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Digestion
Absorption and Transport
• Digestion
the process of breaking down food into its
basic components so they can be
absorbed
• CHO, fat, pro are hydrolysed
• Vits, mins, water aren’t
(Chapter 3)
Digestion
Your GI tract
is like a tube!
Food travels through the lumen while it gets digested
Digestion
• Two types of action:
• Mechanical
• Chemical
1
Peristalsis
Sphincters: open and close
2
GI Tract Signals
• Food, pH, nerves, hormones
• Enterogastrones:
• Gastrin
• CCK
• Secretin
Segmentation
Accessory Organs
Emulsification of Fat by Bile
Absorption
• Taking up nutrients from lumen into
the cells

3
Absorption
• The huge surface area of the small
intestine facilitates nutrient
absorption
• Folds, Villi, and Microvilli
• (Oh my!)
Absorption
• Nutrients can be absorbed through
simple diffusion, facilitated diffusion,
or active transport.
Carrier loads
nutrient on
outside of cell . . .
Outside
cell
Carrier loads
nutrient on
outside of cell . . .
Cell
membrane
Inside
cell
. . . and then
releases it on
inside of cell.
SIMPLE
DIFFUSION
Some nutrients (such
as water and small
lipids) are absorbed by
simple diffusion. They
cross into intestinal
cells freely.
FACILITATED
DIFFUSION
Some nutrients (such as the watersoluble vitamins) are absorbed by
facilitated diffusion. They need a
specific carrier to transport them
from one side of the cell
membrane to the other.
(Alternatively, facilitated diffusion
may occur when the carrier
changes the cell membrane in
such a way that the nutrients can
pass through.)
. . . and then
releases it on
inside of cell.
ACTIVE
TRANSPORT
Some nutrients (such as
glucose and amino acids)
must be absorbed actively.
These nutrients move
against a concentration
gradient, which requires
energy.
Stepped Art
Fig. 3-9, p. 81
4
Transverse
colon
Opening from
small intestine
to large intestine
Ascending
colon
End of
small
intestine
Descending
colon
Appendix
Rectum
Anus
Sigmoid
colon
Stepped Art
Fig. 3-7, p. 78
Where’s the Fiber?
• Undigested residues, including some
fibers, continue through the
digestive tract and form stool.
Gastrointestinal Bacteria
A healthy GI tract has many
different non-disease-causing
bacteria known as flora or microflora.
BTW
“Food combining” which emphasizes
separating food for digestive
purposes is a myth!
• Probiotics are bacteria found in the
GI tract that can be beneficial to
health.
• Prebiotics are foods (e.g. fiber) that
are used as food by intestinal
bacteria.
• Bacteria produce vitamins!
5
Next step: Transport
• Once nutrients cross into the villi,
they are transported to the rest of
the body
• Through blood and lymph systems
Preparing for Transport
Water-soluble nutrients and small
products of fat digestion are released
to the bloodstream. First stop is
liver.
Fat-soluble vitamins and larger fats
form chylomicrons before being
released to the lymphatic system.
Then via thoracic duct to blood.
Common Digestive
Problems
6
Heartburn and
“Acid Indigestion”
Belching and Gas
• Strategies
•
•
•
•
Eat slowly.
Chew thoroughly.
Relax while eating.
Watch bothersome foods.
• Gastroesophageal reflux (GERD) is
the backward flow of stomach
contents into the esophagus.
• Antacids and acid controllers may
help indigestion.
• Hiccups are triggered by eating or
drinking too fast.
Heartburn and
“Acid Indigestion”
• Strategies
•
•
•
•
•
•
•
•
•
Ulcers
• Peptic ulcers can be gastric or
duodenal.
• Strategies
• Take prescribed medicine.
• Avoid caffeine- and alcoholcontaining foods.
• Minimize aspirin and ibuprofen use.
• No smoking.
Small meals
Liquids in-between meals
Sit up while eating.
Wait 1 hour after eating before lying down.
Wait 2 hours after eating before exercising.
Refrain from tight-fitting clothing.
Avoid bothersome foods.
Refrain from tobacco use.
Lose weight if overweight.
Diarrhea
• Frequent, loose, watery stools
• Strategies
•
•
•
•
Rest
Drink fluids
BRAT diet
Medical help is needed if it persists.
7
Constipation
Possible complications:
• Hemorrhoids
• Diverticulosis is a condition in which
the intestinal walls weaken and
bulge. The bulging pockets are
called diverticula.
• Diverticulitis is when they are
inflammed and requires intervention.
Constipation
• Prevention Strategies
•
•
•
•
High-fiber diet
Increased fluids
Exercise regularly.
Respond quickly to the urge to
defecate.
8