Carbohydrates
Proteins
Lipids
Where the
nutrient is
digested.
Carbs’ digestion begins in the
mouth. However, most of it is
digested in the duodenum.
Lipid digestion occurs in
the SI.
The enzymes
involved.
Salivary amylase, pancreatic
amylase, brush border
enzymes, maltase, sucrose, and
lactase.
How the
nutrient is
absorbed.
Carbohydrates are broken
down into maltose, amltriose,
and short oligosacchradies and
other disaccharides. These
molecules are hydrolyzed to
their monosaccharides by
brush border enzymes on the
microvilli of the epithelial cells
in the SI. Monosaccharides are
moved across the epithelial cell
membrane by secondary active
transport. Then glucose leaves
the epithelial cells by facilitate
diffusion and enters the
interstitial fluid. It then diffuses
into nearby blood capillaries
within the intestinal villi.
Protein digestion
begins in the stomach.
In the SI, polypeptides
are broken down into
free amino acids,
dipeptides, and
tripeptides.
Endopeptidases
(trypsin, chymotrypsin,
elastase),
exopeptidases
(carboxypeptidase,
aminopeptidase),
pancreatic lipase, and
pepsin.
In the SI, where all
larger peptides are
broken down into
amino acids, amino
acids are cotransported
with Na+ into epithelial
cells and then secreted
into blood capillaries.
Di- and tripeptides are
also carried into
epithelial cells where
they are hydrolyzed
into free amino acids
and then also secreted
into blood capillaries.
Pancreatic lipase,
phospholipase A.
Fat is emulsified by bile
salt micelles. The
products of fat digestion
(free fatty acids,
monglycerides and
lysolecithin) dissolve in
the micelles to produce
mixed micelles. Then the
products leave the
micelles and enter
epithelial cells. Here,
they are resynthesized
into triglycerides and
phospholipids. These
combine with protein to
form chylomicrons.
These are secreted into
central lacteals of SI villi,
which goes to the
thoracic duct and
eventually to the blood
stream.
How the body
uses the
molecule.
The glucose is absorbed from
the intestines into the blood
and transported to the liver,
muscles, and other sites where
it is converted to another
glucose polymer, glycogen, and
stored. Glycogen helps
maintain the proper amount of
glucose in the blood by
removing and storing excess
glucose derived from ingested
food or by supplying it to the
blood when it is needed by the
body cells for energy.
(http://www.diet-andhealth.net/Nutrients/carbohyd
rates.html)
Antibodies defend
the body from germs.
Contractile proteins
are responsible for
movement in muscle
fibers.
Enzymes speed up
chemical reactions.
Storage proteins
store amino acids.
Some are used as
hormones, some as
transporters, some as
structural support
(elastin, collagen,
keratin).
The body uses lipids to
store energy fuel,
insulate body tissues,
cushion and protect
organs, produce ketone
bodies - the primary
energy source for the
heart and brain, and as
cell membranes
(phospholipid
membrane).
(http://wiki.answers.co
m/Q/How_does_the_b
ody_use_lipids_or_fats)