Cells communicate with each other via different types of signalling, allowing chemicals to travel to target sites. There are four main types of signalling: Paracrine, Endocrine, Autocrine and Direct.
Paracrine signalling exists between local cells. Signals evoke fast responses and last for a very limited amount of time, the reason being the degradation of the paracrine ligands.
Endocrine signalling happens between distant cells and is orchestrated by hormones. These hormones are secreted by specific endocrine cells, and they travel to the target cell. They produce slow, long-lasting response.
Autocrine signals come from signalling cells, able to bind to the ligand that is released, meaning the signalling and target cells can be either a similar or the same cell.
The Direct signalling occurs via transferring signalling molecules across gap junctions between neighbouring cells.