Glucose is sugar. The body is able to break down many kinds of food into glucose to provide us with energy. Blood sugar levels increase after we eat or drink anything other than water, and therefore we do not need all the sugar and sweets that we eat.
Every cell in our body needs energy just to stay alive, and glucose provides the basic fuel which the body burns. Glucose and fructose are the two most important examples of a group of sugar- compounds found in various foods such as fruit, (fructose) and milk (lactose). They are all changed to glucose when they are absorbed into the body. The ordinary white sugar that we buy is actually a substance called sucrose, which is glucose combined with sugar. It is energy-producing, but is now blamed for all kinds of physical ills.
All the various sugars are made of the same three chemical elements – carbon, hydrogen and oxygen. So this change to glucose is not as complicated as it seems. The only difference between them is the hydrogen and oxygen atoms are ‘hung’ onto the carbon backbone in slightly different arrangements. This simple chemical structure gives the name ‘carbohydrates’ to all the foods that are based on sugar molecules.
Breaking down Starch
One of the tasks of the digestive system is to break down starch-based carbohydrates such as potatoes and bread, into individual sugar molecules. This process starts in the mouth, where there is a starch-splitting enzyme called amylase, which is found in saliva. More amylase is mixed with food that is passed down through the stomach into the intestine.
Amylase breaks the starch down into pairs of sugar molecules, which are then split by another series of enzymes in the small intestines so that only individual sugar molecules are absorbed. Finally, the sugars are carried to the liver in the bloodstream. The liver changes all fructose and other similar compounds into glucose.
How does glucose work?
The body has many mechanisms which make sure there is an ample level of glucose in the bloodstream to supply its needs. These depend on switching on or off the release of glucose that is stored in the liver. Glucose is stored as a compound called glycogen, which is a loose nit mesh of glucose molecules. Glycogen is also stored into the muscle.
Once glucose is released into the bloodstream, it is taken up by the cells. To do this insulin is essential. Insulin like amylase, also comes from the pancreas. But, unlike amylase it is secreted into the blood not into the intestine.
When glucose is inside the cells, it is burnt with oxygen to produce energy. Carbon dioxide gas and water are the waste products of this process. The carbon dioxide is carried in the blood to the lungs, where it is extracted back into the air, while the water simply joins the pool making up 70% of the body weight.
Just as liver stores glucose, in the form of glycogen, so the energy made from burning glucose has itself to be stored in each cell, to be used little by little to provide power for the chemical reaction which the cells depend. The cells do this by creating high-energy phosphate compounds which are easily broken down to release the energy. These phosphate compounds (adenosine triphosphates or ATP) are like a battery that can be used and recharged at will, to small amounts of energy as they are needed. The recharging comes from burning glucose.
Other sources of energy
The storing of glucose-producing glycogen in the body are not very large and if they run down other sources are necessary. The body has two solutions to this problem. First it may start to convert protein – the main structural compound of the body – into glucose. Secondly, it may start to burn fat in the tissue instead of glucose. The fat provides just a good a source of energy as glucose, but in doing so produces extra waste products called ketones.
Control of Glucose levels
Since glucose is such an important fuel, its levels in the bloodstream need to be keep in fairly defined limits, if we are to remain in good health. Too high a level of blood glucose (hyperglycemia) can be sign of diabetes, the condition where the blood sugar level permanently raised.
If the glucose levels fall too low (hypoglycemia), the brain can no longer function properly and loss of consciousness results. The blood glucose level in our bodies is kept constant by balancing the effects of insulin (which lowers blood glucose by pushing it into cells) with a whole range of other hormones, all of which tend to push the blood glucose up by releasing glucose from the liver. The most important are adrenaline and cortisone, both of which come from the adrenal gland. Another, called growth hormone, comes from the pituitary gland in the brain. This also tends to increase the amount of glucose in the blood.
Although increased blood sugar is a symptom that something is seriously wrong, the excess of glucose is not harmful in itself. In a healthy individual, a brief increase, after eating a quantity of sweets for example, will only cause a passing disturbance in the bodies regulatory system. But constant overloading with sugars may be harmful. It is only sensible to try to eat less.