Topic overview

Start with the big picture

Hormones are grouped as peptides, steroids, or amines, with their chemical properties influencing how they are made, stored, and transported. Peptides are water-soluble and typically act at cell membrane receptors; steroids are lipid-soluble and commonly bind intracellular receptors. Amine hormones show both patterns: catecholamines signal through membrane receptors, while thyroid hormones act through nuclear receptors. Hormonal signaling may use second messengers such as cAMP or IP₃/DAG, or directly regulate gene transcription. The broader lesson connects these mechanisms with hormone transport and half-life, receptor availability, and feedback. Together, these principles explain why hormones with different structures can produce distinct signaling pathways and how target-cell responsiveness can change.