As the embryo develops past the eight cell stage, the cells become different from one another due to cell-cell communication.

Cellular communication ensures regulation of biological processes via various types of signaling that allow chemicals to travel target sites to elicit a response. The ability of cells to communicate through chemical signals originated in single cells and was essential for the evolution of multicellular organisms. In multicellular organisms, cells send and receive chemical messages to coordinate the actions of distant organs, tissues, and cells. Single-celled organisms, like yeast and bacteria, communicate with each other to aid in mating and coordination. Cellular communication has developed as a means to communicate with the environment, produce biological changes, and, if necessary, ensure survival.

The major types of signaling mechanisms that occur in multicellular organisms are paracrine, endocrine, autocrine, and direct signaling. The main difference between the different categories of signaling is the distance that the signal travels through the organism to reach the target cell. 

Paracrine signals act on cells in the local area. Endocrine signals involve secreted hormones that travel through the bloodstream to a distant target tissue. Autocrine signals act on the same cell that secreted the signal in the first place. Finally, direct signaling can occur by transferring signaling molecules across gap junctions between neighboring cells.

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Key Points

• Cells communicate via various types of signaling that allow chemicals to travel through target sites to elicit a response.

• Autocrine signals are produced by signaling cells that can also bind to the ligand that is released, which means the signaling cell and the target cell can be the same or a similar cell.

• Paracrine signaling occurs between local cells where the signals elicit quick responses and last only a short amount of time due to the degradation of the paracrine ligands.

• Endocrine signaling occurs between distant cells and is mediated by hormones released from specific endocrine cells that travel to target cells, producing a slower, long-lasting response.

• Direct signaling can occur by transferring signaling molecules across gap junctions between neighboring cells.

Key Terms

cellular communication: cell communication is the process by which a cell detects and responds to signals in its environment

endocrine signaling: signals from distant cells that originate from endocrine cells, usually producing a slow response, but having a long-lasting effect

autocrine signaling: produced by signaling cells that can also bind to the ligand that is released: the signaling cell and the target cell can be the same or a similar cell (prefix auto- means self)

paracrine signaling: a form of cell signaling in which the target cell is near (para = near) the signal-releasing cell