In my next several blogs, I want to discuss problems with glucose metabolism. Before I do, though, I thought I should explain exactly what glucose is and what we use it for.
Glucose is a molecule that contains six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen. Almost all glucose in the human body exists in a cyclic form that looks like this:
The chemical bonds between the atoms that form the glucose molecule contain energy that your body needs to function. If that energy was released all at once, though, you would literally blow up! So, your body, through a complicated series of chemical reactions, takes the energy in glucose molecules and stores it in other molecules called adenosine triphosphate (ATP). When your body needs energy for an activity, say moving a muscle, chemical bonds in ATP molecules break apart, releasing the energy in a form your body can use.
glucose + oxygen → carbon dioxide + water + Energy (stored in ATP molecules)
While your body can also use energy stored in fat molecules and protein molecules, it prefers to use energy from glucose molecules. Some cells require glucose for energy, except under unusual circumstances. Cells in your brain, for example, must use glucose for energy unless you have been without food for a long time. Amazingly, glucose can also be changed into other molecules when needed. Fat molecules can be made from glucose, as well as many amino acids (the molecules used to build proteins), and nucleic acids (DNA and RNA).
Your body needs to keep the amount of glucose in your blood relatively stable, no matter what you have eaten and no matter how active you have been. If you have eaten a food containing carbohydrates (the best source for glucose), glucose will enter your bloodstream. Some of that glucose will be used to meet your immediate energy needs, and some will be stored for future use. To store glucose for future use, your pancreas secretes a hormone called insulin. If your body responds to insulin normally, the insulin will cause glucose to move from your blood into your muscle and liver cells, where it will be stored in molecules called glycogen. If you can’t store any more glucose as glycogen, and you still have excess amounts of glucose, your body will turn it into adipose tissue (fat!).
If your dietary intake of glucose isn’t sufficient for your energy needs, your pancreas secretes another hormone called glucagon. Glucagon causes the glycogen molecules in your muscle and liver cells to break apart, releasing glucose into your blood so that you can use it to create enough ATP molecules for your energy needs. If you haven’t eaten for a long time, and used up all your glycogen, your body can even convert other molecules, such as fats and proteins, into glucose.
So, you can see that keeping your blood glucose levels is very important to your body. If your blood glucose levels get too high (hyperglycemia), damage can occur to blood vessels throughout your body, including the kidneys, eyes, and heart. High blood sugar levels can also damage nerves, promote the growth of cancerous cells, and make infection more likely. If blood glucose levels get too low (hypoglycemia), the brain won’t be able to function as it should, leading to dizziness, fainting, and possibly permanent brain damage or death.
If your body can’t maintain glucose in the normal range, doctors will say you have an impairment in glucose metabolism. The most well known disorder of glucose metabolism is diabetes. In diabetes, the pancreas either stops producing insulin (Type I diabetes) or cells don’t respond normally to the insulin that is made (Type II diabetes). In both cases, blood glucose levels will rise dangerously high without appropriate treatment. The American Diabetes Association (2013) estimates that 25.8 million Americans currently have diabetes, and an additional 79 million Americans currently have prediabetes. People with prediabetes also have impaired glucose metabolism, but their blood sugar levels don’t rise as high as those with diabetes.
In my next post, I’ll talk more about prediabetes and its dangers.
American Diabetes Association. (2013) Fast Facts: Data and Statistics about Diabetes. Retrieved June 9, 2014, from http://professional.diabetes.org/admin/UserFiles/0%20-%20Sean/FastFacts%20March%202013.pdf