Digestion and Absorption of Carbohydrates
From Mouth to Stomach
The digestion of carbohydrates starts from eating the foods as the chemical and mechanical digestion of carbohydrates begins in the mouth.
The Chewing Process crumbles the carbohydrate foods into smaller pieces. The saliva secreted from the salivary glands coats the food to facilitate absorption.
About five percent of starches in foods are broken down in the mouth with the aid of amylase enzyme in saliva. No further chemical breakdown of starches occurs once carbohydrates reach the stomach because the amylase enzyme in saliva does not function in the acidic conditions of the stomach. However, the mechanical breakdown of starches continues as the powerful peristaltic contractions of the stomach mix the food into a more uniform mixture called chyme.
From Stomach to Small Intestine
From the stomach, the chyme is gradually expelled into the upper part of the small intestine. Upon the chyme's entry into the small intestine, the pancreatic juice joins in to help break down the carbohydrates into single sugar, which are then transported into intestinal cells.
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Absorption of Carbohydrates Going Through Blood Stream
The small intestine cells have membranes containing many transport proteins to get the monosaccharides and other nutrients into the blood, which can be distributed to the rest of the body. The carbohydrates we eat are digested into simple sugars like glucose, fructose, and galactose.
The liver is the first organ to receive glucose, fructose, and galactose. The liver breaks fructose into smaller carbon-containing units and converts galactose to glucose. The final product from the digestion of carbohydrates is glucose, which is either used for energy or stored as triglyceride in fat or glycogen in muscle and liver. The liver either stores glucose as glycogen or exports glucose to the blood.
Glycogen in the Liver And Muscles
Humans and animals store glucose energy from starches in the form of the very large molecule glycogen. It has many branches that allow it to break down quickly when energy is needed by cells in the body. It is predominantly found in the liver and muscle tissue in animals.
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Maintaining Blood Glucose Level
The blood glucose level is tightly controlled by the synergy of various hormones, organs, and tissues in our bodies, as having either too much or too little glucose in the blood can have severe health consequences.
One of the glucose regulators in our bodies is located in the cells of the pancreas. After eating carbohydrates, glucose level rises in the blood. The increase in blood glucose level is sensed by pancreas insulin-secreting cells, which then release insulin into the blood. Insulin is a hormone made by the pancreas that helps glucose in blood enter cells in muscle, liver, and fat, where it is used or stored. In muscle tissue and the liver, insulin sends the biological message to store glucose as glycogen.
Insulin in the blood signifies to the body cells that glucose is available for fuel. Insulin signals the body’s cells to remove glucose from the blood. Blood glucose levels decrease as glucose is transported into the cells around the body. Insulin has an opposing hormone called glucagon. The pancreas also produces glucagon. Glucagon-secreting cells in the pancreas sense the drop in glucose and, in response, release glucagon into the blood. Glucagon stimulates increases in blood sugar levels, thus opposing the action of insulin. Glucagon signals the liver to break down glycogen and release the stored glucose into the blood so that glucose levels stay within the target range and all cells get the needed fuel to function normally.
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Digesting Carbohydrates
The less starchy complex carbohydrates are broken down into simple carbohydrates in the small intestine.
All non-glucose monosaccharides are converted into glucose in the liver and released into the bloodstream. It is used immediately or converted into glycogen, a polysaccharide of glucose stored in the liver and muscles for later use.
Fibre refers to any complex carbohydrates that can not be broken down by the digestive enzymes in the small intestine. This fibrous matter moves into the large intestine, where it helps produce beneficial short-chain fatty acids and nourishes the lining of the gut.
Generally, carbohydrates in their natural, fiber-rich form are more nutritious than those stripped of their fiber content. Fruits and vegetables are excellent sources of carbohydrates.
Fiber Digestion in the Large Intestine
Almost all carbohydrates, except dietary fiber and resistant starches, are efficiently digested and absorbed into the body. Some of the remaining indigestible carbohydrates are broken down by enzymes released by bacteria in the large intestine. The products of bacterial digestion of these slow-releasing carbohydrates are short-chain fatty acids and some gases. The yield of energy from the dietary fiber is about two calories per gram but is highly dependent upon the fiber type, with soluble fibers and resistant starches yielding more energy than insoluble fibers. Since dietary fiber is digested much less in the gastrointestinal tract than other carbohydrate types (simple sugars, many starches), the rise in blood glucose after eating them is less and slower. These physiological attributes of high-fiber foods like whole grains are linked to a reduction in weight gain and reduced risk of chronic diseases, such as Type 2 diabetes and cardiovascular diseases.
