can insulin and glucagon be in the circulation at any one time?

Absolutely, yes, sir, but they are counter-regulatory hormones, which means when one of them is being produced, it inhibits the production of the other. i.e. when blood sugar (glucose) levels fall, due to there being too much insulin present, the alpha cells (islets of Langerhans) produce the hormone glucagon, which stimulates the liver to 'give up' some of its reserves of glycogen ... the way it stores glucose. The production of glucagon temporarily 'shuts down' production of insulin, and vice versa.

It's normally a carefully controlled sub-system of homeostasis ... the keeping of the body 'in balance'.

Yes.

Mick,

Thx for this. Could not get a straight answer anywhere. You just did it in 5 lines. Grateful.

Steve