Carbohydrate Digestion...

Definition

The Digestion of Carbohydrate consumed by humans

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Causes, incidence, and risk factors

One of the primary goals of the digestive process is to provide every body cell with sufficient amounts of energy to sustain itself and remain alive. Many of the vital chemical reactions that take place in the cell require energy, which is derived from the oxidation of the glucose, within the cell. Glucose is carried to the cell as the end product of carbohydrate metabolism.

There, in the presence of enzymes and oxygen, the glucose is converted into carbon dioxide, water and energy. The carbon dioxide and water are non-essential by-products of this reaction; the important product is the heat energy, which is derived from the glucose.

glucose + oxygen = carbon dioxide + water + heat

(enzyme) (energy)

The oxygen used in this chemical reaction is brought from the lungs to the cells by the red blood cells, containing hemoglobin. The hemoglobin and oxygen combine chemically until enzymes in the cell separate them for the oxidation process. Glucose is one of literally hundreds of chemical compounds called carbohydrates or saccharides. The molecules of all carbohydrates are made up of building blocks called simple sugars. Carbohydrates may be subdivided into three groups:

Monosaccharides, like glucose, consist of a single sugar building block.

Disaccharides, like common table sugar (sucrose) consist of two simple sugar building blocks.

Polysaccharides, like starch and cellulose, consist of many simple sugar building blocks joined together in a long line in daisy-chain fashion.

It appears that the only carbohydrate of any chemical value to the body is the simple sugar or monosaccharide called glucose. Therefore, one of the major goals of the digestive process is to extract the glucose from the various carbohydrates that we ingest every day. Carbohydrate sources are primarily starches (like grains) and sugars (like cane sugar, milk sugar, fruit sugar). The enzyme ptyalin or amylase in the saliva begins to break down the food in the mouth. Food does not stay in the mouth long enough for ptyalin to complete the breakdown of starches. Yet the action of ptyalin continues for several hours after food has entered the stomach...until the food is mixed with the stomach secretions. Once the pH of the food's environment falls below approximately 4.0, as will occur in the second portion of the stomach, this enzyme becomes nonactive. But, before this happens, 30 to 40 percent of the starches will have been changed into maltose and isomaltose. They are now ready to enter the small intestine as part of the chyme. When muscle tone and other factors are normal, the result is a beautifully timed and regulated pumping. With each strong wave of movement, several milliliters of chyme are forced from the stomach into the duodenum. This stomach and intestinal reflex is especially sensitive to the presence of irritants, breakdown products of protein digestion, proper concentration of fluid and to substances too acid or too alkaline.

As covered previously, this emphasizes the need for sufficient hydrochloric acid and other gastric secretions, the importance of drinking water before eating and the avoidance of antacids or other drugs that would interfere with or halt digestion. As much as 30 to 40 percent of starches have been changed (broken down) into maltose and isomaltose (combinations of simple sugars) before reaching the small intestine. After the chyme enters the duodenum and mixes with pancreatic juice, starches, not yet split, are immediately digested by amylase. Like saliva, pancreatic secretions contains large amounts of amylase, acting identically to the amylase in saliva, splitting the starches into maltose and isomaltose. Carbohydrate, split down into simple sugar combinations (disaccharides), lactose, sucrose, maltose and isomaltose, are then split even further into just simple sugars (monosaccharides) by enzymes from the cells lining the small intestine. These simple sugars (galactose, glucose, fructose) are then absorbed into portal blood...that is, on their way to the liver. About 80 percent of the final products of carbohydrate digestion is glucose. Blood sugar is glucose.

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