lecture 2 digestion handouts - The digestive system 25-1...

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The digestive system 25-1
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What nutrients do we extract from food and why? In addition to oxygen that we breathe in, we require the following nutrients: • Water (to maintain hydration, perform hydrolysis reactions) • Amino acids (energy source, make proteins) • Sugar (energy source, make carbohydrates) • Fatty acids (energy source, make lipids) • Salts (_____________________, and chemical reactions) Why do we need to be able to make proteins, lipids, and carbohydrates? 25-2
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What needs to be done to food in order to extract these nutrients? • Mechanical (physical) digestion- shredding/crushing food to open up cells and make cellular contents more readily available for chemical digestion • chemical digestion- dissolving / breaking down food with acids and enzymes so nutrients are in a form that is readily absorbable and usable. _____________________________ ___________________________________ _____________ • After mechanical and chemical digestion is
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complete, nutrients are absorbed and then transported to cells by the bloodstream and in the case of lipids, the lymphatic system. 25-3
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For mechanical (physical) digestion: • Teeth, tongue, and cheeks: In the mouth, teeth tear off a portion of food and then shred and crush it (with the tongue positioning food) in a process called mastication. • In the stomach, muscular contraction churns food into a paste called chyme. This mechanical process increases the efficiency of chemical digestion. • Peristalsis is the movement of food through the digestive tract ___________________________________ ___. 25-4
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Chemical digestion: • a series of hydrolysis reactions that breaks dietary macromolecules into monomers (small molecules that are readily absorbable). – Digestive enzymes produced by salivary glands, stomach, pancreas and small intestine hydrolyze: • polysaccharides into monosaccharides • proteins into amino acids • fats into monoglycerides and fatty acids • nucleic acids into nucleotides (In other words, enzymes ________________________________________ ____________________________________ in order to ease absorption.) • Some nutrients are present in a usable form in ingested food and do not require chemical digestion such as: – vitamins, free amino acids, minerals, cholesterol, and water 25-5
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Digestive Function • digestive system – the organ system that processes food, extracts nutrients from it, and eliminates the residue • five stages of digestion – ingestion - selective intake of food – digestion – mechanical and chemical breakdown of food into a form usable by the body – absorption - _____________________ into the epithelial cells of the digestive tract and then into the blood and lymph – compaction - absorbing water and consolidating the indigestible residue into feces – defecation - elimination of feces
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25-6
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General Anatomy • Like earthworms, we are basically tubes. The hollow center of the tube is considered to be “outside the body” • Food that is ingested and is then defecated ___________________ ___________________________... it just passed through • Only nutrients that are absorbed by the alimentary canal and transferred to the bloodstream have “entered the body” 25-7
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Digestive system organization • digestive system has two anatomical subdivisions • alimentary canal
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