The word glucose comes from the Greek word for “sweet”. It is a type of sugar obtained from food that the body uses for energy. When glucose reaches the cells through the bloodstream, it is called blood sugar.
Insulin is a hormone that transports glucose from the blood to the cells for energy production and storage. People with diabetes have higher than normal levels of glucose in their blood. There may be a lack of enough insulin in the body to get glucose into the cells, or the cells may be less responsive to insulin than normal.
Prolonged high blood sugar can damage the kidneys, eyes, and other organs.
How does the body make glucose?
Glucose comes mainly from foods rich in carbohydrates, such as bread, potatoes, and fruit. When you eat, the food travels down the esophagus to the stomach. In the stomach, stomach acid and enzymes break down the food into small pieces. The process produces glucose.
Glucose then enters the intestine, where it is absorbed, and from the intestine into the bloodstream. Once in the bloodstream, insulin assists in getting glucose into the cells.
Energy and storage
The body needs to keep glucose levels in the bloodstream constant. The beta cells in the pancreas monitor blood glucose levels every few seconds. When blood sugar rises after eating, the beta cells release insulin into the bloodstream. Insulin acts like a key that unlocks muscle, fat, and liver cells so that glucose can enter them.
Most cells in the body use glucose, amino acids (the building blocks of protein), and fat as sources of energy. But glucose is the main source of energy for the brain. The nerve cells and chemical messengers in the brain need energy to help them process information. If there is a lack of energy, the brain cannot function properly.
When the body has used up the energy it needs, the remaining glucose is stored in parts of the liver and muscles called glycogen. The body can store enough energy sources to provide the energy it needs throughout the day.
Without eating for several hours, blood glucose levels drop. The pancreas stops producing insulin. The alpha cells in the pancreas will begin to secrete another hormone called glucagon. Glucagon signals to the liver to break down stored glycogen and convert it into glucose.
This glucose is transported to the bloodstream to replenish energy until it can be fed again. The liver can also use a combination of waste products, amino acids, and fats to produce glucose.
Glucose levels and diabetes
Glucose levels usually rise after eating. A few hours later, when insulin transfers glucose to the cells, blood glucose levels drop. Between meals, blood glucose should be below 100 mg/dl, which is also called the fasting blood glucose level.
There are two types of diabetes:
- In type 1 diabetes, the body fails to produce enough insulin. The immune system attacks and destroys the pancreatic cells (the cells that make insulin).
- In type 2 diabetes, the cells are less responsive to insulin. As a result, the pancreas needs to produce more insulin to transport glucose into the cells. Eventually, the pancreas becomes damaged and subsequently cannot produce enough insulin to meet the body’s needs.
Lacking enough insulin, glucose cannot enter the cells. Persistently high blood glucose levels. A high blood glucose level, called hyperglycemia, is defined as more than 200 mg/dl 2 hours after a meal or more than 125 mg/dl on a fast.
Prolonged high blood glucose levels in the blood can damage the blood vessels that carry oxygen-rich blood. Hyperglycemia increases the risk of:
- Heart disease, heart attack, and stroke;
- Kidney disease;
- Nerve damage;
- The eye disease called retinopathy.
People with diabetes need to test their blood sugar frequently. Exercise, diet, and medications help keep blood sugar in a healthy range and prevent these complications.