the human body: the digestive system textbook chapter 35 review book topic 1
TRANSCRIPT
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The Human Body:The Digestive System
Textbook Chapter 35Review Book Topic 1
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Function
• Ingest (eat) food
• Breaks food down to absorb nutrients
• Eliminates what cannot be digested as waste
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Ingestion• Mechanical digestion – involves
physical breakdown of food into smaller pieces
• Teeth and tongue in the mouth
• Smooth muscles in the stomach
• Smooth muscles in the small intestines
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• Chemical digestion – enzymes are used to break down large molecules into smaller molecules that can be absorbed by cells
• Ex. Amylase – enzyme found in saliva which causes the breakdown of starches into sugars
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Esophagus
• As the tongue pushes chewed food to the back of the mouth, the swallowing reflex is stimulated
• Esophagus connects the mouth to the stomach
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• Lined with smooth muscles that contract rhythmically to move food through the digestive system in a process called peristalsis
• Continues throughout the digestive tract
• Not even affected by gravity….you could still digest food upside down!
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• When a person swallows, the epiglottis covers the trachea (windpipe)
• If food enters the windpipe, choking occurs
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Stomach• A sphincter, a circular muscle, controls the
movement of food from the esophagus into the stomach
• Stomach walls are composed of three layers of smooth muscle
• Involved in mechanical digestion and chemical digestion
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• Very acidic environment
• Gastric glands secrete an acidic solution at pH 2
• Any leakage of stomach acid through the sphincter muscles can cause acid to reach the esophagus, causing heartburn
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• Pepsin – enzyme involved in the chemical digestion of proteins in the stomach
• Cells in the lining of the stomach secrete mucus to help prevent stomach acid from digesting the stomach’s cells
• Some substances like alcohol and aspirin are absorbed by stomach cells (but most absorption occurs in the small intestine)
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• When empty, stomach capacity is about 50 mL
• When full, it can expand to 2 – 4 L
• Muscular stomach walls contract and push food farther along the digestive tract
• Empties through another sphincter into the small intestine
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Small Intestine• 7 m in length
• Longest part of the digestive system
• Small intestine because the diameter is 2.5 cm compared to the diameter of the large intestine at 6.5 cm
• Smooth muscular walls continue the process of mechanical digestion and peristalsis
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• Chemical digestion is completed by accessory organs
• Pancreas
• Produces enzymes that digest carbohydrates, proteins, and fats
• Produces hormones
• Secretes an basic solution to raise the pH in the small intestine to pH 7 (neutral) for the optimum environment for enzyme action in the small intestine
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• Liver• Largest internal organ of the body
• Produces bile which breaks down fats
• About 1 L of bile is produced each day and any excess is stored in the gall bladder
• Gall bladder• Stores excess bile
• Releases bile into the small intestine when needed
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• Nutrients from food are absorbed from the small intestine into the bloodstream through villi
• Fingerlike projections
• Increase the surface area of the small intestine
• Gives the small intestine as much absorption room as a tennis court!
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• When digestion is complete, any remaining food, in the form of chyme moves into the large intestine
• Chyme is a semi-liquid solution composed of materials that cannot be digested or absorbed by the small intestine
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Large Intestine• End portion of the digestive tract
• 1.5 m long
• Includes the colon, rectum and appendix
• Colon normally contains bacteria which produce vitamin K and some B vitamins
• Primary function is to absorb water from chyme
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• Indigestible material becomes more solid as water is absorbed, forming feces
• Peristalsis continues to move feces to the rectum
• Walls of the rectum to stretch initiating a reflex
• Final sphincter muscle to relaxes, eliminating the feces from the body through the anus
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Digestive Structure Primary Function Time Food in Structure
Mouth Mechanical and chemical digestion
5-30 seconds
Esophagus Transport (swallowing)
10 seconds
Stomach Mechanical and chemical digestion
2-24 hours
Small Intestine Mechanical and chemical digestion
3-4 hours
Large Intestine Water absorption 18 hours – 2 days
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Nutrition• Nutrition – process by which a person takes in
and uses food
• Food supplies building blocks and energy needed by the body to maintain body mass
• Daily input of energy from food should equal the amount of energy a person uses daily
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• Calorie – unit used to measurethe energy content of food
• 1 calorie is the amount of heat needed to raise the temperature of 1 mL of water by 1°C
• Can be found by burning the food and converting its stored energy to heat
• To lose weight, more calories must be used than consumed
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• Carbohydrate• Ex. cereal, pasta, potatoes,
strawberries, rice
• Broken down into simple sugars
• Stored in the liver in the form of glycogen
• Cellulose – a plant starch – cannot be digested but is required by humans to “flush” out and keep the digestive tract clean (also known as fiber)
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• Fats• Essential for your diet in proper amounts
• The most concentrated energy source available to the body
• Protect internal organs
• Maintain homeostasis by providing energy, storing and transporting certain vitamins
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• Not all fats are beneficial
• Saturated (solids)• Ex. Meats, cheeses, dairy• “Unhealthy”• Can result in high blood pressure or heart
problems
• Unsaturated (liquids)• Ex. Plants• “Healthy”
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• Digested in small intestine
• Broken down into fatty acids and glycerol
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• Proteins• Basic structural components of all cells
• Made up of amino acids• Absorb into the blood and are “rebuilt” when they
enter body cells
• 20 amino acids • 8 of these we cannot make in our body and
must obtain them from our food
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• Form enzymes, hormones, neurotransmitters, membrane receptors
• Ex. Animal byproducts: meat, fish, poultry, eggs, dairy
• Ex: Plants (only cover some of the essential amino acids needed…ex. beans + rice)
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• Food Pyramid
• Changed in 2005 by the Department of Agriculture
• Shows which foods and the amount of these foods is right for your diet
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Old Food Pyramid
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Modern Food Pyramid
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• Vitamins and Minerals
• Vitamins – organic compounds needed in small amounts for metabolic activities
• Help enzymes function
• Obtained by your diet, cannot be made in large enough quantities by your body
• Some can be stored in your liver but many cannot
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• Minerals – inorganic compounds used as building materials an involved in some metabolic functions
• Taking over the recommended daily amount of vitamins or minerals can be dangerous
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• Nutrition Labels• Provided on commercially packaged foods
• Based on a diet of 2000 calories a day
• Required information:• Name of food• Net weight or volume• Manufacturer information• Ingredients• Nutrient content