The Digestive System

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The Digestive System
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• Purpose of digestive system
• Converts food into small molecules that can be
  used by cells!!
• Why do the food molecules need to be small??
• Four phases
• Ingestion?digestion? absorption? elimination

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• Ingestion process of putting food into your
  mouth
• Digestion process of breaking food down
• Mechanical physical breakdown of large pieces
  increases surface area
• Chemical enzymes are used to break food into
  smaller molecules

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• Absorption small molecules absorbed by cells in
  small intestine
• Elimination removal of undigestable materials
  (like cellulose)

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Mechanical vs Chemical

• Mechanical grinding, tearing, peristalsis
  (churning action).increases surface area for
  enzyme action
• Chemical enzymes work to make larger molecules
  into smaller molecules (ex starch--gtsimple
  sugars)

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Your mouth does both!

• http//www.hns.org.uk/bio/index.php?optioncom_con
  tentviewarticleid123Itemid176

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• Mechanical digestion is accomplished by chewing
• Your teeth cut, tear, grind, and crush food
• Your tongue moves the food around so the tongue
  can work on it

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• Chemical digestion of mouth
• Enzymeamylase
• Amylase begins to break down long starches
  forming sugars
• Saliva also has lysozyme.an enzyme that protects
  us against bacteria

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• When you swallow the epiglottis covers the
  windpipe so that you dont choke!

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Esophagus

• Tube connecting throat to stomach
• Peristalsis rhythmic contractions of smooth
  muscles that move food through the digestive
  system

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Stomach
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• Large muscular sac
• Gastric glands release pepsin and HCl
• Chemical digestion
• Proteins--gt smaller polypeptide chains

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• Another gland produces ______mucus_____________
• o This lubricates so food can pass easier and
  protects the stomach wall
• o If acids erode the stomach wall and create a
  sore it is called a peptic ulcer
• o Now scientists know peptic ulcers caused by
  Helicobacter pylori

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• Mechanical digestion smooth muscle churns and
  mixes food
• Chyme mixture with an oatmeal-like consistency

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Small Intestine

• Most digestion and all absorption
• First part of SI duodenum
• Mixes with fluids from the pancreas, the liver
  and the lining of the SI

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• Pancreas produces enzymes that break down
  carbohydrates, proteins, lipids and nucleic acids
• Also produces sodium bicarbonateto neutralize
  stomach acid

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• Liver and Gallbladder..help in the digestion of
  fats!
• Bile emulsifies fats
• Bile is made in the liver and stored
• (released) in the gallbladder

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Absorption also occurs in SI

• Structure adapted for this function!
• Villi fingerlike projections
• Microvillitiny projections covering villi

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Large Intestine

• Absorbs water from undigested material
• Bacteria found here help to produce Vitamin K
• Concentrated waste material feces
• Too much water absorbed constipation
• If not enough water is absorbed diarrhea

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