All the cells present in the body receive and respond to signals. There are three signaling pathway endocrine signaling, paracrine signaling, and autocrine signaling through which cells receive the signals.
In endocrine signaling signal comes through blood, in paracrine signaling signals are released in extracellular fluid which reaches the cell present in close to it. In autocrine signaling, the same cell produces and receives the signals.
All cells have receptors that bind to the signal molecules and respond to the signals. These receptors can be extracellular or intracellular receptors. Extracellular receptors generally bind to hydrophilic molecules and intracellular receptor binds to lipophilic signal molecules.
This binding brings conformational change in the receptors which gives the signal to the cell to perform some function according to the signals provided. Thus this way all the cells respond to every signal.
Molecules that cannot cross the membrane bind to receptors in the membrane. When the signal binds to a receptor changes it's shape. Other Molecules inside the cell respond to the chainging shape of the receptor.
