The system is an example of a signal transduction pathway . Signal transduction pathways amplify responses to hormones through a cascade of reactions. Hence, a single hormone molecule combining with its receptor can stimulate production of many molecules of a particular cellular product. Figure 38.14 illustrates the cascade process. A single molecule of epinephrine can lead to production of billions of molecules of glucose by the liver.
Hormones diffuse away or are degraded by enzymes.
This system is illustrated in Figure 38.15 . Calcium Ions Calcium ions are important in many cellular functions such as opening ion channels and stimulating secretion. Some cell surface receptors can trigger gene transcription. This is accomplished through activation of cAMP response element-binding protein or CREB . Figure 38.16 illustrates this type of activation and gene transcription.