Canadian Health Information Management Association Practice Exam

Since insulin released from the pancreas is carried in the bloodstream to distant target cells, how is it classified?

1. Autocrine.

2. Circulating hormone.

3. Local hormone.

4. Neurotransmitter.

The correct answer is: Circulating hormone.

Insulin is classified as a circulating hormone because it is produced in the pancreas and secreted directly into the bloodstream. Once in the blood, it travels throughout the body to reach various target cells where it exerts its effects on glucose metabolism. This classification is essential because it differentiates insulin from other types of signaling molecules. Circulating hormones, like insulin, have a systemic effect, influencing distant tissue functions. In contrast, local hormones act in the immediate vicinity of their release, typically influencing neighboring cells rather than distant targets. Autocrine signaling involves cells responding to the substances they secrete themselves, and neurotransmitters are specific chemical messengers released from neurons to communicate with other cells across synapses. Hence, these other classifications do not apply to insulin as it has a broader systemic role rather than local or self-targeted effects.