Comparative Vertebrate Digestion

The Veterinary Student Outreach Program

Basic Vertebrate Gut Anatomy Vertebrate body plan – a “tube

within a tube” The role of a digestive tract

Take in foods (ingestion) Break into simple molecules (digestion) Absorb nutrients (absorption) Eliminate waste/indigestible items

(egestion)

Am

ph

ioxu

s - a close relative o

f vertebrates

Human digestive system

The major subdivisions Oral cavity Pharynx Esophagus Stomach Small and large

intestine Rectum Anus

Human digestive system

Accessory organs Tongue Teeth Salivary glands Liver Gall Bladder Pancreas

Variations on a theme Humans are classic omnivores

made for digesting a little bit of all sorts of foods. Other animals are more specialized to digest

specialized types of diets

Shark Bird Rabbit/Horse Cow

Digestive Anatomy and Diet

Differences between vertebrate GI tracts often based on diet Easily absorbed food (hummingbird) versus food

requiring extensive digestion (carnivore) Constant food supply (herbivore) versus scattered

food supply (carnivore) High fiber food (herbivore) versus low fiber

(carnivore, frugivore)

Today’s Goals

Learn a little about animal nutrition Compare some different digestive systems to

look for general principles Observe how form and function fit together Look at some neat gross anatomy specimens

and histology slides

Our example species for today…

Animal Nutrition – Nutritional Categories Carnivore

Concentrated diet Easily digested Low fiber High protein and fat

Herbivore Low concentration of

nutrients Harder to digest High fiber Low protein and fat

Omnivore = consumes mixed diet; human, pig, many birds and primates

Carnivore Diet

Primarily meat based Water Protein Fat Carbohydrates Vitamins Minerals

Carnivore GI tract

“Monogastric” Simple structure Long small intestine for

digestion and absorption of fats and proteins

Retains basic tubular structure

Carnivores:

Proteins

Fats

CHO

Proteins

Fats

CHO

Vitamins

Minerals

Fiber

Ruminant GI tract Fore-gut fermenter Has complex stomach consisting

of: Rumen Reticulum Omasum Abomasum

Four-part stomach – not four stomachs!!

Relatively more complex colon and cecum for storing non-digestible fiber

Ruminant Herbivore Diet

Hay, silage, forage, grass, oats

Can digest plant material due to their complex stomachs

Stomach acts as fermentation vat

Ruminants:

Proteins

Fats

CHO

VFA

Proteins

Fats

CHO

Vitamins

Minerals

Fiber

Rumination Rumination

reduces particle size of fiber exposes sugars to microbes microbes ferment diet

Eructation

Eructation = burping Fermentation produces gases that must be

released…. One way or the other… Burp or Die!

Equine/Rabbit GI tract

“Monogastric” Hind-gut fermenter Large investment in large

intestine and ceca (singular = cecum)

Digestion of grains in stomach and small intestine

Digestion of fiber in “hind-gut”

Hind-gut Fermenter Diet

Forage

Hay (or grass) Source of Energy, protein, vitamins, minerals, fiber

Oats Barley

Similar diet to ruminants, but different digestive strategy

Hind-gut Fermenter

ProteinsFatsCHOVitaminsMinerals Fiber

CHO

Fibers – Digestible and Non-digestible Fiber = Coarse, indigestible plant matter, consisting

primarily of polysaccharides such as cellulose, that when eaten stimulates intestinal peristalsis. Usable or digestible fiber is needed for energy for the

microorganisms in the horse’s cecum and large intestine Indigestible fiber is required for the maintenance of normal

gastrointestinal pH, motility and function Grain is supplemental to provide sugars, proteins

and some fats

Birds – an anatomy/nutrition pop quizOmnivore, Carnivore or Herbivore?

Mice, rats, birds, insects

1. Carnivore

Fruits, grains, insects, seeds

2. Omnivore

Leaves

3. Herbivore

Fruits, flowers, insects, seeds, green vegetation.

4. Omnivore

Seeds, grasses, bushes, small invertebrates

6. Herbivore

Fruits, flowers, insects, seeds, green vegetation.

5. Omnivore

And now for some hands on activity… If you want to touch you will need gloves. Split into four groups and dive in!! Ask the vet students to show you the major

structures Be gentle – these are educational specimens! If you get grossed out, that’s OKAY! Grab a

stool and sit down for a few minutes – we don’t want anyone to get hurt.