What is the Difference Between Autocrine and Paracrine

The main difference between autocrine and paracrine is that the autocrine factors act on the cells which produce them whereas the paracrine factors act on the cells that are in close proximity to the cells that produce them. 

Autocrine and paracrine are two terms used to describe various factors that are a part of the cell signaling mechanisms.  Furthermore, the growth factors which stimulate cell division is an example of autocrine factors while cytokines, which cause inflammatory responses, and neurotransmitters released into the synapse are some examples of paracrine factors. 

Key Areas Covered 

1. What is Autocrine
     – Definition, Signaling Molecules, Examples
2. What is Paracrine
     – Definition, Signaling Molecules, Examples
3. What are the Similarities Between Autocrine and Paracrine
     – Outline of Common Features
4. What is the Difference Between Autocrine and Paracrine
     – Comparison of Key Differences

Key Terms 

Autocrine, Cytokines, Interleukins, Neurotransmitters, Paracrine

What is Autocrine 

Autocrine is the term used to describe a type of cell signaling molecules that bind to the cells of production. This means that the target cell of these signaling molecules is the same cell from which they are produced. Therefore, autocrine signaling helps the cells to send signals to itself. During early development, autocrine signaling ensures the differentiation of cells into the correct tissue.  

Figure 1: Types of Cell Signaling

In addition, autocrine actors such as interleukins play a key role in the development of inflammatory signals and pain sensation. Interferons are a type of cytokines which can act as autocrine signals in virus-infected cells. They induce programmed cell death of the virus-infected cell.  

What is Paracrine 

Paracrine is the term used to describe another type of cell signaling molecules which acts on the cells that are in close proximity to the cells of production. This means the target cells are nearby cells and the diffusion of paracrine molecules occurs through the extracellular matrix. Due to the short distance between the target and the cells of production, paracrine signaling takes a short time to reach to the target when compared to the endocrine signaling, which diffuses through the bloodstream. Moreover, since the paracrine signal has to be localized, the paracrine signaling molecules are quickly degraded by enzymes.  

Figure 2: Neurotransmitters in the Synaptic Gap

The most common example of paracrine signals is the signal transmission through the synaptic gap. Neurotransmitters are the paracrine signaling molecules involved here to transmit nerve impulses from the pre-synaptic neuron to the post-synaptic neuron.  

Similarities Between Autocrine and Paracrine 

• Autocrine and paracrine are two types of cell signaling mechanisms. 
• Also, small protein molecules serve as the signaling molecules in both. 

Difference Between Autocrine and Paracrine 

Definition 

Autocrine means “relating to a cell-produced substance that has an effect on the cell by which it is secreted” while paracrine means “relating to a hormone which has effect only in the vicinity of the gland secreting it”.  This explains the basic difference between autocrine and paracrine.

Types of Signaling Molecules 

Another difference between autocrine and paracrine is that the cytokines and growth factors are the main types of signaling molecules involved in autocrine signaling while neurotransmitters and hormones are involved in paracrine signaling. 

Target 

The target of the autocrine signaling molecules is the cells of production while the target of the paracrine signaling is the cells in the close proximity. This is the major difference between autocrine and paracrine.

Examples 

Cell differentiation in the early embryo occurs through autocrine signaling while signal transmission through the synaptic gap occurs through paracrine signaling. 

Conclusion 

Autocrine signaling stimulates the cells of production while paracrine signaling stimulates the cells in the close proximity. Cytokines and growth factors are the autocrine signaling molecules while neurotransmitters are paracrine signaling molecules. The main difference between autocrine and paracrine is their mechanism of action. 

Reference:

1. “Types of Signals.” Lumen, Lumen Learning, Available Here

Image Courtesy:

1. “Cell signalling” By Doublethink – Own work (Public Domain) via Commons Wikimedia  
2. “Figure 09 01 02” By CNX OpenStax –  (CC BY 4.0) via Commons Wikimedia