What hormone type requires cell surface receptors to exert its effects?

Water-soluble hormones require cell surface receptors to exert their effects because they cannot easily cross the lipid bilayer of the cell membrane due to their hydrophilic nature. These hormones, such as insulin and epinephrine, bind to specific receptors on the outer surface of target cells. This binding triggers a series of intracellular signaling pathways that lead to a physiological response, such as altering gene expression, modifying enzyme activity, or changing the permeability of the cell membrane.

In contrast, lipid-soluble hormones, like steroid hormones and thyroid hormones, can pass through the lipid bilayer and typically bind to intracellular receptors. These interactions usually result in direct modulation of gene expression within the nucleus, leading to a longer-lasting effect on the cell.

Therefore, the distinction between the hormone types based on their solubility is crucial in determining how they interact with cells and elicit their respective biological responses.