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) Amphioxus - a close relative of 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  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 Proteins Fats CHO Vitamins Minerals 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 quiz Omnivore, 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.