Sugar, the main source of energy
Sugar is a simple carbohydrate and when absorbed into the body acts as a source of quick-energy. Thus, when sugar is consumed, it is at once absorbed into the blood stream and an increase in blood sugar level is observed. It is because of this that sugar is considered as a calorie dense food.
The main purpose of the digestion and absorption of sugars is to convert all the complex carbohydrates to simpler sugars. The simpler sugars are especially the glucose. When a person consumes food containing starch, the enzymes act upon starch to hydrolyze the long chains to shorter chains, which are finally converted to monosaccharide. The digestion of starch starts right from the mouth itself. The food is thoroughly mixed with the salivary and is called the bolus. The flow of saliva is also increased here. The swallowed bolus mixes with the stomach acid and protein-digesting enzymes, and these digest the salivary amylase. The starch gets broken down to simpler carbohydrates to some extent by the stomach acid.
The major carbohydrate digesting enzyme, pancreatic amylase, lies in the small intestine. The enzyme enters the intestine through the pancreatic duct and continues breaking down the polysaccharides to shorter glucose chains and disaccharides. The last step takes place in the intestinal cells. Here, maltose is broken down to two glucose molecules by the action of maltase, sucrose is broken down to one molecule of glucose and one molecule of fructose by the action of sucrase, and lactose breaks up into one molecule of glucose and one molecule of galactose by the action of lactase. Intestinal cells absorb these monosaccharides. Also, fiber is not digested in the small intestine and it delays absorption of other nutrients.
The digestion of a majority of starches and sugars is completed within four hours of digestion and only a small portion of the undigested fibers remains in the digestive tract. In the large intestine most of the fiber passes intact through the digestive tract to the large intestine. Here, the bacterial enzymes digests the fiber and are converted to fatty acids and gas. The fiber holds water, regulates bowel activity and binds with other substances such as bile, cholesterol, some minerals and thus carries them out of the body.
All the complex carbohydrates are broken down into simpler forms known as glucose so that it could be absorbed in to the blood stream. The monosaccharides travel across the intestinal cells and get absorbed in to the blood stream. The glucose thus absorbed is transported to target organs through blood in order to provide the necessary energy.
The absorbed blood circulates through the liver, whose cells takes up fructose and glucose and converts them to glucose. The glucose is the only source of energy to the body. The body does not have the capacity to utilize fructose.
Role of hormones in maintaining blood sugar level:
When a person eats, the blood glucose level rises. This high blood glucose level stimulates the pancreas to release insulin. The insulin stimulates the uptake of glucose into the cells and the excess glucose is stored as glycogen in the muscle and liver. Insulin also stimulates the conversion of excess glucose into fat for storage. As a result the blood glucose level diminishes. This low blood glucose stimulates the pancreas to release glucagons into the blood stream. Glucagon stimulates liver cells to break down glycogen and release glucose into the blood. Thus blood glucose level rises. The stress hormone epinephrine and other hormones also bring glucose out of storage.
Functions of glucose:
The main and important function of glucose in the blood is to provide energy that is required in order to carry out various physical activities is the body. Carbohydrates are the primarily used as the source of energy. In order to provide the body with the essential energy, adequate intake of carbohydrate rich sources are required. If adequate amounts of glucose are not available for the body, then proteins and fats are made use of as a source of energy. Proteins have the capacity of converting themselves to glucose that can be used as an energy source. The conversion of protein to glucose is called gluconeogenesis. This process is prevented only if the dietary intake of carbohydrate is adequate.
Insufficient intake of glucose also leads to a condition called ketosis. This occurs due to the deficient supply of glucose in the diet. This disturbs the acid base balance of the body. In order to prevent this condition, the daily carbohydrate intake of the individual should be 50 to 100 grams of carbohydrates. Also, if the intake of carbohydrates exceeds in the diet, then the excess glucose is converted into fat.
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