The second-messenger system is a set of intracellular molecules that are activated by cell surface receptors and affect cell function, producing a physiological response.

• 第二信使是被膜受体激活的胞内分子；通过浓度变化传递信号；影响细胞功能.；胞外的各种信号转换成胞内单一的信号；细胞只需读取这个第二信号；作出应答