completely breaks it down to disaccharide (maltose and isomaltose). Sucrose, maltase,
isomaltase, and lactase finally break down this disaccharide, along with other
disaccharides ingested in foods (sucrose, lactose) to the monosaccharides glucose,
fructose, and galactose. These simple sugars are the end products of carbohydrate
digestion and are absorbed through the intestinal mucosa into the bloodstream via a
carrier-mediated transport system. They can be either oxidized immediately by the cells
to do work or they can be stored until they are needed by the body. They can be stored
in two ways:
Synthesized to glycogen in the liver, or
Synthesized to fat and stored in fat cells.
1-19. THE DIGESTION OF FAT
a. There is virtually no fat digestion in the mouth or stomach. The first step in
the digestion of fats is emulsification, the physical break up of fat globules into small
droplets. This occurs in the small Intestine by the action of bile and bile salts.
Emulsification permits the digestive enzymes (lipases) to act upon the fat molecules and
break them down into monoglycerides, fatty acids, and glycerol, the end products of fat
digestion and the form in which they are absorbed through the intestinal mucosa.
b. The absorption occurs through a rather complex and poorly understood
mechanism. The end products of lipid digestion can be either oxidized by the cells or
transformed into glucose that, in turn, is then oxidized by the cells to do work. They
may also be stored as fat.
1-20. THE DIGESTION OF PROTEINS
The digestive process of proteins begins in the stomach. In the stomach, pepsin,
an enzyme activated by the low pH of the stomach, breaks apart long chain
polypeptides and proteins into simpler short-chain peptides referred to as proteoses and
peptones. Further hydrolysis of these fragments to dipeptides and amino acids is
accomplished in the small intestine by the enzymes chymotrypsin and trypsin.
Ultimately, all peptide fragments are broken down to their constituent amino acids, the
end products of protein digestion, by various carboxypeptidases and aminopeptidases
present all along the walls of the small intestine. The mechanism by which the amino
acids are absorbed across the small intestine walls is poorly understood.
Section IX. DISORDERS AND DISEASES OF THE DIGESTIVE TRACT
There are several common disorders of the digestive system. Many of these
disorders can be treated by drugs that you will dispense in the pharmacy.