Carbohydrate: Process of digestion

Carbohydrates in the diet provide the major exogenous source for glucose, which is the primary energy source for cells.

Carbohydrates are hydrophilic and require a series of reactions to digest them to monosaccharides which are absorbed in the small intestine. Carbohydrates consist of three main groups, simple carbohydrates (monosaccharides), disaccharides and complex carbohydrates (starch, glycogen, and fiber).The common monosaccharides include glucose, fructose, galactose, xylose and ribose.

Starch, the major food polysaccharide, consists of 85% amylopectin and 15% amylose. Amylose is composed of straight chains of glucose molecules linked through1:4-α bond where as amylopectin, in addition to chains of 1:4- α linked glucose molecules, also has 1:6- α links between glucose molecules in adjacent chains forming bridges.

When the person eat carbohydrates, such as a bowl of pasta or some vegetables, the digestive system breaks the carbohydrates down into simple sugars such as glucose, which travel into and through the bloodstream to nourish and energize cell.

The digestion process of polysaccharides such as starch will begin in the mouth where it is hydrolysed by salivary amylase. Chewing, also known as mastication, crumbles the carbohydrate foods into smaller and smaller pieces. The salivary glands in the oral cavity secrete saliva that coats the food particles. Salivary amylase breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides, and starches. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose.

The goal of carbohydrate digestion is to break down all disaccharides and complex carbohydrates into monosaccharides for absorption, although not all are completely absorbed in the small intestine (e.g.,fiber).

Fructose is absorbed by facilitated diffusion while glucose and galactose are actively transported. Glucose, at low concentrations is transported through the mucosal lining into the epithelial cells of the intestine by active transport, via a sodium dependant transporter. The first organ to receive glucose, fructose, and galactose is the liver. The liver takes them up and converts galactose to glucose, breaks fructose into even smaller carbon-containing units, and either stores glucose as glycogen or exports it back to the blood.
Carbohydrate: Process of digestion 

Glucose functions in human body

Glucose is a monosaccharide, which is derived from dietary carbohydrates. Glucose is the only simple sugar that is transported in the bloodstream and it is commonly referred to as ‘blood sugar’.

Human body derived the glucose they need primarily from starch, a carbohydrate produce by plants. Glucose is found naturally in fruits, honey, sugarcane, sugar beets sweet potatoes, parsnip, onions and many other vegetables.

In the digestive system, starch is broken down into glucose molecules. Glucose then enters the blood stream.

The body cells use as much glucose as they can for their energy needs of the moment. Excess glucose is linked together and stored as glycogen.

Glycogen is the form in which the body store glucose in the liver and skeletal muscle cells. Glycogen is composed of long, highly branched chains of glucose molecules. When the blood glucose levels fall the human body are able to convert liver glycogen into glucose, which is called glycogenolysis.

To handle the glucose that’s still coming in, body tissues shift to burning more glucose for energy instead of fat.

As a result, more fat is left to circulate in the bloodstream until it is picked by the fatty tissues and stored there.

In healthy individuals, a decline in blood glucose is normally prevented by homeostatic mechanisms. Serious problems can result in people whole glucose homeostasis is not operating properly.

A low level of glucose in the blood is called hypoglycemia. And is as harmful to the brain as is lack of oxygen.

A high level of glucose in the blood is called hyperglycemia and can lead to glucose in the urine – glycosuria.
Glucose functions in human body

Carbohydrates

Carbohydrates
Unlike proteins, the carbohydrates in the body contribute nothing to the structure of tissue and although they contribute to the regulation of metabolism, they do not control individual molecular events as the enzymes (proteins) do. Their major function is the provision of energy to a variety of tissues, especially to the brain and nervous system which cannot utilize other nutrients for energy.

The carbohydrates in a typical breakfast – toast and tea with milk and sugar – are roughly representative of the distribution of carbohydrate in the average diet: starch from bread, potatoes, rice, pasta: sucrose from sugar: and lactose from milk. Starch is large molecule made up of many glucose units joined together, all glucose units being of similar structure. It is rapidly digested to its basic glucose units which are readily absorbed.

Lactose and sucrose are by contrast very much small molecules, each of which is digested to become effectively (in the liver) two units. The enzymes responsible for their digestion are, respectively, lactase and sucrase. There is rarely a problem is the digestion of sucrose but a great number of number people encounter problems with lactose digestion, most of which are associated with and inadequate supply of lactase.

Undigested lactose passes from small intestine, where digestion and absorption of its glucose units should occur, into the large intestine, where bacteria (a normal non pathogenic population of microbes) ferment the lactose and cause digestive upsets and diarrhea. The bulk of the population of Africa, Southern Europe, and the near East develop lactose intolerance during later childhood and adult life.

Under normal conditions, however the great majority of carbohydrates in our typical meal are digested and absorbed as glucose, if you measured blood glucose levels before such a meal and at half hourly intervals thereafter, you would see a rise in blood glucose, peaking at about the half hour mark and returning to fasting levels almost as quickly. If you were to abstain from carbohydrates for a considerable period say a week, your blood glucose levels would still be normal in spite of a minimal or zero intake, the body’s capacity to maintain blood glucose within specific limits is achieved by a variety of hormones, the two most important of which are insulin and glucagon. Both are secreted by the pancreas into bloodstream, as required.
Carbohydrates