L3 - The Digestive System 

Gastrointestinal Tract (GI)

  • Same thing as Digestive Tract
  • Digestive SYSTEM includes GI tract + other organs
    • Mouth
    • Stomach
    • Small Intestine (SI)
    • Large Intestine (LI)
    • Rectum
    • Anus

Need to Know Terminology for CHO

  • Solubility - Is the CHO soluble in aq enviro?
  • Digestibility - Host has the right enzymes to digest CHO?
  • Fermentability - Do gut bacteria have the enzymes to break the CHO?

{{SIMPLE SYSTEM W/O CAECUM{{

  • applies to humans, cats, dogs

Key Features

  • Monogastric (single) stomach
  • Non functional caecum
  • Hindgut fermenter
  • good for nutrient dense, low fibre diet
  1. Oral Cavity
  • Food is chewed + mixed with saliva
  • Salivary glands also initiate some digestion
    • a-amylase (CHO) + lingual lipase (Fat)
  • No protein digestion yet
  1. Stomach (Cardia, Fungus, Body, Antrum)
  • Can expand as you consume more food
  • pH is v acidic - HCL ~2
  • Food becomes chyme
  • Gastric glands secrete gastric juice + enzymes
  • Partial protein digestion
  • Muscle contractions to churn + move food along
  1. Small Intestine (duodenum, jejunum, ileum)
  • main site for nutrient absorption
  • Very large surface area
  • chyme is neutralized with bicarbonate
  • muscle contractions push food along
  • digestive enzymes released from pancreas + bile from gall bladder
  1. Large intestine (colon)
  • Most nutrients are already absorbed
  • contains billions of gut bacteria
  • Fermentation occurs here
    • bacteria breaks down CHO into SCFA (short chain fatty acids) or VFA (volatile fatty acids)
    • Water is highly absorbed

Anatomy of the SI

  • Kerckring Folds - large folds within the tissues

  • Villi (and Crypts) - Further folds in the big ones

  • Microvilli - Tinier folds on top of the villi

    • Contain the brush border system for maximum nutrient absorption

Nutrient Transport Mechanisms

Simple Diffusion (Passive)

  • Conc dependent, high to low
  • Small non polar molecules

Facilitated Diffusion (Passive)

  • Channels are used cause molecules are bigger (need help)
  • Ions

Active Transport (ATP)

  • Conc move opposite the gradient
  • Low to high
  • uses ATP

Gut Bacteria

  • Contains 10^2-10^12 - LOTS of bacteria
  • Not evenly distributed + as you go down
  • 1000:1 Anaerobic to Aerobic bc Large intestine is anaerobic
    • balanced pH
    • O2 level all influence # of bacteria
  • Diff ppl have diff species but the functions are the same
    • Some animals eat their poop to evenly distribute gut bacteria
  • Imp for fermentation of non digestible CHO

{{SIMPLE SYSTEM W/ FUNCTIONAL CAECUM{{

  • applicable to horses, rabbits and hamsters

Key Features

  • Psuedo-ruminant
  • Hindgut Fermenter (fermentation in large intestine)
  • Functional Caecum
  • All other regions function similar to monogastric system
  • Diet with large amounts of fodder and foraging (high fibre)

Functional Caecum?

  • Enormous hindgut filled with bacteria
  • SCFA provide 70% of total energy host needs
  • Site for vitamin production
    • Adult horses eat their poop to consumer vitamins
    • Young horses eat their poop to colonize gut with bacteria

Where Nutrients are absorbed

  • SI - Glucose, Fats, Protein
  • LI - Produce lactic acid if on high CHO diet (bad for horses), Some protein digestion, SCFA
  • Indigestible fibre goes completely through

Memorize

MULTIPLE SYSTEM: RUMINANT

  • Applicable to cattle, sheep, goats

Key Features

  • Large stomach divided into 4 regions

    1. Reticulum
    2. Rumen
    3. Omasum
    4. Abomasum

  • Highly suited for animals that eat a high quantity of fodder and forage plant materials

  • Foregut Fermentation

Ruminant Digestion

  • Sometimes referred to as reticulorumen (grouped)
  1. Reticulum
  • Can capture nutrients and trap foreign materials (wire, metal)
    • can cause hardware disease (too much need magnet to take it out)
  • Rich in bacteria fermentation
  1. Rumen
  • The largest section of the stomach
  • Rich in bacteria
  • Rumen papillae (+ SA) for absorption
  • A lot of nrg is created here SCFA
  1. Omasum
  • Reabsorption of water
  • Filters large particles
  1. Abomasum “True Stomach'“
  • Digestive enzymes and juices secreted (like normal stomach)

Ruminant Digestion

  • Fermentation takes place before entering the intestine (SI)
  • Nutrients produced by bacteria then become available for digestion and absorption by the host + bacteria
  • Rumination - Swallowing, regurgitating, and repeat (helps with digestion)
  • Eructation (belching) - Huge loss of energy, fermentation, methane gas

Pros and Cons of Ruminant System?

  • Pros

    • Produces vitamin b4 absorption = good
    • Can feed on low quality (with not a lot of N)
    • bc bacteria later can make all the AA b4 absorption

  • Cons

    • Methane gas loss (energy)
    • Fermentation creates heat - uncomfy for cow

AVIAN SYSTEM

  • Applicable to chicken, turkey, birds

Key Features:

  • Beaks and claws are imp for breaking up food for birds to swallow
    • no teeth!
  • Rapid Digestion
    • Birds can starve if deprived of food for even a short time (hours)
  1. Crop
  • Enlarged area of the esophagus
  • temp storage spot for food
    • may regurgitate for offspring or swallow for self
    • food is also softened
  1. Two Chambered Stomach
  • Proventriculus - Glandular Portion
    • HCl + Digestive Enzymes
  • Gizzard - Muscular Portion
    • has stones that grind + digest tough food
  1. Small Intestine
  • Same as other systems
  • nutrient absorption
  1. Ceca
  • Minor site of bacterial fermentation
  1. Large Intestine
  • Very small
  • Mainly connects small intestine to a component called Cloaca
  • Bit of storage for undigested material
  • Water absorption
  1. Cloaca
  • Where the digestive, urinary and reproductive systems meet