of waste products.



The role of the canine microbiome and metabolome, 2020 Frontiers in Vet Sci

2021 Rethinking Our Approach to Diarrhea – Jen Granick, MVMA

Just for fun

I am called your large intestine


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Vet Med: Applied GI Physiology- Supplemental Notes Copyright © by Erin Malone DVM PhD is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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