Understanding Animal Digestive System

Animal, Plant & Soil

Science

Lesson C3-2

Animal Digestion

Objectives

� Identify the various types of digestive systems found in animals.

� Identify the major parts of the digestive system and describe their functions.

What are the various types of digestive systems found in animals?

� Knowledge of the different types of digestive systems is critical in selecting the proper feeds for livestock.

� Understanding the chemical and physical changes that occur during the digestive process leads to more efficient livestock feeding.

� Digestion is the process of breaking down food into simple substances that can be absorbed by the body.

� Absorption is the process of taking the digested parts of food into the bloodstream.


� The digestive system consists of the parts of the body involved in chewing and digesting food. � This system also moves the digested food through the

animal’s body and absorbs the products of digestion. � Different species of animals are able to digest certain types

of feeds better than others. � This difference occurs because of the various types of

digestive systems found in animals.

� There are four basic types of digestive systems: monogastric (simple), ruminant (polygastric), pseudo-ruminant, and avian.


� A. The monogastric digestive system, or simple digestive system, contains a single-chambered stomach and is the type found in humans, swine, dogs, and cats. � The stomach is a muscular

organ that stores ingested food and moves it into the small intestine.


� The stomach secretes acid that has a low pH of 1.5 to 2.5.

� The low pH destroys most bacteria and begins to break down the food materials.

� Animals with this type of digestive system are better adapted to the use of concentrated feeds, such as grains, than to the use of large quantities of roughages.



� B. The ruminant digestive system, or polygastricdigestive system, contains one large stomach divided into four compartments and is the type found in cattle, sheep, and goats. � An animal with this kind of digestive system is called a

ruminant. � Due to the complexity of its digestive system, a ruminant

can make good use of roughages. � Forty-four percent of the roughages fed are digested. � The compartments of the stomach, in the order of

digestion, are rumen, reticulum, omasum, and abomasum.


� 1. The rumen is the largest section of the stomach and the first compartment that the food enters. � It accounts for approximately 60

percent of the stomach.� The rumen contains bacteria and

other microbes that promote fermentation.� The rumen is designed so that food can be

ingested, eructated (belched up), chewed, and then swallowed again.


� 2. The reticulum is the second segment of the stomach. � It is sometimes considered an extension of the

rumen. � The reticulum has honeycomb-like ridges. � It aids in keeping the food in the rumen mixed with

water and saliva until it is the right consistency. � Once the right consistency is reached, the mixture

can pass on into the lower digestive tract.


� 3. The omasum is a small compartment that is the main sight for water absorption.� The particles are squeezed and dehydrated, as

well as sorted. � The compartment acts as a filter for the

abomasum.


� 4. The abomasum, or “true stomach,” is the site of digestion. � It secretes gastric juices consisting of hydrochloric

acid and pepsin. � These juices kill and then digest the microbes that

have passed with the food materials from the rumen.

� The abomasum is similar to the stomach in a monogastric animal.


� C. The pseudo-ruminant digestive system is the type found in animals that eat large amounts of roughages but do not have stomachs with several compartments. � This type of digestive system

performs some of the same functions as the type found in ruminants.


� A pseudo-ruminant can utilize large amounts of roughages because of its greatly enlarged cecumand large intestine.

� Such an animal often eats forages as well as grains and other concentrated feeds.

� Examples of pseudo-ruminants are horses, rabbits, guinea pigs, and hamsters.


� D. The avian digestive system is the type found in poultry. � This system differs greatly

from any other type. � Since a bird has no teeth,

no chewing is involved. � The esophagus empties

directly into the crop.


� The crop is where the food is stored and soaked. � From the crop, the food makes its way to the

gizzard. � The gizzard is a very muscular

organ, which normally contains stones or grit that grinds the food.

� Digestion in the avian system is very rapid.

What are the major parts of the digestive system and their functions?

� The digestive system is made up of a number of organs, which are parts that perform specialized functions.

� The digestive system begins at the mouth, where food enters the body, and continues to the anus, where undigested material exits the body.

� The digestive systems of most livestock are very similar in terms of the organs they contain.

� Some of the major parts of a digestive system and their functions are:


� A. Mouth and esophagus—The chewing action of the mouth and teeth breaks, cuts, and tears up the food. � This increases the surface area of the

food particles and aids in the swallowing process.

� Saliva not only stimulates the taste of the food but also contains the enzymes salivary amylase and salivary maltase.


� Enzymes are organic catalysts that speed up the digestive process.

� Salivary amylase changes starch to maltose, or malt sugar.

� Salivary maltase changes maltose to glucose.� Chewed food passes from the mouth to the

stomach through a muscular tube called the esophagus.


� B. Monogastric stomach—When food enters the stomach of a monogastric animal, gastric juices begin to flow. � The fluids come from

glands in the wall of the stomach.

� The juices contain from 0.2 to 0.5 percent hydrochloric acid.

� This acid stops the action of the amylase from the mouth.


� The gastric juices also contain the enzymes pepsin, rennin, and gastric lipase.

� Pepsin breaks the proteins in the food into proteoses and peptones.

� The muscular walls of the stomach churn and squeeze the food.

� Liquids are pushed on into the small intestine. � The gastric juices then act on the solids that

remain in the stomach.


� C. Ruminant stomach—The four parts of the ruminant stomach are rumen, reticulum, omasum, and abomasum. � A ruminant typically eats

rapidly. � It does not chew much of

its food before swallowing. � The solid part of food goes

into the rumen.


� The liquid part goes into the reticulum, then into the omasum, and on into the abomasum.

� In the rumen, the solid food is mixed and partially broken down by bacteria.

� When the rumen is full, the animal lies down. � The food is then forced back into the mouth, and

rumination occurs. � Rumination is the process of chewing the cud. � The cud is a ball-like mass of food brought up

from the stomach to be rechewed.


� On average, cattle chew their cuds about six to eight times per day.

� Five to seven hours each day are spent in rumination.

� The rumen and the reticulum contain millions of bacteria and protozoa. � It is the bacterial action in the rumen that allows a

ruminant to use large amounts of roughage. � The bacteria can change low-quality protein into

the amino acids needed by the animal.


� Amino acids are compounds that contain carbon, hydrogen, oxygen, and nitrogen.

� They are essential for growth and maintenance of cells.

� Bacteria also produce many of the vitamins needed by the animal.


� D. Small intestine—The partly digested food that leaves the stomach enters the small intestine as an acidic, semifluid, gray, pulpy mass.

� This material is called chyme. � In the small intestine, the chyme

is mixed with three digestive juices: pancreatic juice, bile, and intestinal juice.


� 1. Pancreatic juice, secreted by the pancreas, contains the enzymes trypsin, pancreatic amylase, pancreatic lipase, and maltase. � Trypsin breaks down proteins not broken down

by pepsin. � Some of the proteoses and peptones are broken

down by trypsin into peptides. � Proteoses, peptones, and peptides are

combinations of amino acids.


� Proteoses are the most complex compounds, and peptides are the simplest.

� Pancreatic amylase changes starch in the food into maltose.

� Sugar and maltose are broken down even further by maltase.

� They are then changed into a simple sugar called glucose.

� Lipase works on fats in the food, changing them into fatty acids and glycerol.


� 2. Bile is a yellowish-green, alkaline, bitter liquid produced in the liver. � Bile is stored in the

gallbladder in all animals except the horse.

� Bile aids in the digestion of fats and fatty acids.

� It also aids in the action of the enzyme lipase.


� 3. Glands in the walls of the small intestine produce intestinal juice. � Intestinal juice is a fluid that contains peptidase,

sucrase, maltase, and lactase, all enzymes used in digestion.

� Proteoses and peptones are broken down by peptidase into amino acids.

� Starches and sugars are broken down by sucrase, maltase, and lactase into the simple sugars glucose, fructose, and galactose.


� E. Cecum—The cecum, or “blind gut,” is found where the small intestine joins the large intestine. � It has little function in

most animals. � In a pseudo-ruminant,

the roughages consumed are digested by the bacterial action in the cecum.


� F. Large intestine—The main function of this organ is to absorb water. � Material not digested and absorbed in the small

intestine passes into the large intestine. � The key to absorption in the large intestine is the

small fingerlike projections on the walls, called villi.


� Food materials not digested or absorbed are called feces.

� These materials are moved through the large intestine by muscles in the intestinal walls.

� The undigested part of food is passed out of the body through the anus, the opening at the end of the large intestine.

Review

� What are the various types of digestive systems found in animals?

� What are the major parts of the digestive system and their functions?

Understanding Animal Digestive System

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