Which of the following is not the primary function of gut flora?
B i.e. Decreased proliferation of epithelial cellsGut (colonic) microflora synthesize sho chain fatty acids (SCFAs) by fermenting complex carbohydrate, resistant starches and other components of dietary fibers & mucin that escape digestion in upper git. They also produce vitamin K and biotin, detoxify xenobiotics, increase & maturate immunity, , preventing allergy and growth of pathogenic bacteria. They promote development of normal colonic epithelium and stimulate intestinal epithelial cell differentiation (ie increase not decrease proliferation of epithelial cells)Role of Colonic Microflora (Enteric Bacterial Ecosystem)Large intestine contains a unique biological ecosystem consisting of trillions of commensal (non pathogenic) bacteria that engage in a life long symbiotic relationship with their human host. This colonic ecosystem is established sholy after bih and remains remarkably stable unless disturbed by antibiotics. It is highly unusual relationship as other body compaments are largely sterile. It is involved inFermentation & Digestion of Complex Carbohydrate - Colonic bacteria metabolize meal components that are not digested by host enzymes and make their products available to the body fermentation. It provides advantage to the host in that the colonic bacteria are capable of performing metabolic reactions that do not take place in mammalian cells.- Carbohydrates that humans cannot digest without bacterial help include complex carbohydrate, resistant starches, dietary fibers, mucin (moucous) produced by gut and oligosaccharides / sugars that the body failed to digest /absorb d/t some pathology eg lactose in lactose intoleranceFormation of Sho Chain Fatty Acids (SCFAs)- Colonic bacteria form SCFAs by femanting carbohydrates (starches, fibers). SCFAs are 2-5 carbon weak acids with 80mmol/L average normal concentration in lumen. About 60% of this is acetate, 25% propionate and 15% butyrate.- SCFAs are absorbed & metabolized to make a significant contribution to total calory intake - butyrate is a critical energy source for colonocytes.- SCFAs exce a trophic effect on colonic epithelium cells. The colonic epithelium turns over rapidly even in health,limiting the genetic damage that might otherwise be caused by exposure to toxins in lumen. However, this also increases the risk of malignancy. The colonic flora ( SCFAs) is involved in promoting development of normal colonic epithelium and in stimulating its differentiated functions. Butyrate regulates the expression of specific gene in colonic epithelial cells and may suppress the development of a malignant phenotype. Expression of SMCT1 (sodium monocarboxylate transpoers 1) eg SLC5A8 may be reduced in colon cancers, thereby reducing butyrate uptake - which may contribute to malignant transformation. So SCFAs increase the growth of intestinal epithelial cells and control their proliferation & differentiation (ie promoting normal development & stimulating differentiation)- SCFAs combat inflammation (prevent inflammatory bowel disease) maintain acid -base equilibrium (absorbed in pa by exchange for H+) and promote absorption of Na+, Mg++, Ca+ and Fe++Metabolism of Exogenous & Endogenous Substances- Gut flora forms secondary bile acids and deconjugate any bile acids that have escaped uptake in terminal ileum- Contribute to formation of intestinal gas.Detoxification- Detoxify xenobiotics (eg drugs) & dietary carcinogen (but may also generate toxic or carcinogenic compounds from dietary substrates.Antimicrobial- Gut flora limits the growth & invasion of pathogenic microorganisms by1) Functioning as a physical barrier to prevent attachment of pathogens.2) Forming microbicidal substances,3) Triggering gene expression in epithelium that counteracts the adverse effects of pathogensPrevent Allergy & Provide Immunity- Gut flora is not essential for life as animals raised in germ free conditions apparently develop normally. However, in these animals the mucosal immunity is immature and intestinal epithelial cells differentiate more slowlyQ- Colonic microflora trains immune system preventing allergy & providing immunity.Synthesis of Vitamin K & BiotinSubstrateEnzymesProductsDispositionEndogenous SubstratesUreaUreaseAmmoniaPassive absoionor excretion asammoniumBilirubinReductasesUrobilinogenStercobilinsPassivereabsorptionExcretedPrimary bileDehydroxylasSecondaryPassiveacidsesbile acidsreabsorptionConjugated bileDeconjugasesUnconjugatePassiveacids (primaryor secondary) d bile acidsreabsorptionExogenous SubstrateFiberGlycosidasesSho-chainfatty acidsHydrogen,CO2 andmethaneActive absorptionExcreted in breathor flatusAmino acidsDecarboxylasAmmoniaReabsorbed or es andandexcreted deaminasesbicarbonate(ammonia) asammoniumCysteine,methionineSulfatasesHydrogensulfideExcreted in flatu
Synthesis of sho chain fatty acids
Decreased proliferation of epithelial cells
Production of vit. K
Fermentation of mucin