Away From the Bench

The world outside of the lab

Is That a Pancreas in Your Pocket?

When most people hear the term ‘vital organ,’ the pancreas doesn’t usually pop into their head.  However, the pancreas is vital for survival, keeping your blood sugar in check. That’s why artificial pancreas trials are so exciting.  A majority of Type 1 diabetics are diagnosed as children or teenagers, and must live the rest of their life with insulin injections or insulin pumps, which they control themselves. Having a machine to automatically adjust insulin and glucagon injections based on continuous blood glucose monitoring would make diabetic life much easier.  This is especially important in young children and during times when awareness of low blood sugar is impaired by low blood sugar itself (or during sleep), as the brain needs 6 grams of glucose per hour to function properly.  When blood sugar levels drop too low (hypoglycemia), a person can go into a coma or die because their brain and organs are not getting enough glucose as fuel to survive.

When you eat a meal, carbohydrates and other sugars get broken down or converted into glucose, which circulates through the bloodstream.  The pancreas contains clusters of endocrine cells (cells that secrete hormones into the bloodstream) called Islets of Langerhans.  The majority of cells in the islet are beta cells which secrete insulin and alpha cells which secrete glucagon.  The beta cells sense the glucose concentration in the blood and secrete insulin in response, which travels through the bloodstream to other organs.  The insulin signals to those tissues (such as muscle, liver, and fat) to take up the glucose from the blood into the cell to be used for energy or stored for energy later.  High blood sugar (hyperglycemia) results from lack of beta cells (in the case of Type 1 diabetics) and the tissues ‘starve’ because they are not getting the signal to take up and process glucose from the bloodstream.  The body then tries to remove the glucose from the blood through excess urine production.  This is why poor glycemic control over time can damage the kidney and transplants may be necessary, although hyperglycemia causes many other complications such as microvascular diseases and nerve damage.

Normally, when a person becomes hypoglycemic, glucagon is secreted from pancreatic islet alpha cells, traveling through the bloodstream to the liver.  Glucagon signals to the liver to break down glucose stores (stored in long, branching chains called glycogen) and release glucose into the bloodstream.  If both insulin and glucagon are provided in a regulated manner, blood glucose levels can be adjusted accordingly.

Copyright discoverysedge.mayo.edu

The current insulin pumps provide a basal infusion of insulin to help keep blood glucose levels steady, but they are under the control of the user and must be manually adjusted throughout the day, especially during eating (more insulin) or exercise (less insulin).  Most diabetics prick their finger several times a day to test their blood glucose levels, as continuous blood glucose sensors are not widely used and still need calibrated at least twice a day with finger pricks.  People using insulin must be aware of rapid declines in their blood glucose levels; if their blood sugar drops too low, they must eat or drink high sugar foods or injest glucagon tablets to restore normal glycemia.  It is imperative that artificial pancreas blood glucose sensors are accurate and able to sense downward trends exceedingly well.  If a person starts exercising, muscle tissue is more sensitive to insulin and can even take up glucose independently of insulin because the need for energy (glucose) is greater.  If the sensor cannot perceive the drop in glycemia quickly and accurately; confusion, coma, and death may follow.  Combining better automatic blood glucose sensing with insulin and glucagon infusion in a bionic pancreas is a major step towards creating a better life for diabetics.  Getting the technology reliable enough is the challenge.

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