From Mouth to Anus
The Digestive System
Challenges
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Food Presents all animals with at least two
challenges:
1.
2.
How to obtain it?
How to break food down into small molecules that
can be passed to cells that need them?
Function

To help convert foods into simple molecules
that can be absorbed and used by the cells of the
body.
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The digestive system is built around an alimentary
canal  a one-way tube that passes through the
body.
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This is also known as the Gastro Intestinal Tract (G.I.
Tract)
Anatomy and Physiology of the G.I. Tract
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Mouth (oral cavity): place where food enters;
mechanical and chemical digestion begins
Tongue: moves food around, pushes it to back
of the mouth for swallowing, clump of food is
then called a bolus.
Teeth (mechanical): breaks down food into
smaller particles to increase surface area for
chemical digestion
A & P of G.I. Tract

Salivary Glands (chemical): secretes saliva, which
contains an enzyme called amylase. Salivary
amylase breaks down starch into disaccharides.
A & P of the G. I. Tract
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Esophagus: muscular tube that connects the
mouth to the stomach
Peristalsis: wave-like motion that pushes food
down
A & P of G.I. Tract
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Stomach:
HCl and pepsin break
down proteins.
Lined with mucus so that
it doesn’t digest itself
Stomach muscles
contract to mix food into
chyme.
Food stays here 2-4
hours
A & P of G.I. Tract
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Small Intestine: approx. 6 meters long
Made of three sections: duodenum, jejunum,
ileum
Most important digestive organ, as digestion of
carbs, fats, and proteins is completed here.
Also the site of nutrient absorption (villi and
capillaries)
A & P of G.I. Tract
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Large intestine a.k.a. “COLON”
Approx. 1.5 meters long
Site of water absorption
Leaves behind solid material called feces
Food stays here 18-24 hours
Not enough water absorbed= diarrhea
Too much water absorbed= constipation
A & P of G.I. Tract

Rectum: stores solid waste until appropriate
time for removal
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Anus: solid waste exits through this opening
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Entire journey takes approx. 24-33 hours
ACCESSORY TO DIGESTION

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These structures are
NOT a part of the G.I.
Tract, food does NOT
travel here!
LIVER: produces bile,
which helps break down
fats
GALLBLADDER:
stores bile
Accessory to Digestion
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CBD: common bile duct,
transfers digestive juices
from liver, pancreas, and
gallbladder to the small
intestine
Pancreas: secretes fluid
to help breakdown fats,
carb’s, and proteins in
the small intestine.
Digestive System Anatomy
Quiz

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1. Where does digestion
begin?
2. What is the name of
the tube that connects
the mouth to the
stomach?
3. What enzyme does
your salivary glands
secrete?
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4. What is the name of
the wave-like motion
that pushes food
throughout the G.I.
Tract?
5. In which organ does
nutrient absorption take
place?
6. In which organ does
water absorption take
place?
QUIZ
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7. Trace the pathway a
hamburger will travel,
from the mouth to the
anus. Hint: You should
include 7 structures.
8. What is the function
of the liver?
9. In which organ do the
digestive juices work in?
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10. What organic
compound does your
stomach start breaking
down?
11. Where are
carbohydrates broken
down? Careful!
12. How do nutrients
get from the small
intestine to the
bloodstream?
ANSWERS
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1. Mouth
2. Esophagus
3. Amylase
4. Peristalsis
5. Small intestine
6. Large intestine
7. Mouth esophagus
stomach s.intestine
l.intestinerectum
anus
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8. Produce bile
9. Small intestine
10. Proteins
11. Mouth and small
intestine
12. Villi, capillaries