The extracellular matrix is the protein and carbohydrate scaffolding between cells that give cells and ultimately, tissues, their structure. Changes to this structure are critical during wound healing, which signals cells to migrate, proliferate and develop into specific tissues like new blood vessels.
Cytokines are chemicals released by white blood cells to signal that there has been cellular damage or infection. Cytokines recruit other blood cells to the area and the result is inflammation. Specific cytokines such as Interleukin-2 are used to recruit blood cells to fight some cancers.
Charged ions passing through the membranes of neurons can alter the voltage across a membrane and generate a signal that fires the nerve. These charges can travel from a burned finger to the brain in a fraction of a second, then back to the muscle to pull the hand away from the fire.
Hormones are system-wide communicators. Hormones such as thyroid, insulin, testosterone and estrogen are produced by glands and circulate throughout the body in the bloodstream. Insulin is produced by the pancreas and signals cells throughout the entire body when to absorb sugars.