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The human gut is often referred to as the "second brain," it is the only organ having own independent nervous system composed of a network of 100 million neurons embedded in the gut wall. The microbiome is a collection of microorganisms in a particular environment in the body. People have skin microbiome, an oral microbiome, and also have a gut microbiome and it includes the life of bacteria, fungi, viruses, protozoa, as well as all of their genetic materials. As far as it is known the gut microbiome weighs about 2 kilograms. When we refer to the gut microbiome, we will consider all of the trillions of bacteria residing in the gastrointestinal tract. Within the last years there is more research about the possible connection between the gut and the immune function, metabolism, hormone regulation, behavior and mental health.

The gut microbiome and the brain communicate through the microbiota-gut-brain axis, though the vagus nerve that has an anti-inflammatory pathway. The communication process works both ways, where the gut microbiome can affect the brain and the brain can affect the gut microbiome. Stress is known as a major factor for the suppression of vagus nerve function and this can result in damage to the GI tract and microbiome. The vagus is the longest cranial nerve in the body – starting at the base of the brain and running down your neck into the body. This is often observed in cases of depression, anxiety and mood disorders in general. The brain can also influence significantly the gut bacteria and even some stress can harm the microbial balance in the gut, making the individual experiencing it less capable of responding to stressful events.

When we are born everyone of us have his gut sterile. As the years goes by, everyone's gut develops a very diverse through the different bacterial species, determined by genetics as well as by the bacteria are living around us. The 100 trillion microbes that have established their home inside the GI tract are more than important to our physical and mental health. Gut bacteria are functioning as main mechanisms for the regulation of the digestion and metabolism. As well as they extract and produce certain vitamins and other nutrients by taking the building blocks and the composition elements from the food that we are eating.

The health of the Gut microbiome is directly related to the strength and the capabilities of the body's immune system. The microorganisms can build and maintain the gut wall and help it perform its most important function to protect the body from outside invaders and pathogens. The beneficial bacteria in the gut are confronting the harmful microbes by producing anti-microbial chemicals.

How we feel emotionally is directly linked to our gut. When we have a certain feeling of worry or nervousness, we experience physical sensations in our stomach. And in times of stressful events, we can drastically change our appetite and necessity for food from junk food cravings to absolutely NO appetite.

The key link for transferring our emotional feelings – messages from the brain down to the gut is the upper mentioned vagus nerve. We can refer to the vagus nerve as the physical representation of the mind-body connection.

The autonomic nervous system is an unconscious and we even do not think about its responsibilities. It is automatic system that manages our essential bodily functions from our heartbeat, breathing, digestion to managing the waste. It is divided into two sub systems known as the sympathetic and parasympathetic nervous systems.

When we are stressed out through the “fight or flight” response the sympathetic nervous system starts providing mental alertness and the energy to escape or defend ourselves. But when we are relaxed the parasympathetic nervous system is active in the state of “rest and digest”.

The balance between our sympathetic and parasympathetic nervous systems has a huge impact on physical and mental health.

Chronic stress can lead to exhaustion of the parasympathetic nervous system being drowned out by a hyperactive sympathetic system. This can be seen in high blood pressure and cardiovascular diseases, type two diabetes and obesity.

The feeling in our Gut

Our gut stores an independent “mini-brain” that is a complex network of neurons called the enteric nervous system. The parasympathetic nervous system sends commands to the gut if it can start digesting food. But also, there is one more important component – the Ghrelin hormone, also known as the “hunger hormone”. Ghrelin is produced in the gut and it travels through the bloodstream to the brain, where it sends commands to the brain to become hungry and start seeking for good food. Not just that, it also affects the sleep-wake cycle, reward-seeking behavior and carbohydrate metabolism. It is secreted when the stomach is empty and when its levels are high, the hungrier person becomes. When its levels are low the person do not need much food and eats less.

The more we know the gut-brain axis the more we can understand the complex communication link between the brain and the enteric nervous system. After we explored this connection in a bit more detail we can return to the mini microorganism world living inside our gut.

They can increase the neuroplasticity in the brain and this is linked to mood and the memory centre – the hippocampus. Gut bacteria also produce hundreds of neurochemicals that the brain uses for the regulation of numerous physiological and mental processes such as learning, memory and mood. Gut bacteria is capable of producing huge percent of the body's supply of serotonin which is linked to the mood and also the GI activity.

Our emotions can manifest in our digestive health and this often linked to inflammation. Currently there is a lot of research focused on observation of the connection between inflammation and depression and anxiety, chronic inflammation and and mental health disorders.

According to research it is possible that the gut microbiome starts influencing human behavior very soon after birth. It can prepare some aspects of brain development, such as its response to stress. Just as gut bacteria affect the brain, the brain can also influence the gut microbiome and numerous studies have shown that psychological stress suppresses beneficial bacteria.


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