Which of the following glandular secretionsinvolved in digestion would be most likelyto be released initially as inactiveprecursors?– A. carbohydrate-digesting enzymes– B. fat-solubilizing bile salts– C. acid-neutralizing bicarbonate– D. protein-digesting enzymes– E. hormones such as gastrinLE 41-22PancreasStomachEntero-gastroneGall-bladderLiverDuodenumSecretinCCKCCKStimulationInhibitionGastrinKeyAbsorption of Nutrients• The small intestine has a huge surfacearea, due to villi and microvilli that areexposed to the intestinal lumen• The enormous microvillar surfacegreatly increases the rate of nutrientabsorptionLE 41-23KeyNutrientabsorptionMicrovilli(brush border)Epithelial cellsLactealLymphvesselVilliLargecircularfoldsEpithelialcellsBloodcapillariesVein carrying bloodto hepatic portalvesselMuscle layersVilliIntestinal wall• Each villus contains a network of blood vessels and asmall lymphatic vessel called a lacteal• Amino acids and sugars pass through the epithelium of thesmall intestine and enter the bloodstream• After glycerol and fatty acids are absorbed by epithelialcells, they are recombined into fats within these cells• These fats are mixed with cholesterol and coated withprotein, forming molecules called chylomicrons, which aretransported into lactealsLE 41-24Fat dropletscoated withbile saltsFat globuleBile saltsMicelles madeup of fatty acids,monoglycerides,and bile saltsEpitheliumof smallintestineEpitheliumof lactealLactealThe Large Intestine• The large intestine, or colon, is connected tothe small intestine• Its major function is to recover water thathas entered the alimentary canal• Wastes of the digestive tract, the feces,become more solid as they move throughthe colon• Feces pass through the rectum and exit viathe anus• The colon houses strains of the bacteriumEscherichia coli, some of which produce vitaminsAfter a meal of greasy french fries, whichenzymes would you expect to be mostactive?– A. lipase, lactase, maltase– B. salivary and pancreatic amylase,disaccharidases, lipase– C. pepsin, trypsin, chymotrypsin, dipeptidases– D. gastric juice, bile, bicarbonate– E. sucrase, lipase, bileConcept 41.5: Evolutionaryadaptations of vertebrate digestivesystems are often associated withdiet• Digestive systems of vertebrates arevariations on a common plan• However, there are intriguingadaptations, often related to dietSome Dental Adaptations• Dentition, an animal’s assortment of teeth, is oneexample of structural variation reflecting diet• Mammals have specialized dentition that bestenables them to ingest their usual dietLE 41-26IncisorsCarnivoreCaninesPremolarsMolarsHerbivoreOmnivoreStomach and IntestinalAdaptations• Herbivores generally have longer alimentary canalsthan carnivores, reflecting the longer time needed todigest vegetationLE 41-27SmallintestineStomachCecumColon(largeintestine)CarnivoreHerbivoreSmall intestineSymbiotic Adaptations• Many herbivores have fermentationchambers, where symbiotic microorganismsdigest cellulose• The most elaborate adaptations for anherbivorous diet have evolved in the animalscalled ruminantsLE 41-28Intestine RumenReticulumOmasumEsophagusAbomasumLE 41-23KeyNutrientabsorptionMicrovilli(brush border)Epithelial cellsLactealLymphvesselVilliLargecircularfoldsEpithelialcellsBloodcapillariesVein carrying bloodto hepatic portalvesselMuscle layersVilliIntestinal
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