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Digestion and Nutrition - 2013
Overall Goal of Digestive Systems A. Obtain organic molecules from environment B. Reduce complex molecules such as proteins, polysaccharides, nucleic acids and lipids to absorbable sizes and C. Transport the molecules into the blood stream so that they may be assimilated into cells.
General Strategies for obtaining nutrientsA. Filter feeders - microorganisms, marine and freshwater crustaceans, baleen whales. (show whale video)http://videos.howstuffworks.com/discovery/428-corwins-quest-whales-video.htm
http://videos.howstuffworks.com/discovery/28113-assignment-discovery-baleen-whales-plates-video.htm
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B. CarnivoresC. Herbivores 1. the problem with cellulose - requires bacteria or protozoa that produce cellulase 2. pregastric fermentation 3. postgastric fermentationD. OmnivoresE. Symbiotic nutritionchloroplasts from algae in the bodies of sea slugs - photo synthetic products feed slugshttp://www.newscientist.com/article/dn16124-solarpowered-sea-slug-harnesses-stolen-plant-genes-.html
bacteria in digestive tracks of ruminants (cows)http://www.teachersdomain.org/resource/nat08.living.str.living.digest
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Perspectives on Digestion
OverviewMechanical - mastication, stomach, crop, and intestinal motilityChemical (secretions) - enzymes from saliva, pancreas and intestinesAbsorption - intestinal lumen o bloodAssimilation - blood into cells throughout the body.
MotilitySmooth musclePace setter potential - specialized cells in digestive tract produce electric impulses(potentials) that stimulate the gut to contract
Enteric (intrinsic) nervous control (responds to stretch, pH, hormones)Extrinsic = controlled by central nervous system (brain & spinal cord)
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Fig. 14-5, p.619
Intrinsic Nerves of the Rat’s Stomach
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Motility
Storage of waste
Defecation
Secretions
IngestionMouth
Pharynx Receiving
Foregut
Crop
ConductingStorageDigestion
Midgut (stomach)Digestion (acidic)
Hindgut
Digestion (basic)Absorption
Assimilation
Fig. 14-1, p.613
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The enzyme “cellulase” is required to hydrolyze cellulose. This enzyme is only produced by microorganisms. Animals must provide organs that support the growth of these symbionts.
Starch is hydrolyzed to maltose by the enzyme “amylase” which is produced by the salivary glands and the pancreas.
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Hydrolysis of a disaccharide (maltose) to two monosaccharides (glucose)
Maltase is the enzyme that performs this action. It is produced primarily by the cells that line the intestinal lumen.
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Categories of Digestive Enzymes
Amylase: starch hydrolysis to maltose
Protease: proteins hydrolyzed to peptides
Lipase: triglycerides hydrolyzed to fatty acids and glycerol
Nucleotidases nucleic acids hydrolyzed to nucleotides
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Gastrointestinal Tract (alimentary canal) mouth-anus
Accessory Organs Liver Gall Bladder Pancreas
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Fig. 14-7a, p.624
Tongue
(a)
Trachea
Esophagus
Epiglottis
Pharynx
Uvula
Soft palate
Hard palate
Nasalpassages
Glottis at entrance of larynx
Bolus
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Peristalsis - a local reflex
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Fig. 14-8, p.627Duodenum
Smoothmuscle
FundusEsophagus
Gastroesophagealsphincter
Body
Stomachfolds
Oxynticmucosa
AntrumPyloricglandarea
Pyloricsphincter
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Table 14-3b, p.632
Gastricpit
Mucosa
Submucosa
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Table 14-3c, p.632
Gastric gland
Surface epithelial cells
Gastricpit
Chief cells
Mucous cells
Enterochromaffin-Like (ECL) cells
In oxyntic mucosa
Parietal cells
Produce pepsinogen
Produce HCl andIntrinsic Factor
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Peptic Ulcers
Heliobacter pylori - bacterial infection responsible for 90%of all peptic ulcers
Treatment with antibiotics
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Fig. 14-11, p.634
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HCl, fats, osmo
CCK
Secretin
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Intestinal Cross Section
Layers of the alimentary canalSerosa
Muscularis
Submucosa
Mucosa
Smooth muscle cells
Villus (Villi)
Microvilli
Mucosal cells
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Fig. 14-20, p.647
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Large fat droplet
Lipid emulsion
Small lipid (fat) droplet with bile salt moleculesadsorbed on its surface
Lipid-soluble portion(derived from cholesterol)
Negatively charged H2O-soluble portion (a carboxyl group at the end of a glycineor taurine chain)
Through action of bile salts
Fig. 14-17, p.644
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Fig. 14-24a, p.654
Lipid Absorption
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Fig. 14-14, p.641
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Fig. 14-16, p.642
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Block Diagram of Lipid Absorption
Lipids in Duodenum
Lipids combine with Bile and form Micelles
Micelles taken up by mucosal cells
Mucosal cells add proteins and extract fatty acids
Lipase begins to convert triglycerides to fatty acids
Lipids enter lymph capillaries as Chylomi ra
Chylomicra move through lymphatic system and enter the blood at subclavian veins.
Liver takes up Chylomicra and converts them to HDL’s and LDL’s
HDL’s and LDL’s re-enter blood and are distributed to other cells throughout the body.
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Fig. 14-26, p.657
Transverse colon
Internal anal sphincter(smooth muscle)
Taeniae coli
Ileocecal valve
Ascending colon
RectumCecum
Appendix
Anal canal
External anal sphincter(skeletal muscle)
Sigmoid colon
Descending colon
Haustra
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Fig. 14-27b, p.661
Reticulum
(b)
To smallintestine
Rumen
Abomasum
Omasum