What distinguishes steroid hormones from peptide hormones?

• A. Steroid hormones are water-soluble; peptide hormones are lipid-soluble.
• B. Steroid hormones bind to receptors on cell surfaces; peptide hormones can pass through membranes.
• C. Steroid hormones can pass through cell membranes; peptide hormones are water-soluble.
• D. Both types of hormones are hydrophilic.

Answer: (C)

The correct answer emphasizes a fundamental distinction between steroid hormones and peptide hormones in terms of their solubility and ability to interact with cell membranes. Steroid hormones are lipid-soluble, which allows them to pass through cell membranes easily. This property enables them to bind to intracellular receptors located inside the target cells, leading to direct modulation of gene expression.

Peptide hormones, on the other hand, are typically water-soluble and cannot easily cross cell membranes due to their hydrophilic nature. Instead, they bind to specific receptors on the surface of the target cells, initiating a cascade of intracellular signaling pathways without entering the cell. This difference in solubility and route of action is critical for their respective physiological roles and mechanisms of action in the body.

This understanding of hormone behavior is essential for grasping how hormonal signaling operates in various biological processes and their implications in health and disease.