9.5 Digestion in the Small and Large Intestines
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Transcript of 9.5 Digestion in the Small and Large Intestines
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9.5 Digestion in the Small and Large Intestines
Pages 412-420
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Small intestine
• Site of digestion of carbohydrates, lipids and protein
• Food passes through in 3-5 hours
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Dimensions of Small Intestine
• Diameter 2.5 cm• 7 m long
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Sections
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Duodenum
• First section• 25-30 cm• Digestive enzymes added• Acid is neutralized
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Jejunum
• Digestion and absorption
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ileum
• absorption
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Villi and microvilli
• Finger-like projections increase the surface area for absorption
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Where the food goes
• Sugars, amino acids, water-soluble vitamins and minerals go into capillaries
• Fats go into lacteal lymphatic system bloodstream
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Chemical Digestion
• Pyloric sphincter regulates movement of chyme into the small intestine
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Pancreas
• Produces digestive enzymes which pass through pancreatic duct.
Ex. more amylase for carbs
• Produces insulin
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Cholesystokinin, CCK, from duodenum lining prompts pancreas to secrete
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Secretin
Prosecretin secretinacid
Functions - stimulates liver to secrete bile- stimulates pancreas to secrete enzymes-stimulates pancreas to secrete HCO3
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- change in pH inactivates pepsin-regulates rate
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trypsinogen
enterokinasetrypsinogen trypsin
Further digests long-chain protein into short-chain protein
Enzmes: carboxypeptidase and erepsin break protein segments down into amino acids
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Fats
• Too big for enzyme lipase• Bile emulsifies fats…micelles
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Liver
• Liver detoxifies blood,• Glycogen manufacture and storage, vitamins• Produces bile
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Absorption
• Simple Diffusion• Fascilitated Diffusion• Osmosis• Active Transport
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Large intestine
• 1.5 m in length• 7.6 cm diameterCecum, colon, rectum and anusColon: ascendingtransversedescending sigmoid
Rectum: last 20 cm
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Functions of large intestine
• Absorbs water (20L per day)• Vitamins B and K, and Na+ and Cl-
• 4-72 hours• 500 species of bacteria (gas)
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Cellulose and Fibre
• Bulk• Full-feeling lasts longer
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Anus
• Defecation reflex-eliminated feces• 1st sphincter, the internal anal sphincter is a
smooth muscle (involuntary)• 2nd sphincter, the external anal sphincter is
made of skeletal muscle and is voluntary• Both muscles must be relaxed for defecation
to happen
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Endoscopy
• Light, lens and camera• Through anus, mouth or opening in the
abdomen• Diagnosis: biopsy• Treatment: surgery
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