By Elizabeth-Grace Warrior
Our bodies are capable of amazing feats and are truly complex organisms. Often regarded as the mastermind of all our functions, the brain is often thought of as the singular organ that governs our body and dictates our activities. Unbeknownst to the majority of us, in relatively recent years it has come to light that in fact, our bodies have two brains. The gut, also known as our ‘second brain’ is a complex system full of mysteries yet to be discovered.
Going further back than just a few years ago, and longer than modern medicine, there has been an idea that food could be the cause and cure of our ailments. Hippocrates famously said ‘All disease starts in the gut’, clearly he was onto something as the ideas he speculated all the way in 400 BC, are now coming into light as recent scientific developments. This raises the question, how does the gut influence the brain and body, and vice versa?
The gut and the brain are closely linked in a two-way communication system known as the gut-brain axis, the centre of their transmissions. This system facilitates the bidirectional flow of information between our gut and brain, hence allowing a constant stream of information to be exchanged between these two organs, including everything from our mood and emotions to our digestive process. Common examples of this could be when we are experiencing stress or anxiety with which our stomach responds with butterflies or discomfort. The gut-brain axis is essential for maintaining homeostasis within our bodies and unbeknownst to us plays a crucial role in our everyday life.
At the very core of the gut-brain axis lies the vagus nerve which extends all the way from our brainstem to our abdomen and acts as a pathway to transmitting signals between the brain and the gut. Essentially, the GB axis transforms information via the vagus nerve from our food, to our feelings. Once eaten, digested food particles enter our small intestine which is lined with millions of villi. A single layer of epithelial cells lines the inside of each villus and when you start to zoom in from here, the interesting things occur as one cell’s function is oddly distinct. The enteroendocrine cell, which serves as our gut's gatekeeper, has been shown (by Duke University) to synapse with nerves, including the vagus nerve, in addition to communicating through hormones. Enteroendocrine cells that synapse with nerves can also be referred to as neuropod cells. Little electrical pulses are created inside neuropod cells in response to stimuli, and these pulses are then sent via synapses to the vagus nerve's efferent neuron. Following this, the vagus neurons pass this information to the brain, hence linking signals from our gut to the brain. This connection enables food in the gut to influence brain function within seconds. Similarly, the brain can also release neurotransmitters down the vagus nerve, affecting our digestion. This has formed the basis of therapies aimed at treating disorders related to altered gut-brain communication.
Another integral part of the gut-brain connection is also deeply rooted in another plexus, the enteric nervous system. The ENS is a complex web of neurons embedded in the walls of the gastrointestinal tract. This highly specialised network of neurons that makes up the enteric nervous system (ENS) is sometimes called the "second brain" because of its amazing capacity to manage the many complicated activities of the gut autonomously. The ENS, which extends from the oesophagus to the rectum, is essential for food digestion, absorption, and peristalsis in addition to keeping the gut homeostasis. It can continue to function even if the connection to the central nervous system (CNS) is lost as it functions independently and communicates with the CNS as needed.
By means of the vagus nerve and the sympathetic nervous system, the ENS exchanges information about the condition of the gastrointestinal tract with the central nervous system (CNS). Due to this two-way communication, the CNS is able to affect gastrointestinal function as necessary, such as during the "fight or flight" reaction, which prevents digestion while under stress. It also plays a vital part in regulating our mood and well-being; this ‘second brain’ produces loads of the same neurotransmitters as the ones found in our brains, including serotonin, dopamine, and gamma-aminobutyric acid. “More than 90% of the body's serotonin lies in the gut, as well as about 50% of the body's dopamine”. These neurotransmitters are all closely associated with mood and emotions, revealing how the ENS links to the brain.
Thoughts on the gut-brain connection have linked back to ancient times, and it’s truly impressive what scientists have been able to accomplish over the last few decades. These groundbreaking discoveries on our ‘two brains’ have opened the door to therapies that will enable us to take a clearer approach to treating illnesses related to the gut and our brain.
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