chapter 17 digestive system system.pdfchapter 17 digestive system functions of digestive system •...
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Chapter 17 Digestive System
Functions of Digestive System • ingestion • mechanical digestion • chemical digestion • propulsion • absorption • defecation
Consists of the alimentary canal and accessory organs
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Alimentary Canal
About 8 meters long
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Movements of the Tube • mixing movements • segmentation • peristalsis
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Mouth
• ingestion • mechanical digestion (mastication) • prepares food for chemical digestion
• Parts • Cheeks • Lips • Tongue • Palate
• uvula
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Tongue
• Taste • Moves food • Forms bolus
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Palate
• roof of oral cavity • uvula
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Primary Teeth
• 8 incisors • 4 cuspids • 8 molars
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Secondary Teeth
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Salivary Glands
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Secretions of Salivary Glands
• Major salivary glands • Parotid glands • Submandibular glands • Sublingual glands
• Saliva • Moistens food particles • Helps bind the food particles together to form bolus • Begins chemical digestions of carbohydrates (salivary amylase) • Helps clean the mouth
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Pharynx
Connects nasal and oral cavities with the larynx and esophagus 3 parts • Nasopharynx • Oropharynx • Layrngopharynx
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Swallowing Mechanism
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Esophagus
Straight, collapsible tube about 25 cm long Carries food from pharynx to stomach Lower esophageal sphincter (cardiac sphincter) - controls the opening to the stomach
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Stomach
J-shaped, pouchlike organ 25-30 cm long 3 regions • Cardiac region • Fundic region • Body • Pyloric region
Wall contain three layers of muscle
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Lining of Stomach
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Gastric Secretions
• pepsinogen • from chief cells • inactive form of pepsin
• pepsin • from pepsinogen in presence of HCl • protein splitting enzyme
• hydrochloric acid • from parietal cells • needed to convert pepsinogen to pepsin
• mucus • from goblet cells and mucous glands • protective to stomach wall
• intrinsic factor • from parietal cells • required for vitamin B12 absorption
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Gastric Absorption
• some water • certain salts • certain lipid-soluble drugs • alcohol
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Mixing and Emptying Actions
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Pancreas
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Pancreatic Juice
• pancreatic amylase – splits glycogen into disaccharides • pancreatic lipase – breaks down triglycerides • trypsin, chymotrypsin, and carboxypeptidase – digest proteins • nucleases – digest nucleic acids • bicarbonate ions – make pancreatic juice alkaline
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Regulation of Pancreatic Secretions
• acidic chyme stimulates release of secretin • secretin stimulate release of pancreatic juice
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Liver Largest internal organ
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Liver Functions
• produces glycogen from glucose • breaks down glycogen into glucose • converts noncarbohydrates to glucose • oxidizes fatty acids • synthesizes lipoproteins, phospholipids, and cholesterol • converts carbohydrates and proteins into fats • deaminates amino acids • forms urea • synthesizes plasma proteins • converts some amino acids to other amino acids • stores glycogen, vitamins A,D, B12, iron, and blood • phagocytosis of worn out RBCs and foreign substances • removes toxins from blood • produces and secretes bile
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Composition of Bile
• water • bile salts
• emulsification of fats • absorption of fatty acids, cholesterol, and fat-soluble vitamins
• bile pigments • cholesterol • electrolytes
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Gallbladder Stores bile until it is released into the small intestine
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Regulation of Bile Release
• fatty chyme entering duodenum stimulate gallbladder to release bile
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Three Parts of Small Intestine Tubular organ 5.5 - 6.0 m long
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Intestinal Villus
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Wall of Small Intestine
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Secretions of Small Intestine
• peptidase – breaks down peptides into amino acids • sucrase, maltase, lactase – break down disaccharides into monosaccharides • lipase – breaks down fats into fatty acids and glycerol • enterokinase – converts trypsinogen to trypsin • somatostatin – hormone that inhibits acid secretion by stomach • cholecystokinin – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile • secretin – stimulates pancreas to release bicarbonate ions in pancreatic juice
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Absorption in the Small Intestine
• monosaccharides and amino acids
• through facilitated diffusion and active transport • absorbed into blood
• electrolytes and water • through diffusion, osmosis, and active transport • absorbed into blood
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Absorption in the Small Intestine
• fatty acids and glycerol • several steps • absorbed into lymph and blood
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Movements of the Small Intestine
• mixing movements • peristalsis – pushing movements • segmentation – ringlike contractions • overdistended wall triggers peristaltic rush resulting in diarrhea
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Large Intestine
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Functions of Large Intestine • little or no digestive function • absorbs water and electrolytes • secretes mucus • houses intestinal flora
• Absorbs vitamins K, B12, thiamine and riboflavin produced by the bacteria
• forms feces • carries out defecation
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Movements of Large Intestine
• slower and less frequent than those of small intestine • mixing movements • peristalsis • mass movements usually follow meals
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Feces
• water • electrolytes • mucus • bacteria • bile pigments altered by bacteria provide color • smell produced by bacterial compounds
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Life-Span Changes
• teeth become sensitive • gums recede • teeth may loosen or fall out • heartburn more frequent • constipation more frequent • nutrient absorption decreases • accessory organs age but the effects are less noticeable
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Clinical Application
Hepatitis • inflammation of the liver • most commonly caused by viral infection • can be caused by reactions to drug, alcoholism or autoimmunity
Signs and Symptoms • headache • low fever • fatigue • vomiting • rash • foamy urine • pale feces • jaundice • pain
Hepatitis A – not washing hands or eating raw shellfish Hepatitis B – chronic; serum Hepatitis C – serum Hepatitis D – very severe; only produces symptoms if infected with B; serum Hepatitis E, F, G – more rare
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Clinical Application
Ulcers • Sores in the lining of stomach • most commonly caused by helicobacter pylorus • can be caused by reactions to drug and certain foods
Signs and Symptoms • pain • Blood in feces
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Clinical Application
Gastric Reflux Disorder • recurrent heartburn • Can cause the lining of the esophagus to wear away • Treat with acid reducers and/or surgery
Signs and Symptoms • pain