What are the types of signaling molecules?

Signaling molecules are molecules that transmit information between cells, which is essential for maintaining homeostasis, coordinating responses in the body, and processing external stimuli in multicellular organisms. There are 4 types of signaling molecules: 

• Hormones – Hormones are the signaling molecules used in endocrine signaling, which is a form of long distance signaling. Hormones originate from endocrine cells and travel between endocrine cells and their target cells at distant body sites via the bloodstream. There are several different types of hormones that regulate various processes in the body and help to maintain homeostasis. 
• Local transmitters – Unlike hormones, local transmitters act locally to influence the behavior of nearby cells. They are used in paracrine signaling, which is a form of short range signaling. In this form of signaling, local transmitters that are released by one cell act on neighboring target cells by moving through the extracellular matrix between the two cells. 
• Neurotransmitters – Neurotransmitters are a diverse group of small hydrophilic molecules that transmit signals between neurons or from neurons to other target cells such as muscle cells. An action potential that reaches the terminus of a neuron, triggers the release of neurotransmitters, which then diffuse across the synaptic cleft and bind to receptors on the surface of the target cell.  
• Pheromones – Pheromones are signaling molecules used by multicellular organisms for various purposes. They typically act outside the body, facilitating communication between individuals of the same species and may be used to convey information such as indicating food supply, alerting against the presence of predators, or marking their territory. They also assist in mating and reproduction.