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According to a recent National Institutes of Health (NIH) estimate, 90% of cells in the human body are bacterial, fungal, or otherwise non-human.
We are never truly alone. On our skin, in our gums, and in our guts live 100 trillion organisms, altogether known as the microbiome. These beasties comprise 90% of the cells of our bodies, though these cells are so tiny in size that it appears our own human cells predominate. It is only recently that we have begun to study these organisms with any depth. Most of them live within the gut, and cannot be cultured, and only with the advent of advanced genetic testing have we been able to have a better understanding of the variety and numbers of microbes we’re dealing with. They are Bacteria, Archaea (link is external), and even some eukariotic (link is external) parasites, protozoans, and fungi.
What do they have to do with psychiatry? It turns out way more than we might have suspected. The gut and brain have a steady ability to communicate via the nervous system, hormones, and the immune system. Some of the microbiome can release neurotransmitters, just like our own neurons do, speaking to the brain in its own language via the vagus nerve.
To have a full understanding of how the whole gut-brain connection works, you need robust knowledge of endocrinology, immunology, pathology, and neurology, which is a bit beyond the scope of a blog article. However, to break it down to simplistic terms, here are the basic links:
1) The body responds to stress (mental or physical) via the hypothalamic-pituitary-adrenal axis. For example, if you are eating lunch and a lion jumps into the middle of your picnic table, your “fight or flight” system is fired into full gear, your heart pounds, your pupils dilate, your hair stands on end, natural steroids and adrenaline flood your system to strengthen your muscles and give you an extra burst of speed. Even your platelets change shape so they are more sticky, leaving you less likely to bleed out if you are attacked. Naturally, our bodies have negative feedback that can tone down the fight or flight response once the danger is past (assuming you survive). Under conditions of chronic stress, however, mental or physical, the feedback tends to get messed up, leading to symptoms of chronic stress (which includes mental issues such as anxiety or clinical depression, but also physical problems such as chronic gut problems, headaches, high blood pressure, etc.). What does all of that have to do with the gut?
2) While the hormonal system that regulates fight-or-flight, rest-and-recovery, and everything in between is easy to conceptualize, the second underlying system, the immune system, is far more complex and works at a cellular level. Our bodies aren’t particularly sophisticated when it comes to facing off against stress. Our stress response doesn’t readily distinguish between mental and physical distress; your heart pounds and you tremble with anxiety when you are in an uncomfortable meeting with your boss, when such a reaction is not helpful in that situation, though it might have helped with the lion. And not only to we respond to the tough day on the job with a hormonal response, but also an immunological one. When our body is under stress, it releases what are called inflammatory cytokines, little chemical messengers that bring a certain part of our immune system into high alert. In a sense, our body reacts to all stress as if it were an infection, and to chronic stress as if it were a chronic infection.* Now the immune system works wonders and inflammation saves your life nearly every day from all the pathogens out there like the flu and strep, but chronic levels of inflammatory response also lead to all sorts of chronic disease, for example depressive disorders, high blood pressure, atherosclerosis, autoimmune diseases such as ulcerative colitis and multiple sclerosis. Immune system activation can also determine whether or not we develop cancer. Where does the gut get involved? Well, it turns out the gut microbiome plays a key role in regulating our immune response. Thus the make-up of our gut microbiome could make the difference as to whether we are sick or well, both mentally and physically.
3) Animal and human studies support the theory that pathogenic bacteria in the gut, such as C. Difficile, or in certain circumstances, H. Pylori, lead to human disease, and not just the obvious direct illnesses, pseudomembranous colitis (link is external)and ulcers. These bacteria also interact with the immune system in the gut to cause the release of inflammatory cytokines, stress steroids, and a systemic stress response (similar in most ways to the lion attack). Some of the responses of the gut even have an effect on our pain response…yes, people with certain unfavorable gut bacteria might be more sensitive to pain than others.
Different kinds of bacteria that live inside the gut can help spur obesity or protect against it, according to new research from scientists at Washington University in St. Louis.
originally posted by: Utnapisjtim
mpkb.org...
According to a recent National Institutes of Health (NIH) estimate, 90% of cells in the human body are bacterial, fungal, or otherwise non-human.
Humans are meat robots built round a metal skeleton packed with flesh and fats— full of bacteria and fungus. I think it's safe to assume that there are likely to be more bacteria cells on any given part of your body than there are on a regularly washed toilet seat.
originally posted by: ketsuko
we need our bugs to stay healthy.