Our gastrointestinal (GI) tract is considered to be outside the
body. In fact the the mucous membranes lining our GI tract
represent the largest surface area of the body exposed to the
external environment and all it contains, including
microorganisms and toxins. The job of the mucous membrane lining
the small intestine is to absorb fully digested nutrients - the
macronutrients (sugars, amino acids, fatty acids) and the
micronutrients (vitamins, minerals, and others) - while ensuring
undesirable microoganisms, toxins, allergens, and partially
digested foods are prevented from entering the body. In health
this is achieved by the cells that make up the mucous membranes
letting only small molecules pass through them and being tightly
packed together to form what are known as 'tight junctions'.
Properly functioning tight junctions prevent the contents of the
GI tract entering the body by passing through the gaps between
cells. Unfortunately various substances including alcohol,
medications (e.g. painkillers), foo