Is it true that we have a second brain in our stomach?

Society advances technologically by leaps and bounds, and with it, the knowledge and understanding of ourselves and the world around us.

Modern medicine and genetic study are disciplines that continually challenge preconceptions, and thanks to new investigations, organs of our own body that we thought we already knew are rediscovered with new and fascinating properties.

Such paths lead us to such bizarre statements as that "we have a second brain in our stomach." An alien concept for all, since we only know one nerve center in our body and this is located within the cranial cavity.

Like everything in the world of science and biology, we cannot state categorically that this postulation is entirely true. Do we have a second brain in our stomach? Yes and no. Read on to discover the correct answer to this question.

• Related article: "Parts of the Nervous System: anatomical structures and functions"

A second brain in the stomach: between myth and truth

It is clear that in order to understand the concepts to be covered in this opportunity, it is necessary that we first cement the functioning and general structures of both bodies involved.

1. About the brain

The brain is the nerve center of the nervous activity of all higher animals, including humans. It is responsible for thinking, memory, speech, language, reflexes, and body motor control.

In a typical brain slice, two well differentiated types of tissue can be seen: the white matter and the gray matter.. The first presents this "faded" color thanks to the axons of neurons, those terminations in the form of a "string of beads" responsible for transmitting the nerve impulse.

On the other hand, the gray matter corresponds to the agglutination of the neuronal bodies, that is, the somas.

In order not to get lost in the physiology of the lobes that make it up, we will limit ourselves to saying that the brain weighs about one and a half kilograms and its cortex contains roughly two trillion neurons. These figures speak for themselves about the utmost importance of this organ in the physiological framework of the human being.

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2. On the stomach

The stomach, for its part, corresponds to the dilated section of the digestive tract between the esophagus and the intestine. Together with the duodenum, it forms part of the proximal infradiaphragmatic portion of this system.

We could get lost in the physiology of this structural complex, but again, with just a few data, we are more than clear about the importance of the stomach for human functioning. This portion of the digestive tract is approximately 25 centimeters high and has a capacity of more than one liter of volume.

It presents a complex mucosa organized in a series of gastric folds, which are highly irrigated and innervated. In the end, the function of this section is food decomposition, so a wide contact with the rest of the body is essential.

As we have seen in these lines, the brain and stomach have little to do from a merely physiological point of view. Yes, both are an integral part of human functioning, but what makes some people claim that we have a second brain in our stomach?

Question of neurons

The answer lies in the neuronal composition of both structures. We have already said that there are around two trillion neurons in the cerebral cortex, a number with which it is certainly not possible to compete. Still, more or less 100 million neurons can be found in the stomach environment, that is, more than those present in the spine (or the same as those found in the brain of a cat).

It is because of this neuronal grouping that certain media affirm that the stomach is our second brain. But what is the function of such a neuronal grouping in the stomach? We will reveal it to you below.

1. Regulation of energy balance

Weight maintenance and body composition depend on hypothalamic (i.e., secreted by the hypothalamus) and non-hypothalamic factors, such as those produced in the intestinal tract that concerns us here.

The stomach alerts the central nervous system (CNS) of the nutritional status of the individual and their homeostasis energy through signals of distension and metabolic processes, that is, prereceptors and chemoreceptors. Various protein complexes such as insulin and leptin are generated in a modulated way in the gastrointestinal tract according to the individual state, which react with central neuropeptides by modulating appetite.

To summarize a bit the agglutination of terms shown previously, it could be said that the nervous system central nervous system and the stomach jointly participate in the modulation of appetite and energy expenditure in the short and medium term. Investigating these correlations is not trivial, since obesity is an increasingly worrisome pathology at the health level (it is present in 10% of the European population) and understanding the mechanisms of its emergence is one of the first steps to stop it.

2. Modulation of emotional state

Not everything is a question of neurons, for example, preliminary studies seem to indicate that there is a clear correlation between the emotional state of the individual and their gut microbiota.

We define the microbiota as the set of microorganisms (bacteria) associated in colonies that have evolved together with humans in a state of symbiosis. These, in the digestive tract, are responsible for promoting the synthesis of vitamins, digesting compounds of plant origin and promoting the specialization of the immune system, among others.

What was not so clear until relatively recently, is that the composition of the microbiota intestinal seems to modulate brain development and function and even the moods of the individual. For example, preliminary research has shown that there is a clear difference in the microbiota between patients with depression and people who do not suffer from this disorder.

Likewise, more and more studies indicate that possible correlations between autism spectrum disorders (ASD) and dysbiosis (imbalance of the microbiota) in the digestive tract. Of course, there is still a long way to go to fully understand these interactions.

In addition, 90% of the concentration of serotonin, a molecule that directly modulates human emotions, is found in the gastrointestinal tract. It is synthesized by neurons in the myenteric plexus to control intestinal secretions, motility, and sensations.

• You may be interested in: "Autism Spectrum Disorders: 10 symptoms and diagnosis"

3. Manifestation of stress

As we have seen, the stomach is an important factory of neurotransmitters, the engines of our mood. This portion of the digestive tract warns us, in different ways, that a situation of continuous stress over time is not sustainable at all.

Hormones such as cortisol (produced in the adrenal gland) promote gastric acid secretion, among other things. Prolonged exposure to stressful and anxious situations, therefore, cause a dysbiosis (imbalance in the intestinal microbiota) of the sufferer. This produces intestinal dysfunctions and less regeneration of the digestive mucosa, among other things.

All these mechanisms of action and many more can generate cramps, pain, gas, reflux and even promote the appearance of ulcers. Thus, the stomach warns us that we have to reduce the tensions of the routine if they get out of control.

Conclusions

As is obvious from the beginning, we can say that we do not have a second brain in the stomach. This denomination is the result of an enormous exercise in abstraction, since neuronal clumping in the stomach system works very differently than in the brain mass.

Even so, as we have seen, the stomach does modulate, in a certain way, moods, responses to stress and, of course, the appetite and energy balance of the individual.

Finally, we do not want to end this opportunity without calling for the search for real knowledge and the leakage of information. When talking about this type of topic, we cannot make sharp affirmations, and it is necessary to distrust who does it. No, "An imbalance of the microbiota does not cause autism", rather, "the microbiota between people within the spectrum autistic appears to be different from that of people without this disorder, so both could be correlated ”.

It is necessary to filter the information with caution and reserve, because in the world of physiological interactions within the human body there is still much to know and investigate.

Bibliographic references:

• Dinan, T. G., & Cryan, J. F. (2017). Brain – gut – microbiota axis — mood, metabolism and behavior. Nature Reviews Gastroenterology & Hepatology, 14 (2), 69-70.
• Kolb, B., & Whishaw, I. Q. (2006). Human neuropsychology. Panamerican Medical Ed.
• Martínez, J. A., & Solomon, A. (2006). Participation of the nervous system and the gastrointestinal tract in energy homeostasis. Journal of Medicine of the University of Navarra, 27-37.
• Navarro, A. N. D. R. AND. TO. (2009). Surgical anatomy of the stomach and duodenum. Digestive Surgery, 1-22.
• Ostrosky, F., & Neuropsychology, D. L. (2010). Brain development. Neurosciences, National Autonomous University, 1-10.
• Zacarías, M., Cadena, M., & Rivas, P. (2009). Structural modifications in the stomach and liver of Paralabrax maculatofasciatus (Steindacher, 1868) in situations of chronic stress. International Journal of Morphology, 27 (2), 425-433.