Together, insulin and glucagon help keep conditions inside the body steady. When blood sugar is too high, the pancreas secretes more insulin. When blood sugar levels drop, the pancreas releases glucagon to bring them back up.
Blood sugar and health
The body converts carbohydrates from food into sugar (glucose), which serves as a vital source of energy. Blood sugar levels vary throughout the day but, in most instances, insulin and glucagon keep these levels normal.
Health factors including insulin resistance, diabetes, and problems with diet can cause a person's blood sugar levels to soar or plummet.
Blood sugar levels are measured in milligrams per decilitre (mg/dl). Ideal blood sugar ranges are as follows:
- Before breakfast - levels should be less than 100 mg/dl for a person without diabetes and 70-130 mg/dl for a person with diabetes.
- Two hours after meals - levels should be less than 140 mg/dl for a person without diabetes and less than 180 mg/dl for a person with diabetes.
The pancreas releases insulin and glucagon (shown here in purple and green) to control blood sugar levels.
Blood sugar levels are a measure of how effectively an individual's body uses glucose. When the body does not convert enough glucose for use, blood sugar levels remain high. Insulin helps the body's cells absorb glucose, lowering blood sugar and providing the cells with the glucose they need for energy.
When blood sugar levels are too low, the pancreas releases glucagon. Glucagon forces the liver to release stored glucose, which causes the blood sugar to rise.
Insulin and glucagon are both released by islet cells in the pancreas. These cells are clustered throughout the pancreas. Beta islet cells (B cells) release insulin, and alpha islet cells (A cells) release glucagon.
How insulin works
The body converts energy from carbohydrates into glucose. The body's cells need glucose for energy, but most cells cannot directly use glucose.
Insulin acts like a key to allow glucose to access the cells. It attaches to insulin receptors on cells throughout the body, telling those cells to open up and allow glucose to enter.
Low levels of insulin are constantly circulating throughout the body. When insulin rises, this signals to the liver that blood glucose is also high. The liver absorbs glucose, then changes it to a storage molecule called glycogen.
When blood sugar levels drop, glucagon signals the liver to convert the glycogen back to glucose. This makes blood sugar levels go up.
Insulin also supports healing after an injury by delivering amino acids to the muscles. Amino acids help build the protein found in muscle tissue, so when insulin levels are low, muscles may not heal properly.
How glucagon works
The liver must store glucose to power the cells during times of low blood sugar. Skipping meals and poor nutrition can lower blood sugar. By storing glucose, the liver makes sure blood glucose levels stay steady between meals or during sleep.
When blood glucose falls, cells in the pancreas secrete glucagon. Glucagon instructs the liver to convert glycogen to glucose. This makes glucose more available in the bloodstream. From there, insulin attaches to insulin receptors on cells to make sure they can absorb glucose.
Insulin and glucagon work in a cycle. Glucagon interacts with the liver to raise blood sugar, while insulin lowers blood sugar by helping the cells to use glucose.
How blood sugar levels affect the body
Insulin and glucagon don't work straightaway, particularly if the blood sugar is very high or very low.
High blood sugar
Symptoms of high blood sugar include:
- Urinating more often than usual. The kidneys respond to high blood sugar by trying to get rid of excess glucose.
- Feeling excessively thirsty, especially if also urinating often. As the kidneys try to regulate blood sugar, it can cause dehydration and feelings of intense thirst.
- Feeling excessively hungry. This is not caused by high blood sugar, but by the low insulin effect that often goes with high blood sugar.
Excessive hunger and thirst are common symptoms of high blood sugar levels.
Over time, very high blood sugar may cause:
- unexplained weight loss
- slow healing times
- itchy, dry skin
- increased likelihood of infections
- fatigue or difficulty concentrating
- blurred vision
- constipation, diarrhea, or both
- erectile dysfunction
Delays between meals, poor nutrition, some diabetes medications, and some medical conditions can cause low blood sugar.
Symptoms of low blood sugar include:
- rapid heartbeat
- tingling, particularly in the tongue, lips, arms, or legs
- hunger alongside nausea
- confusion and difficulty concentrating
- seizures or loss of consciousness if untreated
Blood sugar issues caused by diabetes
Though lifestyle factors cause blood sugar shifts, the most common cause of blood sugar issues is diabetes.
There are several types of diabetes, which are described here:
Type 1 diabetes
Type 1 diabetes may be referred to as juvenile diabetes because it usually develops during childhood.
Type 1 diabetes causes the body's immune cells to attack some of the insulin-secreting cells in the pancreas.
People with type 1 diabetes often experience very high blood sugar. Their low insulin levels, however, mean that they cannot use much of the glucose in their blood.
Type 1 diabetes is a type of autoimmune condition, which means that it causes the body to attack itself. It often develops in childhood, and is sometimes called juvenile diabetes.
Type 2 diabetes
Type 2 diabetes is the most common type of diabetes, and is linked to lifestyle issues such as being overweight.
People with type 2 diabetes have insulin resistance. This means that insulin doesn't work as well to allow the cells access to glucose.
Gestational diabetes is a form of diabetes that occurs during pregnancy.
When a woman is pregnant, the placenta that supports the developing baby can undermine the body's ability to use insulin. This causes insulin resistance that triggers symptoms similar to those of type 2 diabetes.
Gestational diabetes usually goes away after the baby is born. However, it is a risk factor for the later development of type 2 diabetes.