DIGESTION OF CARBOHYDRATES,
PROTEIN and FAT
Marisa Laursen
2/10/04
CARBOHYDRATES
AKA: complex carbohydrates, starches, polysaccharides
End products of digestion: monosaccharides (glucose, galactose, fructose). Glucose is the
main energy-supplying food for cellular activity.
•
Mouth: Digestion begins in the saliva in the mouth. The enzyme amylase, contained
within the saliva (produced by the parotid gland), breaks down the starch to smaller
compounds called dissacharides (maltose and isomaltose).
•
Stomach: The enzyme amylase continues to act on the food for several hours, lowers
the pH below 4.0.
•
Small Intestine: Pancreatic amylase (produced by the pancreas), along with other
enzymes produced by the small intestine (maltase, isomaltase, lactase, sucrase),
convert the dissacharides into monosaccharides (glucose, fructose and galactose)
which can easily be absorbed. These simple sugars enter circulation.
•
Liver: In the liver, the fructose and galactose are converted to glucose.
polysasaccharides
dissacharides
monosaccharides
PROTEIN
The end product of digestion: amino acids
•
Stomach: Digestion begins in the stomach. The enzyme pepsin breaks large protein
chains (strings of amino acids) into smaller chains called proteoses, peptones, and
polypeptides.
o
Pepsin relies on hydrochloric acid (HCL) to activate it. As HCL is
secreted, the pH of the stomach drops. At a pH of approx. 2, the pepsin
becomes fully active.
•
Small Intestine:
o
Pancreas: Secretes enzymes (trypsin, chymotrypsin and
carboxypolypeptidase) into small intestine. These enzymes act on the small
chain proteins.
o
Additional enzymes are secreted by the small intestines.
o
The small chain proteins are converted into amino acids.
large amino acid chain
small amino acid chain
individual amino acids
FAT
AKA: triglycerides
End products of digestion: fatty acids and glycerol
•
Small Intestine: Digestion of fat mainly occurs in the small intestine.
o
Liver produces bile salts, stores it in gall bladder. These bile salts are
secreted into small intestine, where they emulsify and break up fat into
small fat globules. These globules are still triglycerides (no chemical
change has occurred yet, as bile is not an enzyme). The purpose of the
bile is to increase the surface area of the fat.
o
The pancreas secretes the enzyme lipase into the small intestine. Lipase
transforms the triglycerides into fatty acids and glycerol.
triglycerides
small fat globules
fatty acids and glycerol
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