MICROANATOMY

Detailed explanation-1: -All hormones act only on their target tissues. The ability of a tissue to react to a hormone is due to the presence of a receptor in or at the cell. There are two classes of hormone receptors : those bound to the membrane and those present in the cytosol. Peptide hormones generally act through membrane receptors.

Detailed explanation-2: -Hormone binding to receptor activates a G-protein, which in turn activates adenylyl cyclase, converting ATP to cAMP. cAMP is a second messenger that mediates a cell-specific response. An enzyme called phosphodiesterase breaks down cAMP, terminating the signal.

Detailed explanation-3: -Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).