Chapter 2 - Ingestion to Energy Metabolism Chapter 2...

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Ingestion to Energy Metabolism Chapter 2
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Breaking down foods in order for them to be absorbed by the cells of the gastrointestinal tract (GI tract). Over 25 feet long Mouth salivary glands esophagus stomach pancreas liver gall bladder small intestine large intestine rectum anus
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Digestion – breaking food down 1. Mastication 2. Enzymatic activity Absorption Transport Assimilation and/or energy production
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Mouth (oral cavity) Esophagus Stomach Small intestine Large intestine Rectum
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Mastication Increases exposed areas of food Facilitates enzyme action Salivary glands – secretes saliva with digestive enzymes Amylase Moisten Initiates enzymatic digestive process First step of digestion Once the food is broken down and chewed, its called ‘bolus’
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The bolus is passed through the esophagus Connects the oral cavity (mouth) to the stomach Little digestion occurs here – passes too quickly
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Digestion Muscular organ Mix/churn food - peristalsis waves Digestion is primary function, little absorption Major secretions Hydrochloric acid Mucus Digestive enzymes Food is in contact with acids and enzymes – continues digestion Digested in stomach for about an hour The bolus is considered chyme, once in the stomach
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Digestion and absorption Makes up majority of GI tract, about 20 feet long Walls lined with villi Small, rod like/hair projections that are attached to walls Villi has blood and lymphatic supply – nutrients have access to circulatory system The combination of the length and the villi = large surface area to absorb nutrients Divided into three sections 1. duodenum 2. jejunum 3. Ileum
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The partially digested food enters the duodenum first Short section, about 1ft Contact with more digestive enzymes secreted from gall bladder and pancreas Majority of digestion occurs here, making it ready for absorption
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Jejunum (2 nd ) Little digestion occurs here majority absorption Ileum (3 rd ) Majority absorption
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Absorption Colon Rectum Anus Takes about 18 – 24 hrs to pass Some absorption – water, sodium, chloride, potassium and vit K Contents are contacted with bacteria Continues to digest Produces intestinal gases Produces some vitamins too
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Passive diffusion Molecules pass through membranes that are permeable by concentration gradients only Facilitated diffusion Protein molecules carry substances across membranes that are dictated by conc gradients (high low) Active transport
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Chapter 2 - Ingestion to Energy Metabolism Chapter 2...

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