Everyone knows that glucose, or sugar, is needed to give the human body energy. That would not be possible without the intervention of the hormone insulin -- a protein produced by the pancreas that responds to sugar levels in the blood. Pancreatic cells take up blood sugar and secrete insulin into the bloodstream. The insulin allows other body organs -- including the brain, liver, heart and muscles -- to take up sugar to fuel their own energy requirements.
Insulin is made and released by a type of cell in the pancreas known as a beta cell. This process is complex and occurs in response to changes in glucose concentration in the blood. Glucose concentration is affected by a person’s nutritional status, for example, if the person just ate a full meal or has been fasting for several hours. It is also influenced by hormones released by the intestines that are involved in the digestion of what has been eaten. Further, the brain releases factors into the blood based on its energy status and requirements.
A cascade of events begins when a person has eaten something, for example, a piece of bread. Bread is rich in carbohydrates, which when broken down by digestion become the sugar glucose. Glucose is absorbed by the intestines into the bloodstream, raising the blood glucose level, and transported to the pancreatic beta cells. Here it is broken down further into energy known as ATP, and this causes insulin to be released into the blood. Insulin then interacts with the body’s cells and organs, prompting them to absorb glucose from the blood to make their own energy. For example, the heart muscle needs glucose to make energy to sustain its pumping action.
Decreasing Blood Sugar
This movement of glucose into the body's cells lowers the levels of sugar in the blood. As blood sugar levels drop, they no longer stimulate the pancreas and insulin secretion stops. This type of regulatory feedback is important, because if too much insulin is available, blood sugar drops dangerously low and can potentially lead to a person’s death. One possible reason for excess insulin production would be insulinomas, or insulin-producing tumors of the pancreas. Symptoms of low blood sugar include sweating, rapid heartbeat, shakiness, confusion and, if not treated, seizures and coma.
A Careful Balance
Healthy adults produce about 33 units of insulin per day. Insulin is the only hormone available for reducing glucose concentration in the blood. This is in contrast to six hormones used to increase blood sugar levels, including cortisol, epinephrine, glucagon, thyroxine, adrenocorticotropin and somatotropin. The human body is in a constant state of balance between anabolism, the fed state involving insulin secretion and glucose uptake and storage, and catabolism, the fasting state. When fasting, the antagonists of insulin will cause storage sugar breakdown and release from the liver, thereby elevating blood sugar levels in times of energy need.
- Update on General Medicine: Eric P. Purdy, MD, et.al.
- The Journal of Clinical Investigation: Dynamics of Insulin Secretion and the Clinical Implications for Obesity and Diabetes
- Beta Cell Biology: Insulin From Secretion to Action
- International Journal of Endocrinology: A Twenty-First Century Cancer Epidemic Caused by Obesity -- The Involvement of Insulin, Diabetes and Insulin-like Growth Factors
- World Journal of Gastroenterology: Diagnosis and Management of Insulinoma