Which type of hormone can pass through the cell membrane most easily?

Lipid or steroid hormones can pass through the cell membrane most easily due to their chemical structure. These hormones are hydrophobic, which allows them to dissolve in the phospholipid bilayer of the cell membrane without the need for special transport mechanisms. Once inside the cell, they can bind to intracellular receptors and influence gene expression directly.

In contrast, peptide hormones, amino acid hormones, and protein hormones are generally hydrophilic and cannot readily penetrate the lipid bilayer of the cell membrane. They typically require specific receptors on the cell surface to exert their effects, triggering a cascade of cellular responses without entering the cell itself. This distinction is crucial in understanding how different types of hormones interact with target cells and the mechanisms of hormonal signaling.