Hormones can be classified into distinct categories, primarily steroid hormones, which can directly pass through cell membranes, and peptide hormones, which require surface receptors to initiate cellular responses. Peptide hormones consist of short chains of amino acids, while polypeptide hormones are longer chains, each interacting with specific receptors to regulate various physiological functions. Understanding these differences is crucial for grasping how the endocrine system operates.
