Leaky Gut Syndome Part 1: Understanding the Gut

They say you don't appreciate what you have until it's gone. Similarly, I think you don't truly appreciate good digestion until it's gone. For a shrinking part of the population digestion simply doesn't cross their minds, but with the increased incidence of Celiac disease, Crohn's disease and Ulcerative Colitis (both considered types of Inflammatory Bowel Disease, or IBD), gastroparesis, and Irritable Bowel Syndrome, digestions is on more people's minds than ever now.

So what do all these gut problems share in common? Even though each of these have their own set of diagnostic criteria and symptoms, what if they were all in fact part of a much longer problem?

Leaky gut syndrome, also known in the scientific literature as "impaired/increased intestinal permeability", is exactly what it sounds like. The gut barrier can become compromised for a number of reasons, and when it does it is less able to control what comes in and out of the gut. We will get into the gravity of this situation a little later, but first I want to explain normal gut function and how important it is.

Before you can understand abnormal you must understand normal. The gastrointestinal tract (GIT for short) is actually considered to be outside the body. Remember those weird water tube toys from the 90's? They were one continuous loop of plastic with one hole at either end and water inside.When you tried to hold onto it, it would turn in on itself making it nearly impossible to grasp (not unlike a slippery bar of soap). The human body is really no different: we are a tube within a tube. This makes the gut lining's job even more important- not only is each epithelial cell in charge of absorbing good nutrients from our food, but they have to be able to keep the unwanted crud out. This includes allergens, unfriendly critters, undigested food particles, chemicals, and potential toxins.

There are two ways that stuff can get into our bodies through the gut lining- by going between the cells or through a cell. These are called the paracellular pathway and the transcellular pathway. Each cell is held together by "tight junction proteins" called occludin and zonulin. When these proteins are destroyed or weakened the paracellular pathway becomes compromised, allowing passage into the underlying tissue. Transcellular passage happens when cells are destroyed (an example of this that you can actually see on biopsy is the villous atrophy seen in celiac disease) or when they fail to do their job properly.

The gut is home to approximately 70% of your immune cells- a brilliant tactic by the body if you ask me. With all the stuff our gastrointestinal system comes in contact with (food particles, chemicals, critters) it makes sense to put the guards of our bodies there to wait for the ambush. The analogy I like to use is if you were going to build a castle, where would you put your guards? Would you have them in a room inside the castle, or would you have them poised to defend you at the gate should the moat fail to stop your enemies?

Under normal conditions your gut has several lines of defense to protect itself. The first, and one that people often forget, is your digestive enzymes. Few bugs can actually survive the harsh, acidic environment of the stomach, so stomach acid serves as a great disinfectant right off the get-go. Not only that, but the digestion of food by our acids and enzymes breaks down the large molecules such as gluten and casein so they can be more easily metabolized by the enterocytes. Without proper digestion by these enzymes, large otherwise harmless macromolecules such as gluten are allowed to come in contact with new areas of the GIT as well as the immune system.

In the intestines (where the vast majority of our food is actually absorbed) there are several other defense mechanisms in place. The immunoglobulin IgA is abundant in the gut and aids in the binding and removal of antigens and bugs. Additionally, the microbes that make their homes in our guts play an immensely important role in our health. These microbes help modulate the immune system and relay information to the underlying dendritic cells and enterocytes. Some bacteria actually make things for us that we would otherwise not be able to make ourselves, like vitamin K. These critters are in constant communication with our cells as well as each other, and we are just starting to understand just how important they are.

Up next: What causes leaky gut syndrome?

Nikki

Resources:
A great TED video about bacteria:
http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html

Pictures taken from: 

Menard S, Multiple facets of intestinal permeability and epithelial handling of dietary antigens, 2010 May, Vol 3 Issue 3, P 247-259.