the digestive system
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The Digestive System. Nutrition. Diet = everything you eat Proper diet . 10% Protein ______________. 30% fat ____________________. 60% carbohydrates. Carbohydrate Primary energy source for cells Cereals, grains, breads, fruits, vegetables - PowerPoint PPT PresentationTRANSCRIPT
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The Digestive System
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Nutrition• Diet = everything you eat• Proper diet
10% Protein______________
30% fat____________________
60% carbohydrates
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• Carbohydrate–Primary energy source for cells–Cereals, grains, breads, fruits, vegetables
–4 calories per gram
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• Protein–Use as building block for cell structures, enzymes, hormones, muscle, bones
–Dairy products, poultry, fish, meat, grains
–4 calories per gram
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• Fat–Use to construct cell
membranes & other cell structures, insulate
nervous tissue, energy source, fat-soluble vitamins (A, D, E, K)
–Oils, margarine, butter–9 calories per gram
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• Rule of balancing diet & activity–Energy obtained from food – energy used by body’s cells = energy stored in fat
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Other compounds needed
• Only obtained through food eaten
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Amino acids
• 8 of 20 amino acids the body cannot produce – must be eaten
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Vitamins• Body requires in small
amounts for normal growth & activity
• Used as components of cellular enzymes or coenzymes
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• Water soluble – soluble in water, body doesn’t store• ex: thiamin, niacin,
ascorbic acid, folic acid
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• Fat soluble – soluble in fat –Excessive amounts accumulate in body’s fatty tissue & can reach toxic levels
–A, D, E, K
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• Trace elements – minerals that are required by the body– present only in minute amounts–They are also required for plant growth so they are usually obtained by eating salads
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Digestion
• Food molecules are broken down by enzymes (amylases)
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Fats• Insoluble in water
–Aggregate into large globules consisting of many fat molecules
–Not easily attacked by enzymes
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• Emulsification – breaks up fat globules into tiny fat droplets–bile salts emulsify fats–produced in liver
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• Lipases – break fat molecules into fatty acids and glycerol
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Proteins
• Folded into tight balls or wound together into tough fibers
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–Enzymes cannot break down these balls & fibers because they cannot get at the individual protein chains
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• Protein digestion – 2 steps:1.Hydrochloric acid (HCl) in
stomach unfolds large proteins
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2.Enzymes (proteases) break down single polypeptide strands
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Starch• Broken down into sugars
by enzymes (amylase)
Starch-binding domain of ß-amylase
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Structures of the Digestive System
• Mouth–Teeth rip or chew food into shreds
–Tongue mixes it with watery solution called saliva
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•saliva is secreted into mouth by 3 pairs of salivary glands
•Moistens and lubricates food so it is swallowed easier
•Contains amylase – begins breakdown of starch
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• Pharynx–Food passes through
• Esophagus–Long tube that connects the mouth to the stomach
–No digestion takes place
–About 25 cm long
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–Food is pushed down the tube•Peristaltic contractions – successive rhythmic waves of contraction of the smooth muscle wall of the esophagus
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• Stomach –Passes from esophagus into stomach through a valve called a sphincter•Prevents acid soaked food from going back into esophagus
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–When food enters stomach, gastric juice is secreted by stomach lining•Gastric juice – HCl and acid stable proteases
•Mixture of food and gastric juice is called chyme
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–Stomach mixes contents by contraction and relaxation of muscular wall
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• Small intestine–Only small amounts of
chyme pass into smallintestine so that acid
can be neutralize
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–Some digestive enzymes secreted by cells of intestinal walls
–Most digestive enzymes produced in pancreas•Sends enzymes through duct into first part of small intestine (duodenum)
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• Small intestine is around 6 m (19.8 ft) long
• Complete digestion of carbohydrates, fats, and proteins in duodenum occurs in first 25 cm
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• Lining covered with fingerlike projections called villi– increase surface area for more absorption
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• Fluid absorption is about 99%–Average human consumes about 0.85 liters of solid food and 1.2 liters of water/day
–With food, water, and digestive secretions, about 9 liters pass through/day
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–Only about 0.05 liters of solid and 0.1 liters of liquid leave body as waste
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• Large intestine (colon)–About 1 m long–No digestion takes place
•Small amount of fluid, sodium, and vitamin K are absorbed
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–Primary function – trash compactor•Undigested food (plant fiber and cellulose) is compacted and stored
•Bacteria help process into feces
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–Final segment of colon is called the rectum•Compacted material passes through by peristaltic contractions
•From rectum exits body through anus
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Nutrients delivered to cells• Blood that leaves small intestine is rich with products of digestion–Collected in portal vein and goes to liver
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1. Supplies quick energy by releasing sugar into bloodstream
2. Builds complex carbohydrate from sugar
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3. Makes protein from amino acids
4. Stores vitamins and minerals
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5. Produces bile salts
6. Regulates blood clotting
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7. Monitors cholesterol production
8. Detoxifies alcohol and poisons