Download digestion part 3.pptx

The Small Intestine and Digestion
Q: Breaking down of carbohydrates (sugar) begins
where?
–  in your mouth (enzyme: salivary amylase in saliva)
Q: Breaking down of proteins begins where?
–  in your stomach (enzyme: pepsin)
•  but, resulting molecules are still too large for
your cells to absorb and use!!!
•  so, proteins, fats and sugars must be further
mechanically and chemically digested in your
small intestine
4) Small intestine:
a tube 2.5 cm in diameter and 4-6 m long!
mouth
esophagus
stomach
small intestine
large intestine
The Small Intestine (SI)
•  The small intestine is
attached to the
stomach and is
divided into three
sections:
1) The duodenum
(connected to the
stomach)
2) The jejunum (middle
portion)
3) The ileum (connected
to the large intestine)
5) Liver (organ):
-  Is the largest organ in
the human body
-  Produces 1L of bile
each day
Bile
-  Green fluid produced
by the liver and stored
in the gall bladder
-  Breaks up (emulsifies)
fat particles in the SI
6) Gall bladder (organ)
- Stores bile and
releases it into the
duodenum (SI) when
necessary
7) Pancreas (organ):
- Secretes 1.3 L of pancreatic juices
into the SI each day
- Secretes insulin (hormone that
breaks down sugar)
Digestion of Food in the SI
• 
When food enters the small intestine
three substances are secreted into it:
1) Bile secreted by the gall bladder (but
produced in the liver)
Bile aids in the mechanical digestion of fats.
2) Intestinal juices secreted by glands that line
the walls of the small intestine
3) Pancreatic juices secreted by the pancreas
These 2 juices contain enzymes that
complete the chemical digestion of
carbohydrates, proteins and fats in the SI
Mechanical Digestion in the SI
•  Food is also churned in the SI just like in
the stomach
–  This is necessary to mix the chyme with the
digestive juices of the SI
•  Food advances throughout the SI through
peristalsis just like in the esophagus
Digestion of Fat in the SI
•  The chyme that leaves your stomach and enters
the SI contains water and fat.
•  Water and fat do not mix, they coalesce
–  This means the fat floats to the surface of the water
•  Bile is required to separate the fat molecules
from the water molecules.
–  This is called emulsification
•  Emulsified fat molecules have only been
mechanically digested as bile does not contain
enzymes and only separates molecules from
each other.
•  Emulsified fat molecules then mix with digestive
juices (in the SI) containing enzymes which
digest the fat chemically.
Practice Questions
1)  What are the names of the 3 sections of the small
intestine?
2)  How is the inner lining of the small intestine special
and why is this important to digestion?
3)  What three substances does the small intestine
contain and which organs or cells are responsible for
secreting each of these substances?
4)  What 3 nutrients are digested in the small intestine and
what are the names of their individual components?
5)  What is the function of bile, where is it produced and
where is it stored?
6)  What hormone does the pancreas produce?
7)  What process does the stomach and the small
intestine have in common? What about the esophagus
and the small intestine?