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1、Comparative Digestive PhysiologyWhy Do Animals Digest?Food not ingested in suitable statePhysical nature of food determined by:gathering apparatus for uptaketype of digestive system Primary Functions of the Digestive Tract nTransport food peristaltic contractionsnDigestionnMechanical breakdownnChemi
2、cal breakdownnAbsorptionnPassive diffusion and active transportnSynthesis - true protein, FA, starch, vitaminsnExcretion elimination of waste productsnVia bile (toxins, microbes etc)nVia rectum (Ca, Mg, P)Regions of Alimentary CanalnForegut functionsnIngestion and storage of feedsnMidgut functionsnM
3、echanical, chemical & enzymatic digestion of feednNutrient absorption nHindgut functionsnWater & ion re-absorptionnFormation, storage, excretion of fecesPrimitive Gastrointestinal TractnFound in monotremes (egg-laying mammals), insectivores (bats, shrews, moles), and dermopterans (colugos)nSimple st
4、omach, little or no division between small intestines and large intestines, large intestine simple, presence of cecum, non-sacculated colonSpecies-Dependent Nutritional AdaptationsnIncludes involvement of:nTeethnJaws and jaw musculaturenAlimentary canal nStomach - May be simple or become sacculated
5、to compartmentalize functions for prolonged storage of feed and utilization of bacterial fermentation (langures and ruminants)nMay also become voluminous for storage of large amounts of feed (vampire bats)nLarge intestine - varies substantially in length, compartmentalization, and complexity among s
6、peciesMouthnFunctionsnGrasp foodnTastenMasticate foodnMix with salivaDigestion in the MouthnPrehensionnBringing the food to the mouthnUpper limbs, head, beak, claws, mouth, teeth and lipsnMastication or chewingnTo crush the food, increase surface area and allow enzymes to act on moleculesnCarnivores
7、 only to reduce the size of the particle to a size small enough to swallownHerbivores must chew continuously (40- 50,000 times a day) to increase surface area PrehensionnSeizing and conveying feed to mouthnMechanisms vary with behavior and dietnForelimbs nPrimates, raccoonnSnoutnElephant, tapirnTong
8、uenAnteater, cow, sheepnLipsnHorse, sheep, rhinocerosPrehensionnDomestic mammals use lips, teeth and tonguenRelative importance varies by speciesnHorses nlips when eating from mangernteeth when grazingnCows and sheep have limited use of lipsnUse long rough tongue to grasp foragenPigs use snout to ro
9、ot in ground and pointed lower lip to convey feed into mouthnBirds use beak and tonguenDrinking varies as wellnMost mammals use suctionnDogs and cats use tongue to form ladleThe Importance of Prehension in Diet FormulationnWhite Rhino (“wijd” = wide)nSquared off upper lip used to “crop” grassnGrazes
10、 on savannahnBlack RhinonPrehensile upper lip for browsing nConsumes bushes and shrubs in forestMasticationnPhysical reduction of feednEspecially important in non-ruminant herbivoresnAdaptations with teethnCarnivoresnHerbivoresnEdentates (sloths, armadilloes, anteater)nRelative toothlessnessMorpholo
11、gical Adaptations for HerbivoryAll related to finding, ingesting, masticating, and digesting plant cell wallsDental adaptations for herbivory include changes to incisors, molar occlusal surfaces, & masseter Solution for digestive problems is to provide a place in digestive tract for anaerobic bacter
12、ia & protozoans (microflora) to colonizeTeeth SpecializationsnCarnivoresnCanine teeth highly developed and used for tearingnMolars are pointed for bone crushingTeeth SpecializationsnOmnivoresnGrinding teeth patterns on posterior teeth (molars)nPiercing and ripping cusps on anterior teeth (incisors)n
13、Tongue - used to move feed to teethJaw & Teeth SpecializationsnNon-ruminant herbivores (horse)nIncisors for nipping, molars slightly angled, jaws move circularly (vertical and lateral)nRuminantsnNo upper incisors, have dental pad, molars allow only lateral movementsnDifferent classes - roughage eate
14、rs, transition types, selective eaters all differ in tongue mobility and cleft palateJaw Muscles and MasticationnTemporalis muscle - develops maximum force on anterior portion of jaw (largest muscle in carnivores and smallest muscle in herbivores)nMasseter and medial pterogoid - maximum force for cr
15、ushing and grindingnLateral pterogoid - allows lateral movement which is important for grinding (highly important in herbivores, but carnivores and many omnivores have almost no lateral movement of jaws)SalivationnQuantity and composition of saliva varies considerably between speciesnQuantity relate
16、d to level of chewing activitynAmount of secretionnDogsminimal (lubrication, no enzymes)nSheep3-10 liters/dnHorse10-12 liters/dnCattle130-180 liters/dEsophagusnSpecies adaptationsnAbility to control peristaltic contractionsReverse peristalsis Amount and location of skeletal muscleRegurgitation vs. vomitingForegut in BirdsnCropnBottom of the esophagus forms a sac called crop Stores undigested food. Birds with crop gorge when fo
