Where do circulating hormones act in the body?

Circulating hormones act on cells with special receptors, which is the correct understanding of how hormones function in the body. Hormones are chemical messengers released into the bloodstream by endocrine glands, and they travel to target cells that possess specific receptors for those hormones. This interaction is crucial because the hormone-receptor binding triggers a response within the target cell, leading to various physiological effects.

When a hormone binds to its specific receptor on a target cell, it initiates a cascade of biological responses tailored to that particular hormone's function. For instance, insulin acts on cells with insulin receptors, facilitating glucose uptake. This targeted approach ensures that hormones can effectively regulate processes such as metabolism, growth, and mood.

This mechanism distinguishes the action of hormones from other forms of signaling in the body, such as paracrine signaling, where substances act on neighboring cells, or autocrine signaling, where cells respond to signals that they release themselves. Also, the notion that hormones only act on the glands that release them or solely at the site of release doesn't adequately describe the systemic nature of hormonal action throughout the body. Instead, hormones circulate broadly but only exert their effects on cells designed to respond to them.