Paracrine signalling is when signal molecules are secreted into the extracellular fluid by signalling cells and the secreted molecules only affect neighbouring cells surrounding the signalling cell, acting as local mediators. Usually the signalling and target cells in paracrine signalling are of different cell types. When cells are able to bind the signal which it secretes or the cells of the same type bind the signal produce, this is called autocrine signalling. In order for the paracrine signals to act only close by, the secreted molecules must not diffuse too far; becasue of this they are often quickly taken up by target cells in the local environment, destroyed by extracellular enzymes, or immobilized by the extracellular matrix .
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2008) The Molecular Biology of the Cell, 5th edition, New York, Garland Science, Page 881