Digestion Study Guide: Animal Science Exam #2

Digestion
Summary: To study the anatomical and functional processes of the digestive tract and the differences thereof in different species/categories of animals.

Digestion- The physical and chemical changes that feeds undergo in the gastrointestinal tract and the release of nutrients for absorption

Physical, chemical and enzymatic breakdown

Classification of Digestive Systems:

   What they eat: carnivores, omnivores, herbivores

   Functional classification: Mono-gastric vs. Ruminant

Ruminant- Hooved animals, compartmentalized stomach, complicated fermentation

Mono-gastric- Simple stomach, fermentation in cecum

Enzymes: catalysts composed of amino acids which promote change (break down food)

Absorption: passage of nutrients released in digestion through the intestinal wall to the circulatory system

Metabolism: recombination/use of nutrients to create elements helpful to the body

Ex: Fats make energy

      Amino acids recombined to make proteins

Utilizing a ration

1. Digestion
2. Absorption
3. Circulation
4. Metabolism

STEPS OF DIGESTION

1. Prehension- how an animal gathers food
1. Lips
2. Teeth
3. Tongue
2. Mastication- chewing
1. Mechanical breakdown
2. Increases surface area- More area to be surrounded by enzymes to break down feed
3. Ruminants have dental pad, no upper incisors so they have rumination and vertical/lateral jaw movement as adaptations due to this
3. Saliva secretion
1. Lubrication
2. pH buffer (b/c stomach's high acidity)
3. Anti-foaming agent
4. Salivary Amylase in pigs
4. Deglutition- swallowing
1. Involuntary (neural control)
2. Peristaltic waves- contraction and relaxation of muscles in a wave down the digestive tract which helps propel content through the digestive tract
5. Stomach/Proventriculus (avian)/ Abomasum (ruminant)
1. Physical breakdown
2. Chemical breakdown
1. HCl (hydrochloric acid)- denatures protein
2. Acidic
3. Helps enzymes work
3. Enzymatic breakdown
1. Pepsin, renin and lipase
6. From stomach to small intestine
1. Chyme-Slurry feed at this point in digestion
2. Mixed with alkaline secretions- buffer acidic pH
1. Bile- Helps digest fat
1. Formed in liver
2. Stored in gall bladder
2. Pancreatic Juice- made of enzymes
1. Trypsin, chymotrypsin, carboxy-peptidase, amino-peptidase, intestinal lipase, amylase
7. Small Intestine
1. Duodenum- bile and pancreatic secretions, main site of food breakdown
2. Jejunum- main site of absorption
1. Villi- finger-like projections which increase surface area for better absorption
2. After absorption, nutrients passes into liver then are distributed to the lymph or circulatory system
1. Capillary network
2. Portal vein to the liver
3. Absorption is an active process- requires energy
3. Ileum- small amount of absorption, end of small intestine
8. Large intestine
1. Colon
2. Cecum- works as a fermentation chamber, breaks down complex carbohydrates
1. Functionality varies by species
2. Mono-gastric herbivores- high functionality
1. Allows for lower quality feeds
2. Absorbs less nutrients because at the end of the digestive system, not much space to absorb nutrients
1. Cecotrophy- consumption of excretion with nutrients from the cecum; have high protein and nutrients
3. Rectum- excretion
1. Defecation
1. Quantity related to how much is digested
2. Feces:
1. 50% bacteria by weight
2. Sloughed cells
3. Undigested feed
4. Breakdown products of digestion
2. Micturition- urination
1. Water and nitrogen compound
1. Urea in mammals
2. Uric acid in birds
3. Nitrogen from protein

EXAMPLES OF DIFFERENT SPECIES

1. Pig (Monogastric Omnivore)

Salivary amylase (only farm animal) Begins to break down starch Little nutritional importance pH in stomach is too acidic for amlyase Digestion #1 Large dependence on enzymes Enzymes typical of monogastric animal Digestion of protein is completed in intestine Duodenum Pancreatic Juice Enzymes that aid in digestion Sodium carbonate and bicarbonate Neutralize acid from stomach Pancreas produces insulin Bile Digestion and absorption of fats Absorption of fat-soluble vitamins

2. Ruminant (ex: Cattle, Sheep)

1. Can use roughages (cellulose) as source of energy
2. Mastication
1. No upper incisors, only a thick dental pad
3. Fermentation
1. Microbial populations breakdown/digest feeds (complex carbohydrates)
2. End products
1. Bacteria secretions and excretions, gases, bodies of bacteria (protein)Nutrients: VFAs,
3. Preferred diets of bacteria
1. EXTREME specialization
2. Digest specific carbohydrates, proteins, amino acids
3. Many species of bacteria present
4. LESS EFFICIENT because bacteria acts as a middleman
5. Protein broken down into ammonia and organic acids
1. Ammonia is used to produce amino acids
6. Large levels of fat are bad for microbes and thus ruminants
7. Gas and heat produced which can help warm animal

Viii.    Volatile Fatty Acids (VFAs)

1. Produced by microorganisms during fermentation
2. Absorbed and used as an energy source
3. Primary energy source in ruminants and non-ruminant herbivores
4. Ex: acetate, propionate, butyrate, etc.

4. Rumination
1. Fills the rumen rapidly with little to no time to chew
2. Rumination- regurgitation and re-chewing of feed to increase surface area
3. More fiber in diet=more rumination
5. Four parts of compartmentalized stomach (the rumen)
1. Rumen (Paunch)
1. Site of huge amount of anaerobic fermentation
1. VFA and Protein Production
1. VFAs absorbed through rumen wall
2. Protein IS the bacteria
2. Gas production
1. Eructation (belching)
2. Uses energy
3. Possibility of LETHAL BLOAT
2. Where food is stored until animal can chew it
1. Larger pieces float to the top to be regurgitated and re-chewed
3. Bacteria digests complex carbohydrates (cellulose and starches) and other plant materials
2. Reticulum (Honeycomb)
1. Fermentation
2. Pacemaker for rumen contractions
1. Mixes feed so that it doesn't block off digestive tract
3. Mixes food
3. Omasum (many plies)
1. Large folds (plies) in lining- provides extra capacity, keeps large particles from getting though
2. Probably absorbs water, electrolytes, VFAs
3. Reduces particle size
4. Abomasum (true stomach)
1. Lined with mucous membranes
2. Gastric juices are secreted
5. From abomasum to anus, Ruminant is same as monogastric
6. Benefits of microbial fermentation
1. Microorganisms make protein
1. Convert NPN (non-protein nitrogen) such as urea into bacterial protein
2. Bacteria passes down tract with feed
1. Digested in abomasum and small intestine
2. Extra protein
3. Bacteria contain energy, vitamin K, and water-soluble vitamins
4. Produce essential fatty acids
5. Microorganisms and ruminant live in symbiosis
1. Animal benefits: feed digestion, extra nutrients
2. Bacteria benefits: ideal environment
6. Poor quality feeds can be digested
7. Negatives of fermentation
1. Eructation
1. Important mechanism for ruminants
2. Large quantities of gas produced by microorganisms
3. Belched out of the rumen- enters lungs and is breathed out (muffles the sound)
4. Potential for bloating
2. Wasted energy/added middle man

Avian

1. Similar to other monogastrics
1. Lack of teeth
2. Presence of gizzard and crop
2. Crop
1. Dilation of the esophagus
2. SMALL amount of fermentation in some species
3. Food storing and moistening
3. Proventriculus (true stomach)
1. Gastric juice production
1. HCl
2. Pepsin
2. Fast rate of passage: Feed passes through in a matter of seconds, almost no digestion takes place
4. Gizzard
1. Grinding organ (physical breakdown)
2. No enzymes secreted, but enzymes from proventriculus work here
5. Small Intestine
1. No specifically separated jejunum or ileum
6. Large Intestine
1. Two ceca (functionality varies)
2. Short
3. Not divided into distinct rectum or colon
4. Vitamin K manufactured
7. Cloaca
1. Common orifice for waste elimination, copulation, and egg laying
1. Uric Acid

Horse (Non-Ruminant Herbivore)

1. Capable of using roughage
2. Adult animal only needs maintenance; able to absorb VFAs from walls of cecum to get energy benefit
3. 2/3 as efficient as a ruminant
4. Active cecal bacteria population
5. Prehension
1. Flexible upper lip, teeth, and tongue
6. Saliva contains no enzymes, but an important lubricant
1. Large amount
7. Mastication
1. Upper and lower incisors
2. Vertical and lateral jaw movement
8. Deglutition
1. One-way peristalsis
1. No rumination
2. No regurgitation
9. Stomach
1. Small capacity
1. Continuous eating
2. Low muscular activity
3. Very susceptible to stomach disorders
1. Colic, ruptured stomach
10. Small intestine
1. No gallbladder
2. Absorption
11. Large intestine (Over 60% of gut capacity)
1. LARGE cecum
1. VFAs absorbed through cecum walls
2. Large colon
3. Small colon
4. Rectum
12. Coprophagy (consumption of cecal excrement) occurs in horses on a poor diet

ORDER IN MONOGASTRIC

1. Prehension
2. Mastication
3. Deglutition
4. Stomach/Proventriculus
5. Small Intestine
1. Duodenum
2. Jejunum
3. Ileum
6. Large intestine
1. Colon
2. Cecum
3. Rectum

ORDER IN RUMINANT

1. Prehension
2. Mastication
3. Deglutition
4. Rumen
1. Rumination
5. Reticulum
6. Omasum
7. Abomasum (true stomach)
8. Small Intestine
1. Duodenum
2. Jejunum
3. Ileum
9. Large Intestine
1. Colon
2. Cecum
3. Rectum

ORDER IN AVIAN

1. Prehension
2. Deglutination
3. Crop
4. Proventriculus (stomach)
5. Gizzard
6. Small Intestine
7. Large Intestine
1. Two ceca
8. Cloaca

ORDER IN MONOGASTRIC HERBIVORE

1. Prehension
2. Mastication
3. Deglutination
4. Stomach
5. Small Intestine
1. Duodenum
2. Jejunum
3. Ileum
6. Large Intestine
1. Cecum
2. Large colon
3. Small colon
4. Rectum