Download Carbohydrate Digestion

Animation: Carbohydrate Digestion
Your cells use glucose, a form of carbohydrate, for energy. The primary goal of
carbohydrate digestion is to break down the larger, more complex molecules
found in food, known as polysaccharides, into monosaccharides that can be
absorbed and converted into the glucose and other simple sugars our bodies
require. It takes from one to four hours for all the carbohydrate in the sandwich
to be broken down, absorbed, and circulated to the cells as glucose.
Carbohydrate digestion begins in the mouth with mechanical and chemical
processes. The food is shredded and crushed by the teeth and mixed with saliva.
The enzyme salivary amylase in our saliva begins to hydrolyze starch or
polysaccharides to form shorter strands and the disaccharide maltose. Now
referred to as a bolus, the food leaves the mouth and travels through the
esophagus and enters the stomach. Mechanical digestion continues with
peristalsis which is the rhythmic contraction of the smooth muscles that moves
the bolus through the digestive tract. Chemical digestion continues when the
bolus mixes with the hydrochloric acid and protein-digesting enzymes in the
gastric juices. These gastric juices inactivate salivary amylase, halting further
digestion of starch in the stomach. Fiber continues to be churned and softened,
slowing the gastric emptying and producing a feeling of fullness.
The majority of carbohydrate digestion is accomplished in the small intestine. As
chyme enters the duodenum, the pancreas is stimulated to secrete amylase
which mixes with the chyme and hydrolyzes any remaining starch into maltose.
The final step in carbohydrate digestion is completed on the surface of the small
intestine where specific enzymes break down disaccharides into
monosaccharides. The monosaccharides formed are absorbed through the
microvilli and then into the capillaries.
Fiber is a component of whole grains that is not digested by the human intestinal
tract. While it is not digested, its action promotes a healthy intestinal tract. The
fiber passes through the small intestine undigested and enters the colon, also
known as the large intestine. Once inside, the bacteria break down the fiber,
producing gas and a few short-chain fatty acids. The remaining fiber in the colon
is excreted in the feces. What began as a sandwich has now been broken down
into monosaccharides that can be absorbed into the blood to be used by the cells
of the body.