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How Are Our Brain and Gastrointestinal System Connected?

The intricacies of how our body works are still being explored by some of the world’s top scientists. While our brain and our gut have their own important roles to play in our body, they also have a complex relationship and rely upon one another for many of their jobs. By better understanding this connection, we can feel more in tune with ourselves and understand why changes within our body can occur; like how changes in our emotions or stress levels can affect our stomach and bowels. 

Below we have broken down the main pathways our body uses to talk between our brain and our gut. 


The Gut-Brain Axis

There is a two-way communication path between the gastrointestinal tract and the brain. Your gastrointestinal tract is lined with nerves that make up the enteric nervous system (ENS) – which regulates the function of your gastrointestinal system (like telling it when to move food along or secrete different substances). The ENS can talk to the brain through various different pathways; three main pathways are the vagus nerve, the gut microbiota and hormones.



The Vagus Nerve

The vagus nerve runs from your brain to your large intestine. It plays a key part in connecting our gut and our brain, and has a range of important functions in our body. Some of these include:

  • It carries sensory information from the gastrointestinal tract to the brain – for example, about how full our gut is, the nutrients in our gut and any pain or discomfort.
  • It transmits signals from the gut to different regions of the brain to regulate automatic processes and higher cognitive processes.
  • Coordinating gut movements, secretion and blood flow to help digest our food. 

The vagus nerve has a lot more roles within the body. For example, when the vagus nerve is stimulated, it can help regulate our stress response through neurotransmitters that influence emotions and cognitive processes, assisting us to calm. As well as that, it helps with our breathing, reflexes and heart rate. 


The Gut Microbiota

Within all of our digestive systems (mainly within the large intestine) are complex microorganisms that help maintain our health and keep our body working. These microorganisms include bacteria, viruses, fungi, and other tiny organisms. There are trillions of them!

The gut microbiota can produce metabolites and chemicals that can directly affect the brain, like by influencing our behaviour, mood, and cognition. They also produce neurotransmitters and hormones that can impact the communication between the gut and brain.



When hormones like serotonin, dopamine and norepinephrine are released into the body, your brain and gut can both be affected. 

Let’s take the hormone serotonin for example. 90% of serotonin is created and released in the gut, but it’s also released from the brain and parts of the central nervous system. Serotonin is the major regulator of gut motility (moving the muscles of our gastrointestinal tract to help digest food), nausea and gut secretion. It also plays a big role in regulating our mood, sleep and the stress response.

When our body experiences stress, it can affect serotonin levels, its release, and how our body absorbs it! Stress can increase the amount of serotonin created in our gut, while decreasing the amount of serotonin in other areas. Increased serotonin may be associated with diarrhoea. Low levels of serotonin have also been associated with depression and anxiety disorders. Even just this one hormone, can affect so many different areas of our body!


The gut-brain connection is a complex and important part of our bodies. In an upcoming blog post, we will learn more about this connection by delving into how anxiety and stress can have big effects on your gut. 


SIENNA SMILEY (Occupational Therapist).


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