Insulin pump maker Tandem Diabetes Care (NASDAQ: TNDM) has secured an FDA OK that puts it on track to challenge Medtronic (NYSE: MDT) for the lead in the emerging market for closed-loop insulin systems. Is Tandem Diabetes stock a buy? Produced by beta cells in the pancreas, insulin is necessary for removing glucose from the bloodstream so it can be stored in the liver and muscles for energy.Image source: Getty Images.Continue reading