Your body needs glucose to obtain the energy to function. Glucose is obtained by the body through eating carbohydrates. In each gram of carbohydrates you consume there are four calories worth of energy. Once ingested into the body, special enzymes in the digestive system break down the carbohydrates you have eaten into simple sugars called glucose. This breaking down process allows the body to access the calories of energy contained in the carbohydrate.
After eating a meal, the body goes to work to break down the carbohydrates to produce glucose. This glucose is released into the bloodstream, raising your blood sugar levels. For the cells to access the glucose in the bloodstream, your pancreas must produce a hormone called insulin. As your blood glucose levels start to rise, the pancreas is triggered to release insulin into the bloodstream. Without insulin the cells will be unable to absorb the glucose needed to obtain energy.
Problems with insulin either occur because there is not enough insulin being produced by the body, or the cells have become resistant to insulin. These problems are symptoms of a disease called diabetes. If not enough insulin is being produced, this can result in a dramatically low blood glucose level, which leaves the cells unable to produce enough energy to survive. If the cells become resistant to insulin, this can result in too much glucose circulating in the bloodstream, which can cause serious damage to the blood vessels of the body.
Each cell in your body has special equipment on them called insulin receptors. When these receptors come into contact with insulin, they are able to bind to it. This binding acts as a key to unlocking the cell's ability to draw glucose out of the bloodstream and into the cell itself. This is done through the glucose transporter molecules in the cell's membrane.
Once the glucose has entered the cell, the cell works to burn the glucose to create energy. This is done through a process called aerobic metabolism. During aerobic metabolism, oxygen is pulled from the blood and into the cell with the glucose. The mitochondria uses the oxygen to burn the glucose into heat energy and adenosine triphosphate (ATP). ATP is then used to store or release the energy created, depending on the cell's needs.