What organs are apart of the digestive tract? What organs are associated?
- Mouth - mechanical chewing
- Esophagus - tube that guides food into stomach
- Stomach - biggest difference in species is single or multiple
- Small intestine - main site for nutrient absorption
- Large intestine
- Caecum - pouch, blind sac
- Associated: liver, pancreas, gall bladder
What are the four systems? Which is the human system?
- 1. Simple system (without functional caecum)
- 2. Simple system (with functional caecum)
- 3. Ruminant system
- 4. Avian system
- The simple system with no functional caecum
What are the main points about the simple system without functional caecum?
- Suited for a nutrient dense, low fibre diet - compared to other species we need less fibre
What is the role of the oral cavity in digestion?
- Initation of digestion
- Chewing, saliva, secretion of enzymes
What is the role of the stomach in digestion?
- Mechanical role
- gastric secretions (HCl)
- Exapandable reservoir
- Food is mechanically disrupted, churned and ground to a liquid mass called chyme
- Initiation of protein digestion
What is the role of the small intestine in digestion?
- Key site for nutrient digestion and absorption
- Acidity neutralized by pancreatic secretions
- Change in pH environment - bicarbonate is secreted and acid is neutralized
- Secretion of bile acids synthesized in the liver, stored in the gall bladder and released to aid in lipid digestion
What is the role of the large intestine in digestion?
- Unabsorbed food materials, water and salt absorption
- Little secretion and digestion
- Bacterial fermentation and some vitamin synthesis - baceria ferment unabsorbed food and synthesize various vitamins which contributes to the diet requirement
- Water of chyme reabsorbed into the body therefore, chyme becomes more solid
Describe the structure of the small intestine. What are the 3 folds and how does this help?
- Massive folding increases surface area for optimal rate of nturient absorption
- 1. Submucosal folds: large folds under mucosa, protude into lumen
- 2. Villi: mucosa folds into villi, finger like projections into lumen
- 3. Microvilli: hairlike projections on each cell of every villus
- Microvilli comprise the brush border membrane - critical for nutrient absorption into the blood stream
What are the 3 forms of nutrient transport?
- 1. Diffusion - goes straight through BBM
- 2. Facilitated diffusion - transporter helps with movement through BBM
- 3. Active transport - uses ATP and transporter
How much bacteria is in the LI and what is the major type?
What materials do they breakdown? How much energy does this provide?
- 1012/g bacteria
- Mostly anaerobic bacteria
- Bacterial ermentation of undigested carbs, proteins, alcohols, fibres etc. - break down what human enzymes cannot, used for their own energy and some biproducts become beneficial to the human
- Carb fermentation (fibres) generate lactate and short chain FA or VFA - mainly 2C acetate, 3C proprionate and 4C butyrate
- FA are then absorbed by LI and into blood stream
- Provides 5-10% of energy needs
- **Only in LI does bacteria fermentation occur in systems without a functional caecum**
What are the main properties of a simple system with a functional caecum?
- ex: horse, rabbit, hamster
- Pseudoruminant - hindgut fermenter (refers to functional caecum to ferment fibre)
- Functional caecum
- Suited for diet with large amounts of forage - high fibre
What is the benefit of a caecum? What is coprophagy?
- Rich in microbial population, bacterial fermentation of cellulose, hemicellulose etc.
- Production of volatile FA - source of energy and get absorbed by caecum into blood stream (some fermentation occurs in LI)
- Occurs in 2 places therefore more synthesis of VFA and more energy
Coprophagy: ingestion of feces to obtain nutrient value
What are the main properties of the ruminant system?
- It is a multiple system in the is has multiple stomach compartments
- Ex: cattle, sheep, goats
- Large stomach divided into 4 sections: rumen, reticulum, omasum, abomasum
- System highly suited for animals that eat a very high quantity of roughage - high fibre
What do the rumen and reticulum comprise? What is the main function?
- Make up the large fermentation vat
- Ruman has 10-50 billion bacteria/g of ruminal fluid and has papillae
- Fermentation takes place before entering the intestine (foregut fermenter)
- Butrient produced are avaialble for subsequent digestion and absorption
- VFAs can be absorbed through the rumen wall or will continue in digestion
- VFAs are a significant energy source - 60 -80% or energy needs
- Large particles can be regurgitated, taken back up through esophagus and can be mechanically broken down
What is the function of the omasum?
- Removes excess water
- Water and salts absorbed
- Also absorbs VFAs not absorbed through the rumen wall
What is the function of the abomasum?
- Most similar to human stomach
- Initiation of protein digestion
- Secretes HCl
In the ruminant system, what is the function of the small intestine, the caecum and the large intestine?
- Similar to other species although a lot of nutreitn absorption has already happened
- Further fermentation and water absorption - any undigested material
What are the advantages to the ruminant system?
- Vitamin B and K synthesis - biproduct from bacteria
- Non-protein nitrogen utlization - bacteria synthesize protein from low quality protein and non protein nitrogen and this microbial protein is then degraded providing essential a.a. to the animal
- VFA production - energy and precursors for synthesis of other molecules
What are the disadvantages of the ruminant system?
- carbs (starches and sugars) are inefficiently used
- fermentation creates heat
What are the main properties of the avian system?
- Ex: chicken, turkeys
- Beaks and claws are important for breaking up foods into smaller pieces the birds can swallow
- rapid digestion because birds have to maintain low body weight to fly
What is the crop in the avian system?
- Storage sac
- Mucous softens food by secretions
- Allows birds to pick up food its going to eat and fly away
What are the components of the two chamber stomach of the avian system?
- Provetriculis: glandular stomach, secretes HCl - similar to human stomach
- Gizzard: (ventriculus) muscular organ, grinds tough food - mchanical disruption of food - stones and grit that may be picked up can help break apart
Function of the small intestine in the avian system?
- Similar function to other species - main site for absorption
- Very short, food moves up and down to increase surface area and increase nutrient absorption
Function of the caecum in the avian system?
- There are usually 2
- Minor site of bacterial fermentation
- Food moves quickly therefore not much time for bacterial fermentation
Function of the large intestine in the avian system?
- very short
- water and salt absorption
- little digestion
Function of the cloaca in the avian system?
Combined output of kidneys (uric acid) and large intestin (feces), rapid voiding
What is digestibility? How is it calculated and what does it represent?
- A measure of the fraction of a specific nutrient or of energy that is extracted by the gastrointestinal tract
- calculated from the amount of nturient in the diet and amount appearing in the feces
- Represents a combination of nutrient release from the food matric, microbial fermentation and absorption
- How good the body is at extracting the nutrients as it goes through digestion
What is the total collection method? How is it done?
- Simplest measure of digestibility
- Allow the animal to adapt to a diet over a 7-21 day period
- Isolate animals for quantitative analysis
- Measure itnake over 3-10 day period
- Collect and weigh all feces
- Analyze for nutrient interest in both diet and feces
What is the apparent digestibility coefficient and how is it calculated with the totell collection method?
- Indication of how digestible a nutrient is - if it is high it is very digestible = very good
- ADC = total intake - total feces/ total intake
What are the limitations to the total collection method?
- Accuracy in measuring food intake
- Metabolic cages = anxious animals
- Labour intensive
- Animals confined in costly equipment
- Not ideal for captive wild animals
What is the indicator method? What does it require?
- Measures digestibility by adding something to the diet
- Requires a marker: internal (natural component in the feed such as indigestible fibre) or external (component added to the feed)
What are the characterisitcs of a marker for indicator method?
- Non-absorbale, not altered by GI tract in any way
- Mixes easily with food
- easily and accurately measured in sample
- Ex: ferric oxide, chromic oxide, silica, lignin
How is the indicator method done? How does it calculate the ADC?
- 1. Adapt the animal to the test diet - includes marker
- 2. Collect a feed and fecal sample
- 3. Analyze each for marker and nutrient of interest
- ADC = Ratio of nutrient/marker in feed - ratio of nutrient/marker in feces // ratio of nutrient/marker in feed
- In diet, marker is in small ratio to nutrient and in feces, at high ratio
What are the advantages to the indicator method?
- Total weight of feed and feces not required
- Much less labour intensive
- *Most macronutrients has high digestibility
Why is apparent digestibility an underestimation of true digestibility?
- Endogenous secretion might occur in the digestive tract - epithelial cells release FA due to rapid trunover rate
- Bacterial growth in gut - nutrient synthesis of biotin
- Both are measuring nutrients that werent in the diet
- Digestive enzymes - protein secretion
How do you determine true digestibility?
- 1. Perform digestibility study using TEST DIET
- 2. Switch to diet containing none of the nutrient of interest (ZERO NUTRIENT DIET)
- 3. Analyze feces after previous diet is cleared
- 4. Subtract level of nutrient in feces of animals fed the NUTRIENT ZERO from the TEST
How is the true digestibility coefficient calculated?
- TDC = A - (B-C) / A
- A = ratio of nutrient/marker in feed
- B = ratio of nutrient/marker in feces
- C = ratio of nutrient/ marker in feces after zero nutrient diet