It’s a Journey – The Digestive System

We started this journey on the highway, 60,000 miles of blood stream delivering everything to and from everywhere. You learned (at a very high level) how the highway is structured, how it can be damaged, and the consequences of damage.

Two systems provide the primary everything to the blood stream, the lungs (oxygen) and the digestive system (nutrients). The initial entrance for both is the mouth and nose but the path divides into two at the back of the throat.

In this post you saw how lungs can be damaged and why that isn’t a good idea. Moving right along, it is time to look at the digestive system. This is where things can get really complicated.

Odd as it may sound, complications start with the immune system. Seventy to 80% of your whole immune system resides in your intestines. Why? Because most of the the stuff that will makes you sick and activate your immune system will arrive through your digestive tract.

For that reason I chose last week to repeat an earlier article describing the immune system as a preface to the digestive system itself. With that preface now we can really move along.

The Goal of the Digestive System

Nutrients that your clever body can’t produce itself come from food and the digestive system’s goal in life is to break down food into simple molecules that can be absorbed into the blood stream. That breakdown starts in the mouth, passes into the stomach, and finishes in the small intestines. Left over, known as waste, moves into the large intestines and then out through the rectum.

If you yearn for more detail try this simple link, .

In order for all that digestion to work properly, gastric juices (like stomach acid and bile) and enzymes are required to do the breakdown. Hormones, on the other hand, are in the chemical instruction business telling enzymes and pretty much everything else what to do.

Technically the pancreas, liver, and gallbladder are heavily involved in the digestive process.

Working properly presumes three things:

  • That your genes (DNA) allow for the right levels of those enzymes and hormones. Not too much or too little. In science this is called “homeostasis.”
  • That food includes the required vitamins/minerals and water.
  • That foods creating allergic reactions and triggering autoimmune responses are avoided.

Here there is an infinite possibility for stuff to go wrong.

Let’s assume, just for the sake of conversation, that the structure of all your body parts including your stomach and intestines arrived at birth in reasonably good working order. So how does the digestive process go awry?

The intestines contain trillions (literally) of bacteria called microbiota that are active participants in digestion. Some of those bacteria are good, some are not – it’s an ongong battle with balance as the goal. When out of balance, bacterial overgrowth can make a mess in the small intestine.

The Lining of the Intestines

The lining of the intestines has tight junctions, forming a barrier that is supposed to allow digested nutrients and water into the blood and keep undesirable stuff from getting out of the intestines. The structure of the barrier is complex and requires a number of vitamins and minerals to function correctly..

Undesirable stuff is incompletely digested food, the microbiota themselves (which aren’t supposed to leave), allergens (anything that causes an allergic reaction), pathogenic (bad) bacteria arriving in food, viruses, toxins, parasites etc.

The Immune System

The immune system is part of the barrier, It has a big job dealing with all the undesirable stuff. Note that in these cases the immune system is attacking something that isn’t supposed to be there — that really is its job.

Sometimes, however, the immune system can go awry, attacking something that IS supposed to be there. This is an autoimmune disease. For example in Celiac disease the immune system actually attacks the intestine itself. Gluten triggers the autoimmune reaction in Celiac.

Just like when you cut your finger or break your leg, the first action of an engaged immune system is inflammation. Acute inflammation is expected and desirable, otherwise why would there be an immune system at all!

Chronic inflammation, however, is different. The more ongoing inflammation the greater the likelihood that the intestinal lining will be damaged, junctions will open, and undesirable stuff will escape. This is called a leaky gut.

Now we have stuff in the blood stream that doesn’t belong and the immune system has a whole new job.


Pat Smith is the author of “It’s All about the Food,” a book that guides nutritious food choices as the way to avoid illness and maintain a healthy weight. Proceeds from her book benefit the Montgomery County Food Pantry. Her website is She can be contacted at, 501-605-3902. Her Facebook page is