digestive system classifications

VTS 150VTS 150Animal NutritionAnimal Nutrition

Fall 2010Fall 2010

Instructor: Beth Alden, DVM

Course ObjectivesCourse Objectives

Understanding of different digestive systems

Learn the nutritional needs of small companion animals, “pocket pets,” large animals and exotic pets

Learn about nutritional diseases for several species

Learn how to calculate an animal’s energy needs

Know how to evaluate a pet food label and ingredients

Learn common toxicities for dogs and cats

Resources for ClassResources for Class

TextbookTextbook:

Nutrition for Veterinary Technicians and Nurses, Ann Wortinger,Blackwell Publishing, 2007

Resources on Library Resources on Library ReserveReserve

Small Animal Clinical Nutrition 4th Edition, Hand,Thatcher, Remillard, Roudebush, The Mark Morris Institute, 2000

What’s Required of You:What’s Required of You:

2 Unit ExamsThree (3) Student ProjectsFinal Exam

Digestive System

Classifications

Digestive ClassificationsDigestive Classifications

Two Methods of Digestive System Classification

Food Source Stomach Type

Herbivores: Plant eaters

Carnivores: Meat EatersOmnivores: Plant and Meat Eaters

HerbivoresHerbivores

Plant material makes up diet• Rough vegetation, nitrogen source, minerals &

water

Difficult to digest• Plant cell wall is hard to break down • Energy from the plant is tied up in cellulose that

animal cannot digest on its own• The animal has developed a large complex gut to

digest this material• Microbial action in gut is necessary to break down

the cellulose and release its energy• Little of the food’s energy is absorbed by host

CarnivoresCarnivores

Animal material (flesh, muscle, etc.) makes up diet

Food more easily digested than in herbivores

The animal has a very simple “gut “

Most of food’s energy is absorbed by host

Mechanical breakdown of food is less involved

Types of Digestive SystemsTypes of Digestive Systems

Four compartment stomach:

Reticulum, Rumen, Omasum & Abomasum

(cows, sheep, goats)

One “true” stomach

(dogs, cats, pigs, horses)

RuminantMonogastric

Monogastric AnimalsMonogastric Animals

The Monogastric StomachThe Monogastric Stomach

Five sections:

◦Cardia◦Fundus◦Body◦Antrum◦Pylorus

Source: University of California at Davis


1. Cardia Area immediately

surrounding the opening from the esophagus into the stomach

Muscular tone prevents reflux of stomach contents into the esophagus


CARDIA


2. Fundus◦ Located below

the cardia

◦ Blind pouch that distends as food is swallowed


FUNDUS

CARDIA


3. BodyDistends to receive foodRich with gastric glands

Parietal Cells:Hydrochloric acid (HCl)

Chief Cells: Pepsinogen

Mucous Cells: Mucus

BODY


FUNDUS

CARDIA

BODY


4. AntrumGrinds up food and

regulates HCl

Also contains glands

BODY


FUNDUS

CARDIA

BODY

ANTRUM

G Cells: Gastrin

Mucous Cells: Mucus


5. PylorusMuscular ring

(sphincter)

Regulates movement of chyme from stomach into duodenum

Helps prevent backflow of duodenal contents

BODY


FUNDUS

CARDIA

BODY

ANTRUM

PYLORUS

DUODENUM

Ruminant AnimalsRuminant Animals

The Ruminant AnimalThe Ruminant Animal

Chews and swallows its food then regurgitates “cud” to chew on it more before swallowing again

Has a “prestomach” configuration that is adapted to the herbivore diet

Four compartment stomach

The Ruminant StomachThe Ruminant Stomach

Four Compartments:

◦Reticulum

◦Rumen

◦Omasum

◦AbomasumSource: University of California at Davis

head tail


head


1. The Reticulum

Smallest, most cranial compartment

Separated from rumen by the ruminoreticular fold

Muscular wall is continuous with the rumen; contract in coordination

tail

RETICULUM


1. The Reticulum

Honeycombed inside to increase absorptive surface

“Hardware disease”- wires or nails swallowed by animal puncture wall of reticulum

Inside of Reticulum

Source: Colorado State University

RETICULUM


2. The Rumen

Large fermentative vat(40 - 50 gallon capacity)

Processes plant material into usable energy

Lined with “Papillae”

Made up of series of muscular “Pillars”


head tail

RUMEN


© University of Bristol, 1988

Pillar PapillaePapillae


2. The Rumen

During contractions, pillars close off certain sacs of the rumen which allows mixing of ruminal contents

Mixing of contents essential for fermentative function of rumen

RUMEN


What reticuloruminal contractions do:1. Allow “cud” to be regurgitated up the

esophagus, where it’s re-chewed and re-swallowed

2. Allow “eructation” - built-up CO2 or

methane gas to be expelled from rumen. Gasses are forced into the reticulum and up the esophagus

RUMEN


Fermentative digestion begins in the rumen

Bacterial and protozoal enzymes break down foodstuffs

Carbohydrate Metabolism:◦Cellulase enzymes digest cellulose (plant cell

layer) and transform complex carbohydrates into simple sugars

◦ Simple sugars aren’t made available to host (like they are in monogastric animals), instead are absorbed into the microbes and converted to Volatile Fatty Acids (VFAs)

RUMEN


Carbohydrate Metabolism, continued

- Volatile fatty acids are by-products of anaerobic fermentation by bacteria in rumen

Some VFAs absorbed into liver then converted to glucose, which is used by the animal’s cells

Other VFAs are used to produce adipose tissue and milk fat

RUMEN

The Ruminant StomachThe Ruminant StomachProtein Metabolism:Rumen microbial enzymes attack

proteins (just like carbohydrates)

Proteases reduce long proteins to amino acids and short peptides (short chains of amino acids)

Peptides are either incorporated into the protein structure of the microbes OR converted to ammonia (NH3

+) and VFAs

RUMEN


Protein Metabolism, continued

Liver secretes urea* into the rumen, which provides additional nitrogen for the microbes

Microbes are then flushed from the reticulorumen to the omasum, abomasum and intestines; digested and serve as source of protein to the animal

* Urea is sometimes added to poor-quality

feed as a way of increasing nitrogen

value

RUMEN


Other Notes about the Rumen

Provides B vitamins; Vitamin K

Delicate balance: amount of food, growth of microbes and by-products

Changes in diet severely affect production of gas, VFAs and ammonia, causing fermentation process to completely stop

RUMEN


3. Omasum

Muscular organ located off the reticulum

Ingesta moves into omasum from reticulorumen

Prevents large particles from leaving rumen and entering abomasum

OMASUM


head tail


3. OmasumPrimary functions◦Break down food particles

further and move ingesta to abomasum

◦Absorb any excess VFAs

◦Remove bicarbonate ions from ingesta (to avoid altering acid pH of abomasum)

OMASUM


4. Abomasum

“True stomach” of ruminant

Functions similar to monogastric stomach

ABOMASUM


head tail

Young Ruminant Digestive Young Ruminant Digestive TractTract

Functions as a monogastric system

No fermentative digestion (rumen & reticulum are non-functional)

Reticular groove or Esophageal groove allows suckled milk to go to omasum

Suckling is important – helps groove to function

Bucket–fed calves spill milk into rumen & reticulum

Young Ruminant Digestive Young Ruminant Digestive TractTractAbomasum is largest of 4

stomachs for the first few weeks

Rumen & reticulum development rate dependent on diet:

◦Grain & Hay fed – develop at 3 weeks◦Milk fed – develop at 3 months

Chronology of Digestive Chronology of Digestive SystemSystem

GI tract extends from mouth to the anus and performs different functions at different parts

Chronology of Digestion: Prehension Mechanical grinding down of food Chemical digestion of food Absorption of nutrients and water Elimination of waste material

Chronology of DigestionChronology of Digestion1. Prehension1. Prehension

Grasping food with teeth or

lips

Chronology of DigestionChronology of Digestion::2. Mechanical Grinding Down of 2. Mechanical Grinding Down of FoodFood

Carnivore TeethPointed to facilitate holding and tearing of food

© Clinical Textbook for Veterinary Technicians 6th ed.; McCurnin, Bassert

Chronology of Digestion:Chronology of Digestion:2. Mechanical Grinding Down of 2. Mechanical Grinding Down of FoodFood

Herbivore TeethFlat, occlusal surface for grinding


Incisors – Teeth in the front for holding and tearing

Canines – Pointed teeth located at corners for tearing and shredding

PremolarsPremolars – Located just before the molars and are used for grinding in all species

MolarsMolars – Used for grinding

Ruminant TeethNo upper incisors or upper canine teeth


Dental PadDental Pad

ThickThickconnectiveconnective

tissuetissue

DiastemaDiastema

Chronology of Digestion:Chronology of Digestion:2. Mechanical Grinding Down of Food2. Mechanical Grinding Down of Food

Positional Location of Teeth - Terminology

MaxillaMaxilla Upper Arcade

MandibleMandible Lower Arcade

LingualLingual Inner side of lower arcade teeth that face tongue

LabialLabial Outer surface of upper and lowerarcade teeth (faces lips)

PalatalPalatal Inner side of upper arcade teeth(faces the palate)

BuccalBuccal Outer side of teeth in back of mouth (faces the cheeks)

Chronology of Digestion:Chronology of Digestion:3. Chemical Digestion of Food3. Chemical Digestion of FoodSaliva mixes with food during chewing

Three bilateral pairs of salivary glands in the mouth (parotid, mandibular, lingual)

What saliva does:◦ softens, moistens, shapes & lubricates

food◦ aids in taste◦ acts as a buffer◦ provides digestive enzymes

Chronology of DigestionChronology of Digestion3. Chemical Digestion of Food3. Chemical Digestion of Food

Digestive enzymes and buffers in saliva

Amylase: in omnivore saliva – not carnivore breaks down amylose (sugar component of starch)

Lipase: breaks down lipidsBicarbonate and Phosphate buffers:

in cow saliva; neutralizes acids inrumen & maintain normal rumen pH ( up to 25-30 gallons of saliva a day)


EpiglottisEpiglottis •Cartilage projection

that prevents food from entering trachea

EsophagusEsophagus - transports food to

stomach•Peristalsis: smooth

muscle contractions to propel food


StomachStomach Stores food

Continues enzymatic breakdown of food (pepsin, gastrin, hydrochloric acid)

Mechanical breakdown of food (mixing, grinding and contractions that move food)

Ruminants: each compartment has different function


LiverLiverSecretes bile acids to help with digestion of fat

PancreasPancreasSecretes enzymes into small intestine for breaking down nutrients:

Protease for proteinsAmylase for carbohydratesLipase for fats/lipids

Also secretes bicarbonate to neutralize stomach acid

Chronology of DigestionChronology of Digestion4. Absorption of Nutrients & 4. Absorption of Nutrients & WaterWater

Small IntestineSmall Intestine◦Duodenum, Jejunum, Ileum

◦Inner & sub mucosal layer; Muscular layer

◦Villi & Microvilli increase surface area in intestine

◦Peristaltic waves help move contents through intestines

Chronology of DigestionChronology of Digestion4. Absorption of Nutrients & Water4. Absorption of Nutrients & WaterSmall IntestineSmall Intestine

◦ No clear demarcation between 3 segments

◦ All 3 segments perform peristalsis, absorb nutrients & H2O

Duodenum: first portion of sm. intestine

Jejunum: majority of sm. intestine

Ileum: where sm. intestine enters colon


Villi◦ Millions of cylindrical, fingerlike projections

in intestinal wall◦ Provide large surface area for absorbing

nutrients◦ “Crypts” surround villi and replenish cells

Microvilli “brush border”◦ Found on Villi; contain digestive enzymes

• Transmissible Gastroenteritis (TGE) in pigs• Parvo Virus in dogs attack the villus

Animal cannot absorb nutrients from intestinal tract


Small Intestine◦Absorbs electrolytes

(Na, Cl, K, etc.); water and vitamins across intestinal wall

◦Absorbs carbohydrates, fats, proteins after they’re chemically digested via enzymes

Chronology of DigestionChronology of Digestion4. Absorption of Nutrients & 4. Absorption of Nutrients & WaterWaterNutrient digestion in the small

intestine

Carbohydrates:Carbohydrates: digested by amylase secreted from

pancreas

Protein:Protein: digested by proteases secreted bypancreas

Fat:Fat: digested by bile acids from liver (helps emulsify fat to prevent glob formation); further broken down by lipase secreted from pancreas

Chronology of DigestionChronology of Digestion5. Elimination of Waste Material5. Elimination of Waste Material

Large Intestine: Cecum & Colon

◦Recover fluid and electrolytes

◦Store feces until elimination

◦Some microbial action

◦Differences between species, dependent on diet


ColonCecum “blind sac”

Carnivores

Simple, tubular, contracts to move feces through

Poorly developed

Herbivores*

Large bacterial population (microbes) for fermentation

More developed, larger than carnivore

*Horses are different


Colon & Cecum comprise the “Hindgut”

4 sections: cecum, ventral colon, dorsal colon, small colon

More highly developed than small intestine

Has greater capacity for fermentation

Unique digestion path; colonic impaction is mostcommon form of colic in horses


RectumRectum◦ Terminal portion of colon◦ Contains mucus-secreting

glands◦ Sensory receptors detect

stretching/distension andtriggers defecation

AnusAnus◦ Internal & External

sphincters allow controlled passage of feces

Next Week…Next Week…

Session 2:

Basic Nutrients

digestive system classifications

Education