Digestive System

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Digestive System
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Digestion - breaking down food into small
molecules that can be passed into your cells.
Includes all organs below

Section 38-2

• Alimentary Canal - a one-way tube that passes
  through the body.
• (mouth, pharynx, stomach, small intestine, large
  intestine.)
• Accessory structures -do not carry food, but aid
  in digestion.(salivary glands, pancreas, liver)

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• 1. The Mouth
• Teeth - tear/crush food
• Mechanical digestion - physical breakdown of
  food
• Chemical digestion - enzymes break food into
  smaller food molecules. Exstarch into glucose
• Saliva - moistens food
• Enzyme salivary amylase - breaks down starches
  into simple sugars
• Food passes through throat past the epiglottis
• Q Do enzymes get used up in these chemical
  reactions?
• A No.
• Q What is their optimal temperature and pH?
• A In humans, 98.6 degrees, and neutral to
  slightly basic, except for stomach enzymes.

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• 2. The Esophagus
• Muscular tube connecting pharynx to stomach
• Moves through peristalsis rhythmic waves of
  muscular contractions
• Squeezes food ball along esophagus
• Can swallow even when standing on your head!
• Can begin in absence of food lump in your
  throat.
• Food bolus enters stomach through a sphincter
  (ring of muscle)
• When sphincter fails to close, acidic gastric
  juice may splash up into esophagus heartburn.

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• 3. The Stomach-
• Football shaped, holds 1 liter
• Mechanical - smooth muscles churn and mix food
• Lining of stomach produces mucus-lubricates/protec
  ts stomach wall
• Chemical - lining contains gastric glands which
  produce
• HCl - kills bacteria,activates pepsin
• Enzyme Pepsin - breaks proteins into smaller
  polypeptides/amino acids.
• Enzyme Rennin -curdles milk protein
• Final pH of gastric contents 2.
• Chyme - mixture that stomach produces
• 1-2 hours - out pyloric sphincter valve
• (Water, salts, alcohol, some drugs - can be
  absorbed through stomach)
• Peptic Ulcer - stomach lining is digested/hole in
  wall. Most caused by a bacteria,cured with
  antibiotics.

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Helicobactor pylori Bacteria causing stomach ulcer
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• 4. The Small Intestine - 6 m long x 3 cm wide
• Chyme enters the duodenum - (1st of 3 parts of
  small intestine.) Enzymes enter here from
• Liver - makes bile which emulsifies fats (breaks
  into small droplets).
• Gall Bladder - stores bile
• QWhat are gall stones?
  
• Q Can you live without your gallbladder?
• Pancreas - makes 3 enzymes
• Pancreatic Amylase - breaks starch into simple
  sugars
• Trypsin - breaks proteins into A.A.
• Lipase - breaks fats into fatty acids glycerol
• Small Intestine enzymes
• Maltase, sucrase, lactase - breaks down sugars
  (disaccharides) into simple sugars
  (monosaccharides)
• Peptidase - breaks down proteins into A.A.
• Q Can you live without your liver or pancreas?

Click to enlarge diagram
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A Close-up Substances entering the Duodenum
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 The Liver and the Pancreas
Section 38-2
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• Absorption in the Small Intestine
• After duodenum Jejunum and Ileum (total 6 meters
  long)
• Here are villi - fingerlike projections covered
  with microvilli.
• These folds and projections provide large surface
  area for absorption of nutrients.
• If the lining were completely unfolded and spread
  out, it would be the size of a tennis court!
• Carbs and Proteins - go from villi to capillaries
  to cells
• Fats - go from villi to lymph vessels to cells
• Now all that is left is water, cellulose, other
  undigestible substances.

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 The Small Intestine
Section 38-2
Small Intestine
Villus
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Villi and Microvilli in the Small Intestine
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• 5. The Large Intestine/Colon -
• These substances pass into appendix, a small
  saclike organ
• Clogged and inflamed appendicitis. Removal
  needed.
• Large Intestine -11.5 long x 5 cm wide - removes
  water from undigested material
• Bacteria in colon produce needed compounds,
  including Vitamin K.
• Antibiotics can destroy these beneficial
  bacteria. (Eat yogurt!)
• Next - eliminate wastes. Go out rectum and anus
  feces
• Disorders
• Diarrhea - not enough water is absorbed.
• Constipation - too much water is absorbed - stays
  in colon too long.(Eat fiber!)
• Colon polyps or cancer

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Review Can you trace this apple through the
digestive system, naming each organ and enzymes
involved?
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Up Next Now that we have digested, how do we
excrete our liquid wastes?