What Is Glucose?

Glucose comes from the Greek word for "sweet." It's a type of sugar you get from foods you eat, and your body uses it for energy. As it travels through your bloodstream to your cells, it's called blood glucose or blood sugar.

Insulin is a hormone that moves glucose from your blood into the cells for energy and storage. People with diabetes have higher-than-normal levels in their blood. Either they don't have enough insulin to move it through or their cells don't respond to insulin as well as they should.

High blood glucose for a long period of time can damage your kidneys, eyes, and other organs.

How Your Body Makes Glucose

It mainly comes from foods rich in carbohydrates, like bread, potatoes, and fruit. As you eat, food travels down your esophagus to your stomach. There, acids and enzymes break it down into tiny pieces. During that process, glucose is released.

It goes into your intestines where it's absorbed. From there, it passes into your bloodstream. Once in the blood, insulin helps glucose get to your cells.

Energy and Storage

Your body is designed to keep the level of glucose in your blood constant. Beta cells in your pancreas monitor your blood sugar level every few seconds. When your blood glucose rises after you eat, the beta cells release insulin into your bloodstream. Insulin acts like a key, unlocking muscle, fat, and liver cells so glucose can get inside them.

Most of the cells in your body use glucose along with amino acids (the building blocks of protein) and fats for energy. But it's the main source of fuel for your brain. Nerve cells and chemical messengers there need it to help them process information. Without it, your brain wouldn't be able to work well.

After your body has used the energy it needs, the leftover glucose is stored in little bundles called glycogen in the liver and muscles. Your body can store enough to fuel you for about a day.

After you haven't eaten for a few hours, your blood glucose level drops. Your pancreas stops churning out insulin. Alpha cells in the pancreas begin to produce a different hormone called glucagon. It signals the liver to break down stored glycogen and turn it back into glucose.

That travels to your bloodstream to replenish your supply until you're able to eat again. Your liver can also make its own glucose using a combination of waste products, amino acids, and fats.

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Blood Glucose Levels and Diabetes

Your blood sugar level normally rises after you eat. Then it dips a few hours later as insulin moves glucose into your cells. Between meals, your blood sugar should be less than 100 milligrams per deciliter (mg/dl). This is called your fasting blood sugar level.

There are two types of diabetes:

  • In type 1 diabetes, your body doesn't have enough insulin. The immune system attacks and destroys cells of the pancreas, where insulin is made.
  • In type 2 diabetes, the cells don't respond to insulin like they should. So the pancreas needs to make more and more insulin to move glucose into the cells. Eventually, the pancreas is damaged and can't make enough insulin to meet the body's needs.

Without enough insulin, glucose can't move into the cells. The blood glucose level stays high. A level over 200 mg/dl 2 hours after a meal or over 125 mg/dl fasting is high blood glucose, called hyperglycemia.

Too much glucose in your bloodstream for a long period of time can damage the vessels that carry oxygen-rich blood to your organs. High blood sugar can increase your risk for:

People with diabetes need to test their blood sugar often. Exercise, diet, and medicine can help keep blood glucose in a healthy range and prevent these complications.

WebMD Medical Reference Reviewed by Michael Dansinger, MD on August 13, 2016

Sources

SOURCES:

American Diabetes Association: "The Liver's Role: How It Processes Fats and Carbs."

American Foundation for the Blind: "What is the Difference Between Hyperglycemia and Hypoglycemia?"

Group Health: "How Our Bodies Turn Food Into Energy."

Insel, P. Nutrition, 2004.

Joslin Diabetes Center: "Goals for Blood Glucose Control," "High Blood Glucose: What it Means and How to Treat it."

National Institute of Diabetes and Digestive and Kidney Diseases: "Insulin Resistance and Prediabetes," "Your Guide to Diabetes: Type 1 and Type 2."

NCBI: "Molecular Biology of the Cell, 4th Edition."

UCSF: "The Liver & Blood Sugar."

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