The Human Digestive Tract

What the human digestive tract looks like

The human digestive tract is a 30-foot-long tube, with lots of folds and bends, of varying surfaces and purposes, that runs from the mouth to the anus.  Centered around the small intestine, extending upward to the stomach, downward to the large intestine, and sideways to the supporting organs, the “gut” as we call this area is the foundation of human health or disease.

Focusing in on where the action’s happening, we find a semi-permeable section of the gut called the small intestine that serves as our primary border between us and the outside world.  The cells lining this section of the gut wall heavily influence what happens in all other areas and functions of the body. It’s the membrane through which nutrition, hydration, toxins, and pathogens either passes, or gets blocked.

Equally important, a border is nothing without personnel to tend it and protect it.  So this area is filled with a wide variety of microscopic life forms that we now collectively call the microbiome.  This microbial community actively detains and deports harmful substances.  It maintains the physical integrity of the intestinal wall by nourishing its cells.  And it helps feed the entire body through digestion and absorption.

Things you eat don’t become part of you until they pass through the gut wall and enter the bloodstream

Curiously enough, as food travels through the digestive tract, for all intents and purposes, it’s still part of the outside world, and not part of you.  Meaning, food products have to get through the intestinal wall and reach the bloodstream to become part of you and give you nutritional benefit.  Until that happens, food products in the gut are considered transient.  They’re isolated from you, and can go right through you.  The result is next to no nutritional benefit.

For that reason, the intestinal wall has a complex surface with lots of folds, or finger-like protrusions. These are called villi and they optimize surface area and absorption capability to epic proportions.  If you were to lay all the folds of the intestine flat, it would cover a tennis court.

This enormous surface area increases the intestine’s ability to pass food.  Then it gets been broken down through its walls and into the bloodstream, where it then becomes part of you – perhaps only for a while.

But here’s the danger.  This massive surface area–your cells, internal organs, and you on the other side of that barrier, leaves a lot of real estate vulnerable to “unauthorized access.”  In other words, when the gut lining is porous and leaky, this huge surface area becomes a liability.   This allows intruding organisms and substances to get through.

The gut wall is basically a border like no other that needs a defensive shield.  So Nature covered every square millimeter of our gut wall with a thick layer of bacteria and other microbial life – called our “gut flora” – or “microbiota” as it’s now called.

This gut flora forms a barrier that’s crucial to our nourishment and protection.  It’s comprised of (in a perfect microbiome) many hundreds to thousands of different strains of bacteria, yeasts, viruses, fungi, parasites, and even mold – totaling around 3-5 pounds and several trillion individual cells.

But, as we’re all learning, one way or another, a healthy gut is becoming the exception, not the rule.

The finger-like protrusions that line the gut are called villi (plural).  And every “villus” (singular) is covered by a layer of “enterocytes” one-cell thick along its surface, like having wall-to-wall carpeting.

Enterocytes are the cells that complete the digestive process by breaking down food particles and then absorbing them.  They also serve as a “castle wall” by blocking harmful substances from getting into the body (when it’s healthy and intact).

Enterocytes work so hard at digesting and defending

Enterocytes are born at the bottom of “the crypts,” which is basically the valley between villi.  Over the course of 3-5 days, enterocytes move up the villi like riding an escalator, as they perform functions of digestion and absorption.  In 3-5 days’ time, they mature, die, and are shed off.

Critical to proper digestion, each enterocyte has long hairs on its head called “microvilli” that perform the last steps of digestion.  These microvilli produce enzymes that break down food particles into molecules the body can use.  And these microvilli form a so-called “brush border” along the surface of the small intestine that radically increases the digestive capabilities of the villi and GI tract due to its incredible surface area.

One of the hallmarks of Gut And Psychology Syndrome is ailing enterocytes.  Enterocytes weaken when they are mal-nourished and exposed to toxins and pathogens.  Their journey time up the villi can double.  So you have old, decrepit enterocytes trying in vain to do the work of fresh, young enterocytes.

Along with that, the hair on their heads get fried, which prevents the microvilli’s enzymes from completing last stage of digestion.  As a result, food particles are never fully broken down into molecules the body can use.  So now they enter the bloodstream in a harmful form.  Partially-digested proteins are notorious for causing the most damage.

Zooming back out, each enterocyte is firmly, but release-ably, joined to its neighbor by an adhesive-like protein called a “tight junction.”  This is similar to the hook and eye design of Velcro.  Essential to controlling the movement of things through the gut wall, a protein called “zonulin” regulates the permeability of these tight junctions.

Under normal circumstances, the amount of zonulin produced by enterocytes tightly controls the extent and timing of the “zippering” effect that lets things through the gut wall, because zonulin is the chemical messenger that tells the enterocytes when to open (by its presence) and when to shut (by its absence).

Like opening and closing Velcro, zonulin orchestrates the passage of nutrients and other stuff through the gut into bloodstream, as well as immune cells out of the bloodstream into the gut.