Insulin secretion and action, and the role of glucagon

At a glance

• Insulin is the only hormone that lowers glucose. Glucagon, adrenaline, cortisol and growth hormone raise it, in that order of speed.
• Beta cells sense glucose through glucokinase and couple it to secretion by closing the ATP-sensitive potassium (KATP) channel. Sulfonylureas act at this channel.
• Insulin is secreted into the portal vein, and the liver removes about 50% on first pass. Portal insulin suppresses hepatic glucose output far more than peripheral injection can, which is why injected insulin needs higher systemic levels.