Question

To keep their action local, paracrine signal molecules must be prevented from straying too far from their points of origin. Suggest different ways by which this could be accomplished. Explain your answer

Answer 1

There are four types of signalling pathways in our body. They are endocrine, autocrine, paracrine and direct signalling. The main difference between them is the distance travelled by the signal to reach target cell.

What is a paracrine signaling?
Signals that must result in a sudden response is done by paracrine signaling. It is happening in the nearby cells. The signals moves to the adjacent cell by diffusion through the extracellular matrix.
The response produced by paracrine is fast but last for very less time. For example, a signal to takeoff the hand from the stove.

Citing an example of a signal passage accross synapse between nerve cells. The nerve has a cell body, signal receiving dendrites, long axon , synapses which are near the adjacent nerve cell etc. The signal passes through nerve and it is transmitted to the next cell by diffusion as a chemical signal called neurotransmitters. It act as ligand and bind to receptors. This changes the electro chemical potential of receiving cell. Thus the response takes place. The neurotransmitters are removed by cell or is cleaved quickly by enzymes so that the receiving cell get back to its normal condition.

How the signaling molecules are precented from staying too far from point of origin?

In order to keep the response localized, paracrine ligand molecules are,
1. Normally quickly degraded by extracellular enzymes.
2. Rapidly taken up by the neighboring target cell.
3. Immobilized by the ECM, often to be released at a later time.

Removing the signals will reestablish the concentration gradient for the signal, allowing them to quickly diffuse through the intracellular space if released again.