Abstract
Nearly all animals possess a digestive tract (the exception being parasites that live within their host’s tissues or digestive tracts) and in nearly all cases this consists of an open tube with flow of contents from one end (mouth or stoma) to the other (anus). Since the animal is ingesting food from its environment, it is also ingesting all of the microbes that are associated with the food, along with those from the immediate environment. This means that, although the gut within a foetus developing in the uterus is normally sterile, the adult gut has no chance of being sterile. It will inevitably become colonised by micro-organisms that are able to take advantage of the readily available sources of energy to be found in the gut.
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Notes
- 1.
Acids dissociate readily to release a hydrogen ion (H+). When acetic acid releases H+, it becomes the ‘acetate ’ anion (A−). Both the dissociated and non-dissociated forms exist together, with their proportions depending on the prevailing pH. For convenience we will generally refer to the anion (formate , acetate , lactate etc.) in this book.
- 2.
The pH is a number that represents the acidity or alkalinity of the environment on a scale of 0 (most acidic) to 14 (most alkaline (or basic)). pH 7 is defined as neutral. pH is determined by the concentration of hydrogen ions; specifically, pH is the negative logarithm of the hydrogen ion concentration (e.g. a H+ concentration of 10−5 M is pH 5).
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Flint, H.J. (2020). The Gut Microbiome: Essential Symbionts or Unwelcome Guests?. In: Why Gut Microbes Matter. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-43246-1_2
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