The Small Intestine


Alongside the digestive secretions from the Pancreas & Gall Bladder, the lining of the Duodenum produces brush border enzymes, that add to the arsenal breaking the chyme up for final absorption in the Jejenum.

These include;

  • Lactase, sucrase, maltase & alpha dextrinase for carbohydrate
  • Aminopeptidase & dipeptidase for protein
  • nucleoside & phosphatase for nucleosides (DNA)


The vast majority of nutrient absorption, from the gastrointestinal tract into the blood stream, takes place in the Jejenum.

The Jejenum is comprised of cells called enterocytes that line the intestinal wall, containing a structure of circular folds called villi and microvilli (see image below). This physical structure increases the surface area of the small intestine, so allowing for superior absorption of all essential nutrients. The lining of the intestinal wall at this point is only one cell thick, which further facilitates enhanced nutrient absorption.

Indeed, whilst the average size of the whole digestive tract is estimated to be at least 30-40 square metres, more than half of this is attributed to the Small Intestine alone.

Each different macro (fats, carbohydrates & protein) and micro nutrient (vitamins & minerals) group has differing methods of transport from the Jejenum, through the enterocytes, and out into the bloodstream for distribution and use by all cells of our body.

In our previous posts, we have already shown how dysfunctions in one aspect of the digestive process, may have detrimental consequences to other areas of the Gastrointestinal tract (e.g. anti-bacterial properties of optimal stomach acid on H Pylori).

So we hope that the message of everything having a pronounced “butterfly effect” or that “nothing happens in isolation” is now becoming clearer.

Rather than describing all the various methods by which each nutrient is absorbed, it is more important to understand why these nutrients may NOT be properly absorbed, how this may originate, what conditions and effects this may cause, and how to help prevent this.

Which leads us onto our next area of discussion (over several future posts), concerning how the composition of our diet, lifestyle & environment, primarily alters our digestive health & performance which leads onto many of today’s seemingly unrelated, but now all too familiar, chronic diseases.

Next Post: Intestinal Permeability

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