dinner is served remember the last time you sat down to a dinner of your favorite foods? recall...
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• Dinner Is Served
• Remember the last time you sat down to a dinner of your favorite foods? Recall everything that you did before you swallowed your first bite.
1. Why do you cut up your food?
2. What role do your teeth play in eating?
3. Saliva is the fluid that is found in your mouth. What role do you think it plays in eating?
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Chapter Chapter 38.238.2The Process of Digestion
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Main Function
Helps convert foods into simpler molecules that can be absorbed and used by the cells of the body
Built around a one-way tube (alimentary canal) that runs through the body
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Organs of the Digestive System
The path that food travels: Mouth pharynx esophagus
stomach small intestine large intestine rectum anus
Several major accessory structures including the salivary glands, the pancreas and the liver add secretions to the digestive system.
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Digestive System
Mouth
Salivary glands
Stomach
Pancreas (behind stomach)Large intestine
Small intestine
Rectum
Gallbladder (behind liver)
Liver
Esophagus
Pharynx
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The Mouth
Beginning of the digestive system
Mechanical digestion physical breakdown large pieces into smaller pieces Chewing – Teeth: cut, tear, crush food Purpose is to increase surface area of food so
that more enzymes can breakdown the molecules
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The Mouth (Cont’d)
Chemical Digestion large food molecules are broke down into smaller food molecules Enzymes, acid
Salivary glands – produce saliva Moistens food Contains enzymes
Amylase breaks down starches and releases sugars
Lysozyme fights infection
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Swallowing
Food is pushed to the back of the throat While chewing, the tongue pushes food up
and back Smashes food against the hard and soft
pallet Clump of food bolus
Epiglottis flap of tissue that blocks off the opening to the trachea, directing the food down the esophagus
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Esophagus Food tube
Connects pharynx and the stomach
Peristalsis contractions of the smooth muscle squeeze the food through the esophagus into the stomach Fig. 38-11 page 980
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Stomach
Large muscular sac Site of chemical and mechanical digestion Contracts to churn and mix stomach fluids
together
Cardiac sphincter – Ring of muscle that lets food into the stomach
and prevents acid from entering the esophagus
Heartburn painful, burning sensation, that results from the backflow of stomach acid
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Stomach (cont’d)
Contains gastric glands Produce mucus – protects the stomach Produce hydrochloric acid - keeps stomach
pH acidic Produce pepsin – digests proteins
Works best in acidic conditions
Mixture of stomach fluids and food chyme
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Small Intestine
3 parts: duodenum, ileum, jejunum Pyloric sphincter – separates stomach
and small intestine
Functions: Complete chemical digestion Absorb nutrients
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Pancreas
Pancreas and gall bladder release enzymes/fluids into small intestine
Pancreas Produces hormones that regulate blood sugar Produces enzymes that breakdown all the
macromolecules Produces sodium bicarbonate – neutralizes
stomach acid and allows enzymes to function properly
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Gall Bladder
Gall bladder releases bile into the small intestine
Bile loaded with lipids and salts Acts as a detergent to breakdown fats Produced in the liver
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Villi
Villi – fingerlike projections on the inside lining of the small intestine Covered by microvilli Provides an enormous surface area for
the absorption of nutrient molecules Once food is ready to leave it is
nutrient free Only cellulose, water, and other
indigestible substances remain
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Large Intestine
3 parts: ascending colon, transverse colon, descending colon
Contains bacteria that aids digestion
Functions: Transports waste Absorbs water
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Enzymes in DigestionSite
Mouth
Stomach
Small intestine(from pancreas)
Small intestine
Site
Mouth
Stomach
Small intestine(from pancreas)
Small intestine
EnzymeEnzyme Role in DigestionRole in Digestion
Salivary amylase
Pepsin
Amylase
Trypsin
Lipase
Maltase, sucrase, lactase
Peptidase
Breaks down starches into disaccharides
Breaks down proteins into large peptides
Continues the breakdown of starch
Continues the breakdown of protein
Breaks down fat
Breaks down remaining disaccharides into monosaccharides
Breaks down dipeptides into amino acids.
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Digestive System Disorders
Peptic ulcers Acids released by the stomach damage the
organ’s own lining, producing a hole Caused by Helicobacter pylori – bacteria
Diarrhea Not enough water is absorbed
Constipation Too much water is absorbed