chap 8

Antrho 161 chap 8 CREATEDATE 3/11/09 7:37 PM chapter Eight the digestive tract is composed of the mouth, tongue, teeth, esophagus, stomach and the small and large intestines functions differently for each diet the survival of any organism depends on its capacity to extract nutrients from the foods that it eats Omnivore Digestive System: Human The digestive system of humans is similar to other primates, differing only in some aspects that can be traced to the dietary pattern on which they have com to depend The oral cavity and the pharynx Oral cavity: teeth that break down food; mixed with saliva Saliva contains amylase which splits starc h into molecues of double sugar maltose (process called hydrolysis) Tongue manipulates food into bolus Epiglottis: swllowing Esophagus Dissolved macromolecules pass through the pharynx and esophagus into the stomach Esophagus is a tube from the pharynx to the stomach Bolus is moved by peristalsis The stomach: digestion Enzymatic digestion begins Saclike organ with three sets of muscles Capable of a great variety of movements Chyme Once the food is in te stomach pepsin is produced by the gastric acids to act on the proteins The small intestine: nutrient absorbtion disgestion and absorbtion completed here bile secreted from the pancreas between meals, bile is stored in the gallbladder (sac underneath the liver) monosaccharides and amino acids are absorbed The large intestine: excretion and reabsorbtion Three parts: the cecum, colon and rectum Rectum produces feces that contain unabsorbed nutrients Other unused nutrients escape by other means The gastrointestinal tract is a highly complex ecosystem whose major function is to digest food and absorb nutrients. It protects the organism thorugh the action of three lines of defense: the intestinal microflora, the intestinal mucosa, and the intestinal immune system. Digestive Strategies of Herbivores Monogastric (Hindgut) Fermentation Large colon divided into the transverse, descending and ascending colon Fermentation occurs in the large intestine Only about 45% of nutrients are absorbed in nonruminent herbivores Multigastric (foregut) fermentation (rumination) Ruminants regurgitate and masticate their food after swallowing Digestive tract is composed of the mouth , tounge, teeth, esophagus and stomach Stomach divided into the rumen, reticulum, omasum and abomasums. Four chambers or three chambers depending on the animals Rumen: largest of the four stomachs Main fermanetation vat Two main types of microbes: fiver- (forage) disgesting and starch (feed grains) digesting bacteria Reticulum: intermediary connection between rumen and osum; secretes HCl for fermentation Osasum Absorb fatty acids, water, minerals, vitamins and carbohydrates Abomasums True stomach Process of digestion Physical process Once food enters the rumen, it gets fermented by microorganisms. Ruminants produce large quantities of saliva, which produces fluid for fermentation Sinks to bottom and new food goes on tope of it Regurgitated , swallowed again Biochemical Process of Digestion Do not have cellulose-digesting enzymes on their own Rely on symbiotic micorobes Produce cellulose enzymes which break down the cell walls of plant materials to release fatty acids into the gut that are absorbed by the ruminant Organisms are utimitally digested in the abomasums and nutrients are absortbed inth small intestine Double digestion Fermentation in the rumen makes much gas The digestive activity of symbiotic microbes present in the giestive tract play a major role in the diestion process and the upply of nutrients to the rumeninant. These microbes attack food particles and supply a major portion of the protient and energy to the ruminanat. Thus, the ruminants obtain nutrients and energy drom the digested microbes and form the volatile fatty acids procuded as a b-produc of the fermentation and digestion process Digestive Strateies of Omnivories: Nonhuman Primates Sacculated stomach Creates chambers for the fermentation of foliage by anaerobic bacteria It provides a buffer fluid between the two regions of the stomach to detoxify plant toxins with bacteria End result can digest and break down the cellulose and potentially toxi substances by gut bacteria more efficiently than any of th other primates Allow the colobine to eat items that would otherwise be poisonous Enlargement of the colon and small intestine Enlarging the digestive area of the large intestine Humans have ?large? intestines (long small intestine) and chimps have large colons Primate Taxonomy by Dietary Preference Insectivore-frugi-folivore Frugi-folvi Foli-frugi More from leaves than from fruits omnivore why primates search for animal food primate?s digestive system cannot extranct all of the essential amino acids and fatty acids from plant foods variability in capacity of the digestive system to extract amino acids 9/20 amino acids are important animal protein has all nine need for polyunsaturated fatty acid essential nutrients