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DIGESTIVE SYSTEM Professor Andrea Garrison Biology 11
Illustrations ©2010 Pearson Education, Inc.
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Digestive System Digestive system = digestive tract plus associated glands and organs Function = digestion Breaks down food to simple molecules that can be absorbed by the lining of the intestine Digestive System
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Glands in lining of stomach and intestine
Digestive System
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Stages of Digestion Digestive System
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Stages of Digestion Digestive System
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Stages of Digestion Digestive System
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Stages of Digestion Digestive System
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Ingestion Digestive System
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Digestion Mechanical digestion Chemical digestion
Breaks chunks of food into small pieces Allows chemical digestion to be effective Chemical digestion Digestive enzymes and assisting chemicals break food into smaller molecules for absorption Digestive System
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Glands in lining of stomach and intestine
Digestive System
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Digestion in Mouth Mouth Ingestion Mechanical digestion Food is chewed
Pressure on gums creates reflex Bolus is formed by tongue, teeth, cheeks Digestive System
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Digestion in Mouth Mouth Chemical digestion
Taste buds detect sweet, sour, salty, bitter Clue to spoiled food Smell, sight, taste of food prepares stomach Digestive System
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Digestion in Mouth Mouth Chemical digestion
Salivary glands secrete saliva Parotid glands Sublingual glands Submandibular glands Saliva 99% water 1% salts and proteins Mucins produce mucus Amylase breaks down starch Digestive System
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Swallowing Bolus pushed to pharynx to esophagus
Food swallowed via reflex in pharynx Digestive System
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Swallowing Bolus pushed to pharynx to esophagus
Food swallowed via reflex in pharynx Digestive System
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Swallowing Bolus pushed to pharynx to esophagus
Food swallowed via reflex in pharynx Digestive System
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Peristalsis Food moves through digestive tract from esophagus to anus via peristalsis Waves of involuntary muscle contractions Push materials forward Different rates in different regions of digestive tract Triggered by stretch of muscular walls as material moves in Digestive System
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Esophagus Muscular tube from pharynx to stomach
Esophageal sphincter at top Penetrates diaphragm Digestive System
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Stomach Sphincters keep food and gastric juices in stomach until desired release Cardiac sphincter Prevents backflow into esophagus Pyloric sphincter Controls movement into small intestine Digestive System
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Stomach -- Digestion Serves for: Food storage Formation of chyme
Slurry of food, mucus, gastric enzymes Initiation of protein digestion Digestive System
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Stomach -- Digestion Muscles of stomach wall contract to mix the chyme
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Stomach -- Digestion Gastric glands secrete mucus, pepsin, acid
Very acidic Deactivates salivary amylase Acid + pepsin breaks down proteins → amino acid chains Digestive System
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Small Intestine Peristalsis in stomach and relaxation of pyloric sphincter Chyme enters small intestine a little bit at a time Small intestine Digestive System
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Small Intestine 3 sections Duodenum -- first 10 inches
Jejunum -- 8 feet Ileum --12 feet Small intestine Digestive System
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Small Intestine -- Digestion
Chyme Carbs have barely started digestion Protein segments from stomach digestion Fats not yet digested Digestive System
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Small Intestine -- Digestion
Role of liver Produces bile to assist in fat digestion Role of gall bladder Stores bile from liver Role of pancreas Produces bicarbonate Produces digestive enzymes Digestive System
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Small Intestine -- Digestion
Duodenum receives Chyme Mucus from intestinal cells Secretin and CCK from glands in intestinal lining Stimulate liver, gallbladder and pancreas Bile from liver via gallbladder Bicarbonate from pancreas Digestive enzymes from pancreas Digestive System
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Small Intestine -- Digestion
Bicarbonate neutralizes acid Bile emulsifies fats Increases surface area for digestive enzymes Fat Digestive System
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Small Intestine -- Digestion
Pancreatic enzymes work once pH neutralized Pancreatic amylase Digests carbohydrates to monosaccharides (sugars) Proteases Digest proteins to amino acids Lipases Digest fats to fatty acid + glycerol Digestive System
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Small Intestine -- Digestion
(protease) Digestive System
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Small Intestine -- Digestion
(protease) Digestive System
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Small Intestine -- Digestion
Digestive System
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Small Intestine -- Digestion
Digestive System
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Small Intestine Most of absorption occurs here Maximizes surface area
Folds, folds, more folds Villi and microvilli most abundant in duodenum and jejunum, also present in ileum Digestive System
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Small Intestine Digestive System
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Small Intestine Digestive System
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Small Intestine Digestive System
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Absorption Most of water Amino acids & sugars Fats
actively transported into cells and then to blood capillaries Fats Diffuse into cells Built back into triglycerides Attached to proteins (lipoproteins) Expelled via exocytosis Absorbed into lymphatic vessel and carried to blood Digestive System
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Ulcer-causing Bacteria
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What’s left? Mostly wastes Some water
Never absorbed into cells of body Exception is bile, made from breakdown products of red blood cells Some water Will be absorbed in large intestine Digestive System
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Ileocecal Sphincter Peristalsis moves materials into large intestine
Small intestine joins large intestine at ileocecal sphincter Digestive System
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Large Intestine Large intestine Colon Rectum Anus Ascending colon
Transverse colon Descending colon Sigmoid colon Rectum Anus Transverse colon Ascending colon Sigmoid colon Descending colon Rectum Anus Digestive System
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Large Intestine -- Absorption
Large anaerobic bacteria population (E. coli) Breaks down remaining nutrients Synthesize some B vitamins and vitamin K absorbed in large intestine Digestive System
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Large Intestine -- Absorption
Most remaining water absorbed Prevents dehydration Peristalsis too fast Diarrhea Peristalsis too slow constipation Digestive System
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Egestion Peristalsis moves wastes into rectum
Stretch of rectal walls triggers urge to defecate Wastes removed from body through anus 2 sphincters Internal anal sphincter -- involuntary External anal sphincter -- voluntary Digestive System
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