DIGESTION

Procedures

• YELLOW words are vocabulary terms and should be recorded
• STOP signs photos mean there is some type of activity or review
• GREEN items are review

or additional activities we will do

​

Rate your knowledge …

Digestive Expert – Green

Digestive Novice – Yellow

• I’ve Digested Something Before - Red

• Suck on (do not chew) a saltine
• Note what is changing and hypothesize why…..

​

WRITE OUT what just occurred/will occur to DIGEST the cracker..

​

(on scrap paper) - we will do this again in your final project.

​

Digestive Systems

• Functions of the digestive system include:
• eating (ingestion)
• chewing (mastication)
• swallowing (deglutition)
• absorption of nutrients
• elimination of solid wastes (defecation)

​

Revise your description using these terms

Digestive System

• FUNCTION (simplified)
• Convert, use and transport nutrients
• AKA GI Tract
• Gastrointestinal tract
• Herbivores, carnivores and omnivores vary what they eat and how they digest
• List examples of each

What are the THREE

types of GI tracts?

​

1. Ruminant Digestive Systems

• Ruminants are those animals that contain a multi-chambered digestive system (polygastric) that allows the animal to gain the majority of their nutritional needs from forages and other roughages.
• Forage refer to grasses
• Roughages refer to high-fiber food.
• Regurgitate food and chew it – CUD
• No upper front teeth – dental pad

2. Monogastic Digestive Systems

• Simple are those animals that contain a one-chambered digestive system (stomach) (monogastric)

3. Avian Digestive Systems

• Avian (birds) have a modified simple digestive system

(we will discuss more later)

List example species of each

What was different about the digestive system of the horse?

​

• The horse and rabbit have an enlargement know as a cecum that enables the animal to utilize high fiber feeds by means of microbial fermentation.
• Called Pseduo-ruminents

Digestive System Length

• The digestive tract extends from the lips to the anus. It includes the mouth, pharynx, esophagus, stomach, and the small and large intestines.
• Accessory glands include the salivary glands, the liver, and the pancreas.

Let’s Practice –

Human Digestive System MODEL

(grab a notecard – be ready to do as it says and read the function)

​

• Mouth – grasps the food
• Teeth- provide mechanical digestion of feed by breaking, cutting, and tearing up food.
• The increase surface area aids in the chewing and swallowing process.

​

​

3. Tongue - covered with finger-like projections (papillae), contain taste buds.

​

4. Salivary glands - secrete saliva, that moistens food and is mixed with the food material to aid in swallowing.

• Saliva contains enzymes – speed up chemical reactions (digestion)

​

Water: moistens consumed feed and aids in the taste mechanisms.

Mucin: lubrication aid for swallowing.

Bicarbonate Salts: acts as a buffer to regulate pH of the stomach.

Enzyme: salivary amylase initiates carbohydrate breakdown.

​

Mature horses can produce 10 gal/day; cows- 12 gal/day; and sheep- 2 gal/day.

​

What happens in the mouth?

Rate your knowledge …

Digestive Expert – Green

Digestive Novice – Yellow

I’ve Digested Something Before - Red

• 5. Pharynx - funnels food into the esophagus, preventing food material from entering the lungs.

​

• 6. Esophagus hollow muscular tube from the mouth to the stomach; material is moved by a series of muscular contractions referred to as peristatic waves.
• Also serves as a storage for food (crop) in chickens.

• 7. Cardiac Sphincter: valve at the junction of the stomach & esophagus

​

• 8. Simple Stomach:
• Storage of ingested feed.
• Muscular movements (physical breakdown)
• Secretes digestive juices:
• 1) Hydrochloric Acid
• 2) Pepsin
• 3) Rennin
• Material leaving the stomach is called chyme.

​

Let’s Review:

With a partner, digest the snack

in front of you and describe

what is happening to the food

as it moves through your GI.

​

OR…

• 8. Multi-chambered “ruminant stomach”

• Divided into 4 compartments
• Rumen
• Reticulum
• Omasum
• Abomasum

Quick Rumination Video

Cud Chewing

• Regurgitation of partially-digested feed so that it can be further reduced in size to aid microbial fermentation.
• The cud, or bolus - carried to the mouth by the esophagus.
• Must also release the enormous quantities of gas that build up as a result of fermentation.
• Failure to do so can result in bloating, a� severe and potentially fatal condition �for a ruminant that can interfere with�breathing and cause suffocation.

Interpret

• Largest portion of ruminant stomach (55-65 gallons)
• Functions include:
• Storage
• Soaking
• Physical mixing and breakdown
• Rumen compartment is quite undeveloped at birth and may be functional by 6 to 8 weeks of age.

​

A. Rumen

A. Rumen (cont.)

• Balance of chemical AND physical breakdown
• Walls contain papillae (finger like projections to aid in secretion of enzymes)
• Contractions occur inside muscular walls 1-3 times per minute. This allows mixing and digestion of fermented feed.
• When sick or if rumen is too acidic, contractions slow and digestion fails

​

​

12 Week Old Calf Rumen

Why do calves drink milk while

cattle eat silage?

​

Why do piglets drink milk while

sows digest corn?

​

A. Reticulum

• Tough, honeycomb like structure, puncture resistant, lower portion of the
• ‘Catches’ foreign objects and prevents them from causing further harm downstream of the rumen.
• Once items “sink” and are “caught” they stay there forever unless removed

​

​

Reticulum – full – left

Reticulum – cleaned - lower

Reticulum – enlarged – bottom left

Telephone Cord

Wire

Sponge taken from digestive system of an animal

​

T. Left – Cow

magnet used verses

after harvest.

B. Left – New

magnet

B. Right – Insertion

Using balling gun

A. Omasum

• Section that is round and muscular
• Resembles pages of an open book
• “Grinds” the food material and prepares the food material for chemical breakdown. Absorbs water, volatile fatty acids and nutrients
• Folds trap digested particles to maximize absorption
• Injects a soupy mixture of partially digested forage and microbes into this structure

​

A. Abomasum

• It operates much like our own stomachs (but handles more bacteria than ours)
• It secretes acid and digestive enzymes
• Where the majority of chemical breakdown of food material occurs.
• Mixes in digestive enzymes (pepsin, rennin, bile, etc.).

Let’s Review:

With a partner, digest the snack

in front of you and describe

what is happening to the food

as it moves through your GI.

​

9. Small Intestine - where most of the food material is absorbed into the bloodstream

• Contains three sections:
• duodenum
• jejunum
• ileum

A. Duodenum: first section (active digestion)

-Receives secretions from:

Pancreas: acts on proteins, carbohydrates and lipids

Liver: bile (stored in the gallbladder) breaks down fat. *Horses do not have gallbladders

B. Jejunum: middle section; active in nutrient absorption

C. Ileum: last section; active in nutrient absorption

Small Intestines

• Walls of the S.I. are lined with a series of fingerlike projections called villi, which in turn have minute projections called microvilli that increase the nutrient absorption area.

• 10. Large Intestines
• Site of water restoration
• Secretion of some mineral elements
• Storage reservoir calcium
• of undigested GIT contents.
• Bacterial fermentation:
• Synthesis of some water-soluble vitamins and vitamin K.
• Some bacterial breakdown of fibrous ingredients.
• Synthesis of some protein,

A. Cecum:

• first section
• size varies considerably in different species;
• No significance in the pig or human (dead end)
• IMPORTANT in horse and rabbit
• Bacterial breakdown of cellulose and other carbohydrate material to produce VFAs thus, the horse can utilize fibrous feeds.
• Site of bacterial synthesis of water-soluble vitamins and protein.

• B. Colon:
• middle section
• largest part of the L.I.
• Primary area of water restoration from intestinal contents.
• C. Rectum: last section of the L.I. and the end of the digestive tract before the unabsorbed material (feces) is excreted out the anus (preparation for excretion) (poop chute)

​

​

​

​

11. Anus - opening through which the waste is removed.

Controlled by sphincter muscles, that also help protect the opening.

Let’s Review:

Go to a review station and put

terms of the digestive tract

in order using only each other

as resources (no notes – TALK it

through!)

​

Avian Digestive System

Hypothesize:

Why are tukeys found so

commonly on the side

of the road?

​

The avian digestive system is the type found in poultry.

This system differs greatly!

• Since a bird has no teeth, no chewing
• The esophagus empties directly into the crop.
• Crop = where the food is stored and soaked.
• Proventriculus = glandular stomach (HCI and gastric juices); enzymatic (like a human stomach)
• Gizzard = very muscular organ, which normally contains stones or grit that grinds the food.
• Cloaca = posterior opening (similar to anus) – one opening for urinary, intestinal and reproductive tract

​

Hypothesize:

Will digestion be fastest in a

monogastric, polygastric

or avian GI? Why?

​

Questions?

Just for Fun…

Which mammal has the longest digestive system?

​

Guesses???

Koala

​

Largest Herbivore

​

Just for Fun…

How long does digestion take…

​

Guesses???

IT DEPENDS…�

• What was eating
• What animal is digesting
• If digestive tract/bacteria are working correctly

​

(Average 3-6 hours)

Ferrets = FASTEST (30 min)

Sloths

Everything about a sloth is slow-moving, including his digestive system. It can take up to a month

Just for Fun…

How many stomachs

does a whale have?

​

Guesses???

Whales have a three-sectioned stomach. The first section of a whale's stomach breaks down its food by crushing. The second section mixes the food with digestive juices and the third further mixes the food and digestive juices.

Rate your knowledge …

Digestive Expert – Green

Digestive Novice – Yellow

I’ve Digested Something Before - Red

Additional Resources

Video Link to Fistula Cow

​

Video Link to 3D Horse Digestion Guide

​

CrashCourse Video – Digestion

​

Cat Dissection Video – Digestive Tract

​

Questions?