Lecture 3 - Digestive Systems

Lecture 3 - Digestive Systems - THE DIGESTIVE SYSTEM...

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Unformatted text preview: THE DIGESTIVE SYSTEM Different species, different needs, different systems… 1. Simple system (w/o caecum) 2. Simple system (with functional caecum) 3. Ruminant system 4. Avian system Gastrointestinal (GI) Tract • • • • • • • Mouth Esophagus Stomach Small Intestine Large Intestine where fermentation takes place - bacteria Caecum Rectum GI Tract = Digestive Tract ≠ Digestive System GI Tract = Digestive Tract does not equal Digestive System Digestive system= GI tract + associated organs (liver, organs pancreas,(liver, gallbladder) Digestive System = GI Tract + associated pancreas, gallbladder) 1. Simple System e.g. human, pig, cat, dog Monogastric that means one step Non-functional caecum Suited for a nutrient dense, low fibre diet Human digestive tract ~ 16 feet How does digestion work? • Oral cavity - food is chewed - food is mixed with saliva - 2 enzymes released: alpha-amylase and lingual lipase - this is where food gets broken down (however very minimal) is chewed Food Food is mixed with saliva Two enzymes released: α-amylase and lingual lipase * 4 regions of the stomach from top to bottom fundus, body, • Stomach (cardia, (cardia, fundus, body, antrum) - Empty= 50mL, Filled= 1-1.5L - Gastric glands secrete=gastric juice (composed of H20, electrolytes, HCL, enzymes Empty 50mL, Filled = 1-1.5L - pH of stomach is acidic ~2 Gastric glands secrete gastric juice - Food become chyme pH of stomach is acidic ~ 2 - Gastric emptying= 2-6 hrs Food become chyme Gastric emptying = 2-6 hrs Pictures from A.D.A.M., Inc. How does digestion work? Cont. (Duodenum, jejunum, ileum) *3 regions from top to bottom, jejunum is the largest part • Small intestine (duodenum, jejunum, ileum) - Main Main site forsite nutrient absorptionand absorption for digestion nutrientand digestion - Surface area= 3000m2 Surface area = 300m2 - Intestinal motility (longitudinal and circular) Intestinal motilityby(longitudinal and circular) - Chyme acidity neutralized pancreatic juice Chyme acidity neutralized byacids pancreatic juice - Digestion of food --> pancreatic juice, bile Digestion of food pancreatic juice, bile acids ( also called the colon) • Large intestine (also called the colon) Where fermentation happens: - Production of short chain fatty acids (SCFA) Fermentation - SCFA = VFA ( volatile fatty acids) Where the absorption of water happens - Production of short chain fatty acids (SCFA) - SCFA = VFA (volatile fatty acids) Water absorption Pictures from A.D.A.M., Inc. Small Intestinal Surface Area 1. Kerckring folds 2. Villi (and Crypts) 3. Microvilli Nutrient Transport Large Intestine • 1012/g bacteria – Over 400 species identified to date – 1000:1 anaerobic to aerobic – Fermentation of undigested CHO, protein, alcohols, fibres, etc. – CHO fermentation generates lactate and SCFA Bifidobacterium lactis regularis (intestinal transit time) SOURCE: www.customprobiotics.com Nutrition News 2. Simple System w functional caecum e.g. horse, rabbit, hamster • ‘Pseudo-ruminant’ • Functional caecum • Suited for a diet with large amounts of forage • Horse digestive tract ~ 100 feet 2. Simple System w/ functional caecum • Why the functional caecum? - Enormous hindgut (20-30l capacity) with bacteria - Obtains 70% energy from SCFA - Produces B-vitamins • Enormous hindgut (20-30L capacity) with bacteria • Obtains 70% energy from SCFA • Produces B-vitamins • Energy Deficiency? • Coprophagy?? • Sign of nutrient deficiency 2. Simple System w functional caecum SOURCE: www.equisearch.com III. Multiple System: Ruminant e.g. cattle, sheep, goats • Large stomach divided into 4 sections – – – – Rumen Reticulum Omasum Abomasum • System highly suited for animals that eat a high quantity of roughages How does digestion work? • Reticulum •Honeycomb appearance in order to capture particles - Honeycomb appearance in order to capture particles •Traps - Traps foreign material ( wire, nails, ect) - region ofmaterials microbial fermentation foreign (wire, nails, etc) •Region of microbial fermentation • Rumen •The largest section of the stomach - Largest section of the stomach •Rumen papillae increases for absorption - Rumen papillae --> increase surface surface areaarea for absorption - Food is&mixed & partially broken down, and store •Food is mixed partially broken down, andtemporarily stored temporarily - Rich in bacteria (fermentation vat) •Rich in bacteria (fermentation vat) - 60-80% of energy by SCFA •60-80% of energy by SCFA papillae How does digestion work? Cont. • Omasum - Resorption of water and some electrolytes - Filters large particles •Resorption of water and some electrolytes •Filters large particles • Abomasum - the 'true stomach', similar to that monogastric animals - digestive enzymes secreted from gastric glands (HCL, mucin, pepsinogen, lipase, ect) •the ‘true stomach’, similar to that of monogastric animals •digestive enzymes secreted from gastric glands (HCl, mucin, pepsinogen, lipase, etc) III. Multiple System: Ruminant Cont. • Fermentation takes place before entering the intestine (foregut digestion) • Nutrients produced are available for subsequent digestion & absorption 1. Rumination 2. Eructation (belching) III. Multiple System: Ruminant Cont. • Rumen has 10-50 billion bacteria / g of ruminal fluid • Advantages and Disadvantages with this system – Vitamin synthesis (+ve) – Non-protein nitrogen utilization (+ve) – Carbohydrate utilization (-ve) – Heat production (-ve) IV. Avian System e.g. chicken, turkey, etc • Beaks and claws are important for breaking up foods into smaller pieces the birds can swallow • Rapid digestion IV. Avian System SOURCE: http://www.geauga4h.org/poultry/ How does digestion work? • Crop - Enlarged area of the esophagus •Enlarged area of species, the esophagus - Well developed in most but not all - Serves as a temporary storage location for food - Food is softened ( Often regurgitated to feed offspring) •Well developed in most species, but not all •Serves as a temporary storage location for food •Food is softened (often regurgitated to feed offspring) • Two-chamber stomach Glander portion = Proventriculus Glandar portion = Proventriculus --> Gastric enzymes and HCL are secreted Gastric enzymes and HCl are secreted Muscular portion - Gizzard Muscular portion Gizzard --> Grind and digest tough–foods Grind and digest tough foods How does digestion work? Cont. • Small Intestine --> Similar functionality as other systems Similar functionality as other systems • Ceca --> minor site of bacterial fermentation minor site of bacterial fermentation How does digestion work? Cont. • Large Intestine - Very short and serve predominantly to connect the small intestine andthe cloaca •Very short, and serves predominantly to connect - Storage of undigested material, water absorption small intestine and cloaca •Storage of undigested material, water absorption • Cloaca - where the digestive, urinary and reproductive system meet where the digestive, urinary and reproductive systems meet Statement about the proximate analysis (multiple choice question) - Short-chain fatty acids are only extracted from a food product during the ether extraction step. Digestibility • Measure of the fraction of a specific nutrient or of energy that is extracted by the GI tract • Calculated from the amount of nutrient in the diet and the amount appearing in the feces • Represents a combination of nutrient release from the food matrix, microbial fermentation, and absorption • Why is this important? Prevents deficiency and ensures essential nutrients are available Prevents deficiency and ensures essential nutrients are available Total Collection Method • Allow the animal to adapt to the diet over a 7-21 day period • Isolate animal for quantitative analyses • Measure intake over a 3-10 day period • Collect and weigh all feces • Analyze for nutrient of interest this is going to be an approximation Apparent Digestibility Total intake – Total Feces = Coefficient Total Intake All measurements in grams SOURCE: Khan et al, IJAB 2003 Limitations of 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 Metabolic cages -> collect and analyze urine & feces Indicator Method • Also referred to as the Marker Technique • Requires a marker: – Internal (a natural component of the feed) – External (a component added to the feed) • Characteristics of a Marker? 1- Non-absorbable 2- Must not affect or be affected by the GIT Non-absorbable 3- Must mix easily with the food 1. 3. Must mix easily with the food 2. Must not affect or be affected by the GIT 4. Easily & accurately measured in samples • E.g. ferric oxide, chromic oxide, silica, lignan Indicator Method 1. Adapt animal to test diet (includes marker) 2. Collect a feed and fecal sample 3. Analyze each for marker and nutrient of interest A–B Apparent Digestibility Coefficient = A Advantages of this method? --> Less labour intensive, ideal for wild animals Example: Calculation of Apparent Digestibility FRACTION INTAKE Dry matter (DM) EXCRETION 1000 g (100%) 100 g (100%) Protein (CP) 20% 7% Fat (EE) 25% 16% CHO (NFE) 50% 28% Fibre (CF) 4% 39% Chromic oxide (fecal marker) 1% 10% Total Collection Method Apparent Digestibility Coefficient = Total intake – Total Feces Total Intake Protein = (1000g * 20%) – (100 * 7%) = 0.965 (1000 * 20%) Protein = 96.5% Digestible FRACTION Dry matter (DM) INTAKE 1000 g (100%) EXCRETION 100 g (100%) Protein (CP) 20% 7% Fat (EE) 25% 16% CHO (NFE) 50% 28% Fibre (CF) 4% 39% Chromic oxide (fecal marker) 1% 10% 2. Indicator Method Apparent Digestibility Coefficient = A–B A A = Ratio of Nutrient/Marker in Feed; B = Ratio of Nutrient/Marker in Feces Protein = 20% 7% 1% 10% 20% 1% = 0.965 Protein = 96.5% Digestible Apparent vs. True Digestibility Underestimating true digestibility? • Endogenous secretions? • Epithelial cells fatty acids • Bacterial Growth in gut • Nutrient synthesis biotin • Digestive Enzymes • Protein secretion 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 ZERO NUTRIENT DIET from the TEST DIET True Digestibility True Digestibility Coefficient = 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 DIET 1 FRACTION DIET 2 INTAKE EXCRETION INTAKE Protein (CP) 20% 7% 0% 3% Fat (EE) 25% 16% 30% 15% CHO (NFE) 50% 28% 65% 35% Fibre (CF) 4% 39% 4% 39% Chromic oxide (fecal marker) 1% 10% 1% 8% True Digestibility Coefficient = Protein = 20% 7% 3% 1% 10% 8% 20% 1% EXCRETION A – (B – C) A = 0.984 Protein = 98.4% Digestible Factors affecting Digestibility Over 50 different factors might influence digestion efficiency • • • • • Feed intake Particle size Chemical composition Climate Age ...
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