Everything is connected.
No, this won't be an essay on meditation and the Oneness of Being. It's about the various organ systems in the body and how, the more we learn, the more we discover they're all connected and communicating with each other.
Physiology is usually taught around different systems: circulatory system, nervous system, skelatomuscular system, with individual organs within the systems. Of course you know they're interrelated, but one tends to think of them in isolation. The pancreas produces insulin, the liver produces bile, the stomach produces acid, and so forth.
However, as science progresses and we're able to detect things in tiny amounts, not just the large amounts that we could detect in the past, we're learning how complex it all is. For example, insulin is produced mostly by the beta cells in the pancreas. But smaller amounts of insulin can be produced by the thymus, liver, and fat and probably brain.
And various systems interact in ways that one might not think of until someone stumbles on them.
For example, a recent paper shows that nerve growth factor (NGF), which is known to regulate the development of nerve cells, also helps to tell beta cells to release insulin. High blood glucose levels cause NGF to be released from pancreatic blood vessels, and the NGF then tells the beta cells to release insulin.
Another paper shows that the immune sytem uses gut bacteria to control glucose metabolism. An immune system molecule called interferon helps to fight infections. But a decrease in interferon-gamma can improve glucose metabolism. And when these interferon levels decrease, levels of a specific species of bacteria increase. The researchers think the bacteria are providing the link between the immune system and blood glucose control.
Another one shows that gut bacteria can block the loss of appetite that often accompanies a stomach bug. They do this to promote the bacteria's transmission to other hosts.
Another paper shows that cutting the nerves to the kidneys reduces insulin resistance. It seems that the liver and the kidneys communicate to set glucose levels, and cutting the nerves to the kidneys makes the liver more insulin sensitive. One problem in type 2 diabetes is that because of liver insulin resistance the liver keeps pouring out glucose even when the level is already too high. Kidney function in the dogs used in the study remained normal.
Finally, a paper shows that a brain hormone triggers fat burning in the gut. This hormone, called tachykinin, was identified 80 years ago as a peptide that triggered muscle contractions in pig intestines. It seems that this hormone is released in the brain in response to the serotonin level. Serotonin is related to mood, and low serotonin levels can cause depression. Also, some of the side effects of the drug metformin seem to be mediated by binding to serotonin receptors in the gut.
In this case, sensory cues such as food availability cause the brain to release serotonin. This tells certain neurons to release tachykinin. The tachykinin then activates a receptor in intestinal cells, and the intestines begin to burn fat.
These are just a few examples of how one organ affects another, and even our gut bacteria are involved in the communication.
There's more and more evidence that gut bacteria control a lot of things
in the body. Wouldn't it be wonderful if some species could produce an
insulin-like molecule that was resistant to degradation in the gut? No
evidence for that. I'm just dreaming.
Understanding all these interactions is not easy, but it means that everything in our bodies is important. We can't focus only on blood glucose levels and ignore our mental health or our intake of healthy foods that don't affect blood glucose directly but may nurture the good gut bacteria.
Our bodies know how to communicate in ways we don't yet understand. Our job is to be kind to our body so it can do its job as best it can. Enjoy life. Enjoy your friends. Enjoy your food. And stay healthy for a long, long time.