Blood sugar/blood glucose levels are controlled by negative feedback involving the hormones human insulin and glucagon
Insulin is produced in the increased , if there is too little glucose in the blood the pancreas is triggered and released more insulin to change glucagon into glucose, this regulates the amount of glucose in the blood. However if there is too much glucose in the blood (after a sugary meal) the pancreas is triggered to use insulin to lower the blood glucose levels, this is called negative feedback. This works by storing glucose as glucagon in the blood, insulin can be objected into the blood stream if a person needs it straight away(eg type 1 diabetes)