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synergy · 2
A large share of the body's immune cells are stationed in the gut wall (in gut lymphoid tissue such as Peyer's patches), where they learn to tell food, resident bacteria and pathogens apart. When the gut barrier is damaged, bacterial components may enter the blood and trigger low-grade inflammation throughout the body.
The gum pocket is another territory guarded by neutrophils: once a keystone pathogen such as Porphyromonas gingivalis throws the immune defense into disarray, what leaks out with the inflammation becomes food for the bacteria. It is the same kind of loop as some gut bacteria profiting from inflammation.
cofactor · 1
H. pylori does not live soaking in stomach acid; it burrows under the mucus layer and lives against the surface of the stomach lining, where the pH is close to neutral, one of the few mild spots in the stomach. To understand this move, you first need to know how stomach acid is made and how the mucus barrier works.
regulates · 9
The liver secretes bile every day to help the gut digest fat; most bile acids are reabsorbed at the end of the small intestine and, through receptors such as FXR, send signals back to the liver that regulate bile-acid and fat metabolism. In metabolic dysfunction-associated steatotic liver disease (MASLD, formerly called non-alcoholic fatty liver disease), this gut-liver loop can be disturbed and is thought to be one factor that makes the disease worse.
The gut and brain talk in both directions. The gut has its own large nerve network (the enteric nervous system), through which, along with the vagus nerve, the brain adjusts gut movement; in animal studies, the short-chain fatty acids made when gut bacteria ferment fiber can influence the brain through routes such as the vagus nerve. Most of the body's serotonin is made in the gut, but it cannot enter the brain and acts mainly in the gut.
The gut releases many hormones: GLP-1, released after eating, promotes insulin release and curbs appetite; GIP also promotes insulin release; and ghrelin from the stomach makes you feel hungry when it is empty. The way gut hormones amplify the insulin response after a meal (the incretin effect) is the physiological basis of GLP-1 receptor agonist drugs.
↔GERD
Gastroesophageal reflux disease (GERD) is a valve at the bottom of the esophagus that does not close properly, plus slow stomach emptying, weaker clearing of refluxed contents from the esophagus and weaker mucosal defenses. Care usually starts with lifestyle changes (losing weight, raising the head of the bed, avoiding trigger foods) and then acid-suppressing drugs; in erosive esophagitis, Laine 2023 found vonoprazan's 8-week healing rate noninferior to lansoprazole's (92.9% vs 84.6%). For people with long-standing reflux and 3 or more additional risk factors, the ACG 2022 guideline conditionally suggests one screening endoscopy for Barrett's esophagus.
Venous blood from the gut flows straight into the liver through the portal vein, so the products of gut bacteria (endotoxin, short-chain fatty acids, secondary bile acids) are important signals for liver metabolism and inflammation. One explanation holds that once fat has built up in the liver, further hits such as endotoxin from the gut may push fatty liver on to metabolic dysfunction-associated steatohepatitis (MASH).
The small intestine absorbs glucose through a transporter called SGLT1, which pulls glucose into gut cells together with sodium; when a single sugar is taken in too fast (at around 60–70 g an hour), that door saturates. Fructose uses a different door, GLUT5, so adding fructose once the first door is full lets more sugar be absorbed and used.
↔IBS
Irritable bowel syndrome (IBS) is not just a bowel problem; it involves the two-way link between gut and brain, and about 80% of the vagus nerve's fibers carry signals from the gut up to the brain. That figure is a fiber count, not a measure of signal traffic. So looking for a lesion in the bowel alone usually finds nothing and fixes nothing.
In celiac disease, after the enzyme tissue transglutaminase modifies (deamidates) gliadin from gluten, the immune system attacks it, the damage lands on the villi of the small intestine, and the absorptive surface is worn flat. Diagnosis requires blood tests and a biopsy, and the treatment is a strict gluten-free diet.
←IBD
The inflammation of Crohn's disease can extend through the full thickness of the bowel wall and can appear in any part of the digestive tract, while ulcerative colitis stays in the lining of the colon. Which part is affected decides which deficiencies are likely: when the end of the ileum is involved, for example, vitamin B12 absorption is more likely to suffer.