Match each description with the
Molecules that are released and
act within an organ on nearby
cells, allowing cells of an organ
to regulate one another.
Regulatory chemicals that are
secreted into the extracellular
fluid, carried by blood, and act at
a distance from its source.
Signaling molecules that affect
the cell's own behavior; for
example, this is common in the
immune system.
Chemicals that are released into
the environment for
communication between
individuals of a single species.
Molecules that are released into