4.1 Cell Communication

The cells in your body communicate in many different ways. Cells must communicate with each other and the environment in order to complete tasks. They communicate through chemical signals. These signals are usually proteins. Multicellular organisms have trillions of cells that communicate in the following ways. 

Juxtacrine Signaling

Direct contact is also called juxtacrine signaling. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the plasmodesmata connect one plant cell to another. In animal cells, gap junctions directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules. 

Memory Tip: Think of direct contact like a handshake because both people must have direct contact with each other during a handshake!

Image courtesy of Giphy.

Paracrine Signaling

Another way that cells communicate is through paracrine signaling. 

Paracrine signaling is communication over short distances. Cell sends out signals to nearby cells which causes a change in the behavior of nearby cells. An example of paracrine signaling is contracting muscles. Chemical signals are sent from the nerve to the muscle. This causes the response of changes in the behavior of muscle so that the muscle contracts. Another example would be synaptic signaling involves a synapse which is the gap between 2 nerve cells. Signaling occurs when a neuron releases a neurotransmitter. Then, the neurotransmitter moves across the synapse. After it reaches the end of the gap, the neurotransmitter stimulates the adjacent neuron to fire.

Memory Tip: Think of paracrine signaling as crossing the street. Crossing the street is a short distance and helps me remember that paracrine signaling is between nearby cells. Takes the “right down the street” phrase into a new perspective!

Image courtesy of Giphy.

Autocrine Signaling

Autocrine signaling is essentially a cell sending chemical messages to itself. It would involve the cell releasing a chemical and then having a receptor that receives this message. An example of this would be cancer cells. Cancer cells release their own growth hormones so that they can keep on growing, instead of relying on growth hormones from the host organism. In this way, the cancer cells can keep growing faster and more efficiently. 

Memory Tip: "Auto" means self, so autocrine signaling must be signaling to yourself. Think of other words that involve the root "auto" like autopilot. 

Endocrine Signaling

Here, we have endocrine signaling, which is signaling another cell by sending the ligand through the bloodstream, perhaps to a different organ cell. This is different from paracrine signaling because that only involved sending it off to a cell nearby. Endocrine signaling is like sending a something to a different country. It's much more far away, so the ligand is also equipped to have a longer lifespan. An example of this would be the pancreas cells releasing insulin when blood sugar levels are too high. This insulin is then received by the liver cell and glucose is converted to glycogen as a response. 

Memory Tip: Think of this as sending a letter or package to a different country so your letter or package must travel by water to reach its destination. 

Check out the AP Bio Unit 4 Replays or watch the 2021 Unit 4 Cram