There are 2 main hormones regulating blood sugar levels. They are called insulin and glucagon.
When we eat something suggary (like a banana), the consequent rise in blood glucose level causes the pancreas to produce INSULIN (which promotes glucose difusion to the muscles and livre, lowering blood glucose). Later when the blood glucose is consumed for energy production, the blood sugar level decreases signaling the pancreas to produce GLUCAGON (which promotes glucose storage mobilization, rising blood glucose)