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ANIMAL SCIENCE

8646-E

THE DIGESTIVE SYSTEM

INTRODUCTION

The digestive system is a way for nutrients from the outside environment to get to various parts of the body. At itssimplest, the digestive system is a tube running from the mouth to the anus. This tube is similar to an assembly line,or more properly, a disassembly line. Its chief goal is to break down huge macromolecules (proteins,* fats, andstarches) that cannot be absorbed as they are into smaller molecules (amino acids, fatty acids, and glucoses) thatcan be absorbed by the circulatory system. The circulatory system then disseminates the smaller molecules throughoutthe body.

The functions of the digestive system include ingesting food, grinding food, digesting food, absorbing nutrients, andeliminating solid wastes. The digestive system changes food nutrients into compounds that are easily absorbed.These nutrients are used for energy, growth, and maintenance of body tissues.

Plant nutrients consumed by animals must break down to simpler compounds before they can be used. Differentspecies of animals have digestive tracts adapted to the most efficient use of the feed they consume. Thus, theanatomy and physiology of the digestive systems of herbivores, carnivores, and omnivores are all different.

* Underlined words are defined in the Glossary of Terms.

Animals that depend entirely on plants for food are herbivores. Examples are cows, sheep, horses, and rabbits.Animals that rely almost entirely on flesh for food are carnivores. Examples are cats and dogs. Omnivores areanimals that consume both flesh and plants. Examples are hogs, chickens, and humans.

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Some similarities occur in the composition of the walls of the digestive tract of various species. The walls includefour layers - epithelium, lamina propria, muscles, and visceral peritoneum. The epithelium is a mucous membranethat lines the digestive system. It is continuous with the external skin of the animal at the mouth and anus. The laminapropria is a thin layer of connective tissue supporting the epithelium in the intestines. The muscles of the digestivesystem are striated through the esophagus but smooth throughout the remainder of the digestive tract. The visceralperitoneum covers the digestive organs in the abdomen.

The average capacity of the digestive system varies among animal species. The capacity of the hog’s digestivesystem causes a hog, an omnivore, to adapt better to the use of concentrated feeds such as grains, but limitedamounts of forages can be included in the swine diet. The digestive system of the horse, a herbivore, is much largerthan that of the hog. It allows the horse to use large amounts of roughage in its diet because of a greatly enlargedcecum. However, the horse is a non-ruminant.

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Cattle and sheep, both herbivores andruminants, have large digestivesystems that can use large amounts ofbulky feeds, such as forages. Thesefoodstuffs provide cattle and sheepwith the nutrients necessary for bodymaintenance and production of milk,meat, and wool. The stomach of a1,200-pound cow may have acapacity for 300 pounds of feed.

The ruminant’s stomach consists offour compartments - reticulum,rumen, omasum, and abomasum (truestomach).

ANATOMY OF THE DIGESTIVE SYSTEM

The digestive tract extends from the lips to the anus. It includes the mouth, pharynx, esophagus, stomach, smallintestine, and large intestine. The salivary glands, liver, gallbladder, and pancreas are accessory glands of thedigestive system. The length and complexity of the digestive tract depends upon the species. In carnivores, the tractis relatively short and simple. In herbivores, it is much longer and more complex.

The stomach is relatively simple in some herbivores, such as rabbits and horses. However, the large intestine islarge and complex. In other herbivores, such as cattle, sheep, and goats, the stomach is large and complex.However, the large intestine is simple.

The primary functions of the mouth are grasping and grinding feed and mixing feed with saliva. The structures in themouth responsible for grinding food are the teeth. The incisor teeth are used for cutting or shearing food. Thepremolars and molars of animals are responsible for grinding feed. After an animal is born, it develops a set of milkor baby teeth. Permanent, or deciduous, teeth replace the milk teeth but at different ages depending on the animalspecies.

The tongue of an animal consists of a mass of muscle covered by a mucous membrane. The top surface of thetongue is covered with finger-like projections called papillae, which contain the taste buds. The tongue is used tograsp food in most animals. It also aids in the chewing process as well as in the formation of a bolus.

The purpose of the lips in horses and sheep is to grasp feed. The lips of swine and cattle are rigid and are usedprimarily for closing the mouth.

The cheeks of animals consist primarily of muscle lined with a mucous membrane. The purpose of the cheeks is toline up food with the teeth for consumption. Powerful muscles control the movement of the jaw. These muscles aidin the opening and closing of the jaw as well as movement of the jaw from side to side in chewing.

A hard palate serves as the roof of the mouth. It turns into a soft palate toward the rear of the mouth and divides thepharynx from the oral cavity. Salivary glands are common in the mucous membrane lining of the mouth, except onthe tongue, hard palate, and gums.

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Food that has been ingested and chewed then passes into the pharynx, a common passageway for food and air.Several structures open into the pharynx. They include the mouth, the nasal cavity, the larynx, the esophagus, andthe eustachian tubes from the ears. The pharyngeal muscles of the pharynx force food into the esophagus from themouth. The eustachian tubes allow air to move freely from the pharynx to the eardrum (tympanic membrane). Thisallows the pressure to equalize on either side of the eardrum. The muscles contract in a series, from the top to thebottom end of the pharynx, during swallowing. This shortens the pharynx and pushes the food into the esophagus.

The esophagus is a muscular tube connecting the pharynx to the stomach. It passes through the chest cavity andconnects with the stomach just after passing through the diaphragm. The walls of the esophagus contain two layersof striated muscles. These muscles run at right angles to each other with one layer running parallel with the esophagus.The muscles change into smooth, involuntary muscles in the bottom one-third of the esophagus of the horse. Thisoccurs just in front of the diaphragm in a hog. The muscles remain striated throughout the esophagus in cattle,sheep, and dogs.

The stomachs of non-ruminants (hogs, rabbits, and horses) consist of only one compartment, sometimes called thetrue stomach. The stomachs of non-ruminants are located just behind the diaphragm on the left side of the body.The sphincter muscle, or cardia, is located at the junction of the esophagus and stomach. The pylorus, anothersphincter muscle, is located at the bottom of the stomach. These two sphincter muscles control the passage of foodin and out of the stomach.

The area of the stomach increases greatly from the infolding of the epithelial lining of the stomach. The insides ofthese folds are gastric pits. The outer layer of the stomach contains glands. These glands empty digestive secretionsinto the gastric pits of the stomach. Cardiac glands are located at the beginning of the stomach. Pyloric glands arelocated at the end of the stomach. Gastric, or fundic, glands are located throughout the midsection of the stomach.The gastric glands produce hydrochloric acid and the enzyme pepsin and rennin.

As stated previously, the stomach of a ruminant contains four parts: rumen, reticulum, omasum, and the abomasum.For the first three stomach parts, their linings contain no glands. They soak the food and allow microbial digestionto take place. The reticulum is the forward most portion of the ruminant stomach. Its inner surface consists of manyinward folds that are honeycomb-like in shape. A groove, called the esophageal groove, extends from the cardia tothe omasum. It is capable of closing the entrance of the rumen and reticulum. Specifically, this causes consumedfood to bypass these two parts and travel directly to the omasum.

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The rumen has a very thick muscular wall and extends from the diaphragm to the pelvis. It fills most of the left sideof the abdomen. The rumen itself has two parts, a dorsal sac and a ventral sac. The dorsal (upper) sac is the largerof the two. The rumen's rumino-reticular fold segregates it from the other parts of the stomach. The floor of each ofthe rumen’s two sacs contains many finger-like projections called papillae. Each papillae many extend to onecentimeter in length. The wall of the rumen consists of two layers of smooth muscle. These muscles extend at rightangles to each other, similar to those of the esophagus.

The relative sizes of the four stomach compartments of the ruminant vary with age of the animal. In the newborn calfor lamb, the first three compartments represent less than 30% of the total capacity of the stomach. As the ruminantanimal grows, forages and grains are added to the diet. At that stage, the rumen begins to develop. Normally, therumen of calves becomes functional in six to eight weeks. Food normally passes first into the rumen. The rumenmakes up 80% of the total stomach capacity in the mature animal.

The omasum is round in its shape and contains muscular projections from its roof. The mucous membrane thatcovers the projections contains many small papillae. These papillae are responsible for grinding roughage. Theomasum is located to the right of the rumen and reticulum and close to the liver. The mucous lining forms many foldswhere the omasum joins the abomasum.

The abomasum is the only glandular stomach of ruminant animals. It is similar to the single stomach of non-ruminantanimals. The first three parts of the ruminant stomach compare to the beginning part of the non-ruminant stomach.The abomasum is under the omasum and extends to the rear on the right side of the animal's body. The pylorusmuscle is located at the connection of the abomasum and the small intestine, similar to the non-ruminant stomach.The epithelial lining and glands of the abomasum are the same as those in the stomach of non-ruminants.

The small intestine is the next part of the digestive system in animals. It is made up of three parts, the duodenum, thejejunum, and the ileum. The pancreatic duct from the pancreas and bile duct of the liver empty digestive juices intothe duodenum. The duodenum extends to the pelvic area along the lower right side of the animal. It crosses over tothe animal’s left side and turns back toward the animal’s head. It then joins the jejunum. The exact juncture of thejejunum and ileum is difficult to locate. For most domesticated animals, the end of the ileum joins the large intestine.

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The large intestine consists of the cecum, a blind pouch, and the colon, which ends in the rectum and anus. Thelarge intestine varies much more than does the small intestine of domestic animals. The size of the cecum is muchgreater in horses and rabbits than it is in other domestic animals. The cecum in these species is in the shape of acomma (,). It is located on the lower right side of the abdomen. The base extends from the pelvic area to just underthe sternum at the diaphragm. The ileum of the small intestine joins the cecum at the lower part of its inside curve.

The cecum is not nearly as pronounced in most domestic animals as it is in the horse and rabbit. The cecum alsobegins the large intestine of a hog. The point of entry of the ileum to the colon marks the division between the cecumand the colon. The beginning of the large intestine of a hog is coiled, similar to the small intestine. The large intestinethen extends forward along the right side of the abdomen to the diaphragm. Then, it turns left crossing the body andturns again back toward the animal’s rear. It then joins the rectum that ends at the anus. In ruminants, the colonextends forward and coils up in the connective tissue supporting the small intestine. It then crosses over to the leftside of the body, returns to the animal’s rear, and connects to the rectum.

The colon begins in the pelvic area. It extends forward on the right side of the floor of the abdomen until it reachesthe diaphragm. It then turns left in the shape of a horseshoe and extends toward the pelvic area. Here, the coloncoils, similar to the small intestine, except it is larger than for the small intestine. The colon then extends toward therear of the animal where it joins the rectum. Waste is eliminated through the anus.

The anatomy of the digestive system of poultry differs from other animals. Poultry do not have teeth to initiallybreak down consumed food. The glandular stomach of poultry is the proventriculus. Food is stored temporarily inthe crop before it travels to the proventriculus. The crop, an enlargement of the gullet, is where food is softened.Feed passes quickly from the proventriculus to the ventriculus, or gizzard, which crushes and grinds coarse feed.Grit and gravel accumulated during the life of the bird aids in this process.

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ANATOMY AND PHYSIOLOGY OF ACCESSORY DIGESTIVE ORGANS

An accessory organ of the digestive system is the salivary glands. They are in pairs and include the parotid,mandibular, and sublingual salivary glands. The parotid glands are located under the ears of animals. Their ductspass over the rear of the mandible to near the middle of the cheek. Here, the ducts penetrate the mucous membraneof the mouth and secrete saliva. The mandibular salivary glands are under and to the rear of the parotid glands.Their ducts pass in the middle of the mandibles and open into the mouth under the tongue. The sublingual salivaryglands are located under the mucous membrane around the outer sides of the tongue. They empty into the floor ofthe mouth.

According to the type of fluid they secrete, the salivary glands are classified as serous, mucous, or mixed. Theserous type secretes a clear, watery fluid. The mucous type secretes a thick, cloudy substance. This substanceserves as a protective coating to the mucous membranes of the digestive system. Mixed salivary glands secretebody mucous and serous fluids. The parotid and mandibular salivary glands secrete only the serous type of fluid.The sublingual salivary glands secrete mixed fluids. They are not as well defined as the other two types ofsalivary glands.

The pancreas is an elongated, somewhat lobe-shaped organ. It is located close to the beginning of the smallintestine and behind the liver. It has both exocrine and endocrine functions. The exocrine part is the largest andproduces digestive juices. These juices pass through the pancreatic duct and then empty into the beginning of thesmall intestine or duodenum. The endocrine part of the pancreas produces the hormone insulin. Insulin goes directlyinto the bloodstream.

The liver is a lobe-shaped organ just behind the diaphragm. It is usually on the right side of the body. The liverreceives its fresh blood supply from the hepatic artery. It is responsible for purifying the blood brought to the liverby the portal vein from the stomach, spleen, pancreas, and intestines. Liver cells assist in formation of blood. The

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liver also destroys exhausted red blood cells, which are picked up by the bile duct for expulsion from the body.Liver lobules in swine are much more dominant than those of other domestic animals. This is because connectivetissue that covers the liver is much heavier in swine than it is in other domestic animals.

With the exception of the horse, all domestic animals have a gallbladder. The gallbladder is a small sac-like organattached to the liver. The gallbladder empties waste, as bile, through the common bile duct into the duodenum. Bileis sent to the gallbladder by the liver through the hepatic duct, which joins the cystic duct of the gallbladder.

THE PHYSIOLOGY OF DIGESTION

Digestion is the conversion of feedstuffs into nutrients. Excreting unused food residues (fecal material) is alsopart of digestion. The digestive system and its accessory glands make digestion possible. Most feedstuffs aretoo complex to be used without digestive changes. Some exceptions are glucose, soluble salts, water, and a fewother nutrients.

The digestive processes are mechanical, chemical, and microbial actions. Mechanical activities include mastication(chewing), deglutition (swallowing), regurgitation, gastric and intestinal motility, and defecation. The actions ofenzymes and other substances produced and secreted by the digestive glands are chemical activities. The activitiesof bacteria and protozoa in the digestive tract of animals make up microbial action, which is especially important fordigesting roughages.

The actions of enzymes in the digestive process of non-ruminant animals are important. The use of microbiologicalaction to digest foods in most of these species is of less importance. However, in the horse and the rabbit, theaction of microorganisms in the cecum is important in digesting fiber.

Many microorganisms exist in the digestive compartments of the ruminant. The microorganisms break down thecellulose of plant cell walls, especially roughages. This breakdown gives the ruminant 60% to 80% of its energyneeds. The energy is in the form of volatile fatty acids. Most of this breakdown occurs in the rumen. Absorption ofthe energy is accomplished primarily through the rumen wall. Approximately 60% to 90% of digestion in ruminantsoccurs in the rumen.

The microorganisms in the digestive system of ruminants synthesize B-complex vitamins and essential amino acids.Microorganisms make these amino acids from other proteins that are deficient in one or more essential aminoacids. They also can obtain the amino acids from adequate protein sources. Ultimately, the microorganisms aredigested farther down the digestive tract by the ruminant animal. The lining of the rumen is composed of manypapillae that aid in absorption of nutrients. Large amounts of gases (methane and CO2) are produced in the rumen.These gases are expelled by belching or by absorption into the blood. If these gases accumulate, they may causean inflation of the rumen, resulting in bloat.

A gland, called the hypothalamus gland, controls an animal’s appetite. The level of glucose in the blood and theamount of feed in the stomach influence an animal's appetite. The environmental temperature (hot or cold) alsoaffects the appetite of an animal. The manner in which animals ingest, or eat food, varies, but in some way, involvesthe use of the lips, teeth, and tongue. Cattle primarily use the tongue to ingest food, while horses use the upper lip.With a cleft upper lip, sheep mainly use the incisor teeth and tongue to ingest food. Swine use the pointed lower lip,teeth, and tongue to eat. Poultry use the beak for this purpose.

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Chewing food, or masticating, aids the digestive process. It reduces food particle size so digestive juices have agreater surface area on which to act. Chewing mixes the food with saliva to make swallowing easier. In ruminants,remastication of large amounts of ingested food is important. After the ruminant has consumed large amounts offood, it can regurgitate the food as a bolus (cud) by the process of rumination. It then chews the regurgitated foodfor a second time. Because poultry have no teeth, the gizzard accomplishes the grinding and crushing process.

Enzymes are responsible for most chemical changes occurring in the digestion process. Various body cells makethese enzymes. The enzymes speed up the biochemical reactions of digestion. This occurs at regular body temperatureand does not use up the enzymes in the process. In hogs and horses, the enzyme ptyalin begins the digestion ofcarbohydrates for conversion into maltose and dextrin. The salivary gland secretes ptyalin. Mucin in the salivalubricates the food to make it easier to swallow.

The pancreas secretes the enzyme amylopsin into the beginning of the small intestine. Amylopsin aids in the digestionof starches and dextrins to form simpler dextrins and maltose. Another enzyme that helps with the digestion ofcarbohydrates is sucrase. It breaks down sucrose into glucose and fructose. Maltase breaks down maltose intoglucose. Lactase breaks down lactose into glucose and galactose. Enzymes have nothing to do with the actions ofmicroorganisms on cellulose in ruminants.

Protein digestion begins in the true stomach of several species of animals. The abomasum is the “true” stomach ofruminants. It is comparable to the true stomach of other mammals and the proventriculus in poultry. Cells in the truestomach produce hydrochloric acid that activates the enzymes pepsin and rennin. Pepsin and rennin are importantto protein digestion. Pepsin, which is located in the gastric juices, begins protein digestion. It breaks protein downinto simpler compounds called proteoses and peptones. In young nursing animals, the enzyme rennin aids in thedigestion of protein in milk. The pancreas secretes the enzymes trypsin, chymotrypsin, and carboxypeptidase intothe duodenum of the small intestine. These enzymes continue protein digestion. They break down the more complexsubstances into amino acids. Amino acids are the final product of protein digestion.

Lipase, which is also in the gastric juices, begins the enzymatic digestion of fats. The process by which lipaseconverts fats into higher fatty acids and glycerol is limited in many species. Lipase converts fats into higher fattyacids and glycerol. This process is limited in many species. The liver secretes bile into the duodenum of the smallintestine. Bile emulsifies fats and breaks them into smaller globules. This increases the total surface area of the fats.The pancreas secretes the enzyme steapsin to complete the conversion of fats into higher fatty acids and glycerol.

The stomach of animals contains hydrochloric acid, which helps in dissolving minerals in the diet.

Absorption is the process by which digested nutrients pass from the walls of the digestive tract into the blood. Incarnivores and omnivores, most absorption occurs in the small intestine. Some absorption occurs in the smallintestine of herbivores. No absorption occurs in the mouth or esophagus. Very little absorption occurs in thestomachs of non-ruminants. The large intestine absorbs very few nutrients, except for water in carnivores. This isconverse to herbivores in which the large intestine in the site of substantial absorption.

The small intestine is lined with a large number of small, finger-like projections (villi). These villi absorb foodnutrients. They contain many blood vessels responsible for collecting and absorbing nutrients.

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Fatty acids and glycerol are the end products of fat digestion. The lymph absorbs these products. The final productsof carbohydrate digestion are monosaccharides and VFAs (volatile fatty acids). The end products of protein digestionare amino acids and peptides. They are all absorbed by the blood. Water and inorganic salts are also absorbed by theblood. Digestion is complete after absorption has made the nutrients available for other parts to use.

In poultry, the gizzard secretes no enzymes; it only functions in grinding coarse food. Feed passes from the gizzardinto the duodenum, which is parallel to the pancreas in other species. This is where pancreatic juices are broughtinto the mix. The juices contain amylolytic, lipolytic, and proteolytic enzymes. Liver bile is also secreted into theduodenum to aid in the digestion of fats. The enzyme erepsin finishes digesting proteins for conversion into aminoacids. This happens in the small intestine. Some sugar-splitting enzymes further simplify starches. The villi of thesmall intestine are the primary site of absorption.

SUMMARY

The digestive system is the gateway for nutrients from the outside environment to get to the circulatory system to bemoved to other body parts. It is a tube that runs from the mouth to the anus. As food goes through this tube, it isdisassembled by the parts of the digestive tract. Its goal is to change food nutrients into compounds that are easilyabsorbed. The circulatory system then takes these compounds to the other parts of the body. These nutrients areused for energy, growth, and maintenance of body wastes. The functions of the digestive system include ingestingfood, grinding food, digesting food, absorbing nutrients, and eliminating solid wastes.

Acknowledgements

Kristy Corley, Graduate Technician, Department of Agricultural Education,Texas A&M University, revised this topic.

Larry Ermis, Curriculum Specialist, Instructional Materials Service,Texas A&M University, reviewed this topic.

Vickie Marriott, Office Software Associate, Instructional Materials Service,Texas A&M University, prepared the layout and design for this topic.

Christine Stetter, Artist, Instructional Materials Service,Texas A&M University, prepared the illustrations for this topic.

REFERENCES

Campbell, John R. and John F. Lasley. The Science of Animals That Serve Humanity. St. Louis, MO:McGraw Hill Book Company, 2001.

Digestive System. [On-line]. Available: http://encarta.msn.com/find/search.asp?search=digestion. [2002, March].

Frandson, R. D. Anatomy and Physiology of Animals. Philadelphia, PA: Lea & Fibiger, 1992.

Pathophysiology of Digestion. [On-line]. Available: http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/index.html. [2002, March].

Stufflebeam, Charles E. Principles of Animal Agriculture. Englewood Cliffs, NJ: Prentice Hall, Inc., 1983.

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GLOSSARY OF TERMS

Abdomen – Part of the body that lies between the thorax and the pelvis and encloses the stomach, intestines,liver, spleen, and pancreas; the belly.

Absorption – Process of absorbing or being absorbed.

Accessory glands – A supplementary gland that assists in digesting food.

Bile – Bitter, greenish fluid secreted by the liver and stored in the gallbladder to aid digestion.

Bolus – Regurgitated food that has been chewed again and is ready to be swallowed.

Capacity – The maximum amount that can be contained.

Carbohydrates – Foods consisting of carbon, hydrogen, and oxygen, such as starch, sugar, and cellulose thatare a large part of animal food.

Cellulose – Main carbohydrate part of plant cell membranes digested by microorganisms.

Converse – Reversed order of relation.

Defecation – The elimination of fecal material (solid body waste) from the rectum.

Deglutition – The act of swallowing.

Disseminates – Spreads; distributes; disperses.

Dorsal – Pertaining to the back of an animal.

Emulsifies – Process of suspending in a liquid form.

Endocrine – Pertaining to glands that secrete hormones directly into the blood or lymph system.

Enzyme – A complex protein produced in living cells that promotes changes in other substances without beingused up in the process.

Epithelium – Cellular tissue that covers surfaces, forms glands, and lines body cavities of animals.

Expulsion – Ejection; dismissal.

Fecal – Pertaining to solid waste passed out of the body through the rectum.

Gastric – Pertaining to the stomach.

Glandular – Of or relating to a gland and its secretions.

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Hepatic – Related to the liver.

Ingesting – Taking in food for digestion through the mouth; eating.

Inorganic – Pertaining to substances not produced by plant or animal organisms.

Mammals – Animals that produce milk to suckle their young.

Mandibular – Pertaining to the jaw of an animal.

Mastication – The chewing of food.

Microorganisms – Microscopic bacteria or protozoa aiding food digestion, especially in ruminants.

Motility – Process of contracting or shrinking.

Proteins – Substances composed of amino acids used in the development of most body tissues.

Regurgitation – Casting up of undigested food from the stomach to the mouth for chewing again, as by ruminants.

Remastication – Chewing again of foods brought to the mouth from the stomach by regurgitation.

Ventral – Denoting a position toward the abdomen or belly of animals.

SELECTED STUDENT ACTIVITIES

1. List the five functions of the digestive system.a. _________________________________________________________________________

b. _________________________________________________________________________

c. _________________________________________________________________________

d. _________________________________________________________________________

e. _________________________________________________________________________

2. Define and provide two examples of animal species for each term listed.Herbivores - ___________________________________________________________________

____________________________________________________________________________

Omnivores - ___________________________________________________________________

____________________________________________________________________________

Carnivores - ___________________________________________________________________

____________________________________________________________________________

Ruminants - ___________________________________________________________________

____________________________________________________________________________

Non-ruminants - ________________________________________________________________

____________________________________________________________________________

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3. List the six major parts of the digestive system and describe their primary functions.a. _________________________________________________________________________

b. _________________________________________________________________________

c. _________________________________________________________________________

d. _________________________________________________________________________

e. _________________________________________________________________________

f. _________________________________________________________________________

4. Name three accessory glands of the digestive system and describe their functions.a. _________________________________________________________________________

b. _________________________________________________________________________

c. _________________________________________________________________________

5. Name the four parts of the ruminant stomach.a. _________________________________ c. __________________________________

b. _________________________________ d. __________________________________

6. Basically, how does the digestive system of ruminants differ from the digestive system of non-ruminants?____________________________________________________________________________

____________________________________________________________________________

7. How are the digestive systems of rabbits and horses (non-ruminants) able to use roughages in their diets?____________________________________________________________________________

____________________________________________________________________________

8. How does the digestive system of poultry differ from the digestive system of other domestic animals?____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

9. List three general processes (actions) of the digestive system. Provide two examples for each.a. _________________________________________________________________________

b. _________________________________________________________________________

c. _________________________________________________________________________

10. What controls the appetite of animals?____________________________________________________________________________

____________________________________________________________________________

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11. Define rumination.____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

12. Where and how is carbohydrate digestion accomplished?____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

13. Where and how is protein digestion accomplished?____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

14. Where and how is fat digestion accomplished?____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

15. Where is absorption accomplished?____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

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ADVANCED ACTIVITIES

1. Research the digestive system in other available information resources for an animal species (for example,search the Internet for “digestive system AND horse”). Then, in your own words, explain the digestivesystem’s function for the animal species. Explain the relationship between the digestive system and otherbody organ systems of the animal species.

2. Draw a detailed illustration of the digestive tract of an animal of your choice. Label all the appropriateparts.

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ALL RIGHTS RESERVED

Reproduction prohibited without written permission.Instructional Materials Service

Texas A&M University2588 TAMUS

College Station, Texas 77843-2588http://www-ims.tamu.edu

2002