Which messenger type is often involved in hydrophilic hormone signaling?

In the context of hydrophilic hormone signaling, first messengers play a crucial role as they are the actual hormones that travel through the bloodstream and bind to specific receptors on the target cells. These first messengers, which are typically water-soluble substances, cannot easily cross the cell membrane due to their hydrophilic nature. Instead, they rely on receptors on the cell surface to initiate a signaling cascade within the cell.

When a first messenger binds to its receptor, it activates intracellular processes that could involve second messengers. These second messengers, such as cyclic AMP or calcium ions, facilitate further signaling pathways that lead to a cellular response. However, the initial signaling event is mediated by the first messenger. Thus, the role of first messengers is foundational in communicating hormonal signals within the body, particularly for hydrophilic hormones that operate through membrane-bound receptors.