Figure 41.13 The human digestive system

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DIGESTION the breakdown of food into simpler
substances by the body or by a cell.
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(No Transcript)
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Intracellular Digestion in Paramecium
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Paramecium
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Extracellular Digestion in a Gastrovascular Cavity
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Alimentary Canals (complete digestive tracts)
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The Human Digestive System
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Digestive System
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• MOUTH
• Taste Buds
• Salivary Glands
• Amylase digests starches

PHARYNX at the back of the mouth leads to the
esophagus and trachea
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Adult Mouth
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From Mouth to Stomach the Swallowing Reflex and
Esophageal Peristalsis
Cardiac sphincter
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• ESOPHAGUS -about 25 cm/1 ft
• peristalsis occurs within to move bolus of
  food
• cardiac sphincter at the end
• STOMACH
• hydrochloric acid breaks down
• food (in gastric juice)
• pepsin digests protein
• mucus lining protects
• churning of food makes chyme

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The Duodenum (Active Hormones)
Enterogastrone
Cardiac sphincter
pyloric sphincter
Gastrin

• Secretin

CCK
Secretes NaHCO3, pancreatic juices that digest
macromolecules
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Homeostatic Regulation of Cellular Fuel
Pancreas
Pancreas
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Secretion of Gastric Juice
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Anatomy and Histology of the Stomach
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Enzymatic Digestion in the Human Digestive System
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• SMALL INTESTINE
• about 23 feet long in adults
• pancreas secretes pancreatic
• fluid (contains NaHCO3)
• amylases break down starches
• proteases break down proteins
• lipases break down fats

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Activation of Protein-Digesting Enzymes in the
Small Intestine (secreted by pancreas)
These proteases cleave bonds adjacent to certain
amino acids
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The Structure of the Small Intestine
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• SMALL INTESTINE (cont)
• Liver makes bile to break
• down fats it is stored by the
• gall bladder it is what gives
• solid waste its color
• villi loaded with blood vessels

Howdy Ho!

• LARGE INTESTINE/COLON
• about 3m/9 ft in adults
• removes water from waste
• waste moves to rectum where it is held before
  excretion at the anus

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Large Intestine (Colon)
goblet cells
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The Digestive Tracts of a Carnivore (coyote) and
a Herbivore (koala) Compared
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• Polyps are small growths arising from the
  epithelial lining that may be benign or
  cancerous.
• Diarrhea and constipation are two common
  complaints of the large intestine.
• Causes of diarrhea include infection of the lower
  tract and nervous stimulation, both moving feces
  more rapidly than normal, but also causing
  dehydration if prolonged.

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Ruminant Digestion
(removes water)
(Boluses enter microbes break down)
(boluses enter and microbes break down)
(enzymatic digestion)
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List the following in the order in which food
would move in the digestive process esophagus,
small intestine, stomach, large intestine,
mouth, pharynx, cardiac sphincter.
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What activates pepsin in the stomach? Ulcers
are caused by . . .
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• List three substances involved in food digestion
  and
• from where they are released ex amylases from
  pancreas
• their target ex. duodenum
• what they do ex digest carbs

Compare the function of the small intestine to
the large intestine.
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The main function of the large intestine is to.
. . What is the cecum? The friendly bacteria
in large intestine function to. .
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Food is prevented from entering the trachea
because it is blocked by the Muscular
contractions called ________ occur when muscles
in the esophagus squeeze the food as it pass
through it.
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Compare the function of the small intestine to
the large intestine.