When cells release ligands they are sent though the blood stream to every area of the body why do you think that only certain types of cells will reapond to a particular ligand?

Answer 1

The molecule has a recepter binded is and thius binding changes the shape which is critial for the affects on how a receptor interacts with other molecules.

Answer 2

Only certain cells respond to a specific ligand because they express the appropriate receptor on their cell surface that can bind to the ligand. The binding of the ligand to the receptor triggers a specific signaling pathway within the cell that leads to a response. Cells without the corresponding receptor will not respond to that particular ligand.