Download - The Digestive System
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The Digestive System
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The Digestive System
4 steps for processing nutrients from food1. Ingestion2. Digestion3. Absorption4. Elimination
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Ingestion & DigestionIngestion: Eating or drinking
Digestion: the breaking down of food into molecules that are small enough to be absorbed by the body
Mechanical digestion: Chewing and grinding food into smaller pieces, increasing the surface area
Chemical digestion: Breaking chemical bonds of macromolecules (carbs, proteins and lipids) into monomers (sugars, amino acids, glycerol & fatty acids)
• Hydrolysis reactions that are carried out by enzymes
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Absorption & EliminationAbsorption:• Cells absorb small molecules (monomers)
allowing them to enter into the circulatory system for immediate use or be transported to storage organs for later use
Elimination: • Removing undigested waste (feces)
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Digestive SystemDigestive Tract
– A.k.a. an alimentary canal (2 openings)
– The mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Accessory Glands & Organs– Aid in digestion, but not a part of
the digestive tract– Salivary glands, pancreas, liver,
gallbladder. – Secrete digestive juices and
enzymes into the digestive tract
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What’s Your Size?Predicted Length
(m)Actual Length
(m)Mouth 0.15Pharynx 0.05Esophagus 0.25Stomach 0.25Duodenum 0.2Jejunum 2.8Ileum 4.2Large Intestine 1.5Total ~9
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Mouth• Plays a role in ingestion and
digestion• Teeth, tongue, hard palate aid in
mechanical digestion• Tongue moves food down to the
esophagus• Salivary glands aid in chemical
digestion– Release saliva (~1L/day), a watery liquid
containing digestive enzymes– Salivary amylase begins to break down
starch into smaller carbohydrates– Lubrication Chewed up food is now
called a bolus
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Esophagus• Located behind the trachea• As you swallow, the epiglottis
closes over the trachea and the food bolus passes through pharynx into the esophagus
• The bolus is pushed through the esophagus by a series of muscle contractions called peristalsis
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Heart Burn
• After food passes into the stomach, the cardiac sphincter closes the esophagus
• If the sphincter opens at an inappropriate time, stomach acid can flow back into the esophagus
• Esophagus does not have the same protective lining as the stomach
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Stomach• Elastic, muscular sac with
a protective lining that contains millions of gastric glands
• Can ~ 2 L• Mechanical and chemical
digestion
I ate too much…I’m STUFFED!
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StomachChemical Digestion:• The hormone, gastrin, stimulates gastric glands to
release gastric juice – Hydrochloric acid breaks apart cells and kills bacteria– Enzymes e.g. pepsin– Mucus lubrication and protection
Mechanical Digestion:• Stomach muscles churn• Bolus becomes an acidic,
nutrient-rich liquid called chyme
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Small Intestine• Chyme passes through the pyloric sphincter
and enters the small intestine (peristalsis)• Long, narrow tube where digestion is
completed and absorption begins• 3 parts:
– Duodenum– Jejunum– Ileum
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Duodenum• Bile from the liver and gallbladder are
secreted into the duodenum to help with lipid digestion
• Pancreas secretes pancreatic juice into the duodenum– Neutralizes acidic chyme– Pancreatic amylase – Trypsin & chymotrypsin (protein digestion)– Pancreatic lipase
• Small intestine releases enzymes too
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Jejunum & IleumJejunum• Contains more villi, therefore
more absorption• Breakdown of remaining
polypeptides and carbohydrates
Ileum• Absorption• Push remaining undigested
material into the large intestine
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Large Intestine• Undigested material passes through the sphincter
between the ileum and the cecum• Absorption of water and dissolved minerals• Intestinal bacteria produce vitamins• Indigestible material (feces) passes through the
rectum to the anus– Anal sphincters help control timing of elimination
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Increased Surface Area• The small and large
intestine are folded to surface area and therefore absorption
• Within the folds, there are finger-like projections called villi– Lacteal absorbs fats and fat-
soluble vitamins– Capillaries absorb glucose,
amino acids, minerals and water-soluble vitamins
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Regulation of Digestive Processes
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• http://www.neok12.com/php/watch.php?v=zX680f4e7e6e7c420f746402&t=Digestive-System
• http://www.neok12.com/quiz/DIGSYS04• http://www.neok12.com/quiz/DIGSYS01• http://www.neok12.com/diagram/Digesti
ve-System-01.htm