Digestive System

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• Digestive System

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Figure 41.13 The human digestive system
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• Digestion begins in the oral cavity (mouth).
• Saliva begins the chemical digestion of food.
  Saliva contains the protein _________ to
  lubricate the food for swallowing.
• ___________breaks down starch and glycogen.
• Food is shaped into a ball (bolus) and is then
  swallowed.

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• The food then proceeds down through the esophagus
  through an involuntary
  contraction of smooth muscle tissue.

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Pharynx (throat)

• Is where the esophagus and the windpipe meet.
• When food is swallowed, the closes
  the passage to the windpipe.
• The epiglottis is a flap made of cartilage that
  cover the glottis (opening to the windpipe).

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Esophagus

• Conducts food from the pharynx to the stomach.
• The mouth, pharynx and esophagus are responsible
  for carbohydrate digestion.

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Stomach

• The opening to the esophagus is called the
  cardiac sphincter.
• The opening end of the stomach to the small
  intestine is called the pyloric sphincter.
• The stomach produces______________.
• If the cardiac sphincter opens when it shouldnt,
  you get acid reflux or heartburn.

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Gastric Juice

• Has a pH of
• Contains ____________ that breaks down proteins.
• A coating of mucus helps protect the stomach
  wall.
• The stomach epithelium must be regenerated every
  3 days.
• Ulcers are generated when the stomach wall is
  being degraded.

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• After chemical digestion in the stomach, the food
  has been turned into a nutrient broth called
  _________.
• It takes 2 to 6 hours for the stomach to empty.

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Small intestine

• After leaving the stomach, food enters the small
  intestine (SI).
• The SI is the major organ of digestion and
  absorption.
• The first part of the SI is called the
  ______________________.

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• In the duodenum, chyme form the stomach mixes
  with digestive juices from the pancreas, liver
  and gallbladder.

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Figure 41.16 The duodenum
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Pancreas

• Produces hydrolytic enzymes and an alkaline
  solution made of bicarbonate.
• The __________________acts as a buffer to help
  neutralize the acidic chyme.

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Liver

• In digestion, the liver produces ________.
• Bile contains no digestive enzymes, but contains
  salts which acts as a detergent and helps in the
  absorption of fats.
• Bile also contains some wastes of the liver (red
  blood cell destruction).

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Small intestine

• Continues the digestion of proteins.
• Produces trypsin, and some peptidases.
• Proteins are broken down into single amino acids
  here.

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SI

• Produces _______________ to digest DNA and RNA.
• These nucleic acids are broken down into single
  nucleotides.

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SI

• Breaks down and absorbs fats with the help of
  bile from the liver.
• Nearly all fate that enters the SI is completely
  undigested.
• The SI also produces ____________ to aid in lipid
  digestion.

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SI

• The __________ and jejunum are located near the
  end of the small intestine.
• They aid in the absorption of nutrients and
  water.
• The SI has many finger-like projections for
  absorption called villi and microvilli.

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Large Intestine (LI)

• Is also called the ___________.
• It is connected to the SI with a sphincter.
• The cecum is the pouch located in the LI near the
  SI.
• The appendix is a finger-like extension of the
  cecum.

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LI

• The primary job of the LI is to reabsorb water.
• Together, the SI and the LI reabsorb 90 of the
  water that was used for digestion.
• Wastes become more solid as they move through the
  LI through peristalsis and results in feces.

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LI

• The end of the LI (colon) is called the rectum.
• Between the rectum and the anus there are 2
  sphincters one involuntary and the other
  voluntary.

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Vertebrate Digestive Systems

• Vary depending on the diet of the organism.
• The oral cavity contains incisors, canines and
  molar teeth.
• The law is designed for the diet.
• Herbivores have a very long cecum and LI.
• Carnivores and omnivores have a small cecum and a
  shorter LI.

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Figure 41.21 The digestive tracts of a carnivore
(coyote) and a herbivore (koala) compared
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Crop

• Birds have a ___________, which is an esophageal
  pouch.
• The pouch houses symbiotic bacteria to aid the
  organism in digestion.