Know Your Complete Gastrointestinal Tract To Stay Healthy


A simple explanation of our complete gastrointestinal tract

Roughly speaking, there is a distance of twelve meters and 70 hours between food intake (eating and drinking) and excretion (you know …). What happens in between in the gastrointestinal tract is quickly overlooked. Too bad – because our digestive tract is hard to beat in superlatives and interesting tasks!

Read more about digestion here in detail and what common problems can arise. You will also learn what influence the gastrointestinal tract has on the development of autoimmune diseases.

Facts about the gastrointestinal tract

I think this immediately shows how interesting our digestive system is:

1- The stomach is almost as acidic (pH value) as a car battery (see gastritis)

2- In the course of life, our gastrointestinal tract has to digest around 45 tons of food, which corresponds to nine adult elephants

3- The small intestine is eight to ten meters long, the large intestine about two meters

4- The entire intestinal tract (small intestine and large intestine) has a surface area of ​​180 m² (half a football field) but is only a few thousandths of a millimeter thick

5- A drop of colon fluid contains more living things than there are people on earth

6- Most of your immune cells are in the intestine – it gets hot there!

7- You have several 10,000 nerve cells directly in the intestine – there is something to the so-called gut feeling

Now, do you understand why we are so fascinated by our digestive system here? And not only since Giulia Ender’s book *”Gut: The Inside Story of Our Body’s Most Underrated Organ”.

Your health is basically decided here – in the gastrointestinal tract. Sick or healthy, well-fed or lack of nutrients – all of this is decided in the gut!

Our small gastrointestinal tract

Imagine you are an apple. A human eats you, and you travel through the entire digestive system. How does that work?

You’d get mechanically crushed in the mouth, mixed with saliva and swallowed. The apple porridge migrates through the esophagus into the stomach, where it gets acidified.

This kills bacteria on the surface and swells proteins and fiber so that it becomes “more digestible”.

Through the gastric portal, it goes over the duodenum towards the small intestine. In the duodenum, digestive juices from the pancreas and bile mix with the apple porridge.

These contain enzymes that break down the proteins and carbohydrates, as well as bile salts that absorb the fats.

Common Gastrointestinal Problems And Their Impact On Health 

The small intestines get the lion share of nutrients

Because they don’t contain fat, bile is important for fiber. Bile salts consist of cholesterol and fiber draws them into the intestine. By the way, the body also gets rid of excess cholesterol.

The small intestines absorb the most important nutrients, which are eight to ten meters long: Sugar, amino acids (breakdown products from protein), fat, vitamins and a large part of the water.

After a few hours, the process continues in the large intestine, where the last remaining water gets absorbed and the intestinal bacteria ferment the fiber.

Once the fiber has been broken down and the bacteria have had their feast, everything that remains (and a few bacteria) will be excreted. And that ends up in the potty.

So it takes up to three days for an apple to be fully digested. The longest time period takes place in the large intestine, i.e. the fermentation through bacteria. They are rather cozy and take their time at work.

The following is a detailed look at the individual parts of the digestive system:

Gastrointestinal tract structure and functions


The stomach is, and that sounds insanely unfriendly, but it is the truth, a lump of meat covered with mucus. This is important if you know what the stomach has to do:

It is the most acidic part of the whole body. After the mechanical crushing in the mouth, the acid in the stomach has to chemically crush the food. Proteins and fiber, in particular, are inherently dense and difficult to digest.

Gastric acid is essential so that these components unfold like a rolled-up newspaper: Before you want to read every single page, you have to unroll and unfold the newspaper. It happens in the stomach.

Another important function is the disinfection of food. Everything we eat, unless it is produced and cooked sterile, contains microorganisms.

Bacteria, viruses, molds, fly eggs – all kinds of creatures. The stomach acid kills these creatures so that they cannot end up in the intestine and infect the body.

As you can see, stomach acid is absolutely essential for the work of the stomach. It becomes more problematic if it becomes too acidic, or if it is not acidic enough.

Then the risk of gastritis (inflammation of the stomach) or irritable stomach increases as well as the well-known heartburn.

At the same time, the cells in the stomach have to protect themselves from the acid. That is why they are surrounded by a thick layer of mucus. The acid cannot harm the cells.

Other tasks of the stomach are the production of digestive proteins (pepsinogens, intrinsic factor). But these will not be so important today.

In summary, the main tasks of the stomach are disinfection of food, crushing, acidification and destruction of food components.

The mixing of the food pulp and maintenance of the mucus layer to protect the stomach cells is also vital.

If the food gets acidified and mixed enough, the gatekeeper lets this acidic porridge go towards the small intestine.

Small intestine

In the duodenum, the food pulp is deacidified from the stomach and mixed with digestive juices. These digestive juices are important for later nutrient intake.

You will notice that the intestine can only absorb certain substances from food. If he were to absorb everything that was floating around, toxins and disease carriers could get into the body unhindered. That would be fatal.

Therefore, added digestive juices make it easier to pick up more later, such as digestive enzymes that break down carbohydrates and proteins. These same juices also collect bile salts for fat absorption and bases for neutralizing stomach acid.

These are several liters of digestive juices every day added to the porridge. Quite a bit of drudgery that digestion has to deal with in the course of life.

The duodenum’s name origin

The duodenum is so named after the Greeks ” dodeka daktulon” meaning twelve fingers, which is its size when placed side by side.

The small intestine is by far the longest part of the gastrointestinal tract. It has such a large surface area that it can absorb as many nutrients as possible from the food.

Pure efficiency! It is sparsely populated with microorganisms. It is also a good thing so that the small unicellular organisms cannot snatch away important nutrients from the body.

The immune system, therefore, monitors very closely how many unicellular organisms are in the small intestine and intervenes when there are too many.

If there is an over-colonization with microorganisms (SIBO), this is a problem for the entire health.

The huge surface of the small intestine comes from a multidimensional protrusion of the intestinal cells. A large surface also means that the area is prone to injury.

If this happens, holes in the intestine (leaky gut syndrome) can occur. That is part of another article.

The intestinal layer is only a few thousandths of a millimeter thick, just as thick as a cell. Significant tasks await this one cell layer. They are exposed to the constant bombardment of toxins and individual pathogens.

An average intestinal cell survives only five days before it dies and gets replaced with a new cell. This is also an important trigger for leaky gut syndrome. The intestinal cells simply have too few nutrients to be able to grow back quickly enough.

When the food components break down, they enter the bloodstream through this cell layer and nourish your body.

All that is left of the food pulp is now only fiber and a little water. Carbohydrates, proteins, fat, salt and vitamins have mostly been ingested. The colon does the rest.


The well-known appendix lies between the small intestine and the large intestine. Well known because everyone knows someone who has had their appendix removed. Until recently, people had no idea what the appendix’ job was (some people still don’t know).

The appendix is ​​a kind of stub, a dud. The most common theory is that the appendix is ​​a reservoir for intestinal bacteria.

If the intestinal flora in the large intestine is completely erased as a result of a bad infection or another disease, there are still enough bacteria in the appendix to colonize the large intestine again.

This is important so that no harmful bacteria and molds colonize the empty colon.

Accordingly, the appendix is ​​not essential for survival. However, it was beneficial in human evolution when an acute intestinal infection occurred. The appendix has no effect on the actual digestion.

Note: Inflammation of the appendix was also a death sentence up to 200 years ago – today a small operation is enough. But an intestinal infection is much more common than an appendix infection.

Large intestine

This part of the gastrointestinal tract is one to two meters long, but almost as thick as a fist. In direct comparison, there are a million times more bacteria than in the small intestine.

First, water gets absorbed from the food porridge in the large intestine, just like salts.

So the feces are being prepared. Since water is vital, all possible fluid gets removed from the food pulp.

At the same time there are the intestinal bacteria or rather the intestinal flora. The intestinal flora metabolizes everything that is left in the porridge and can be used.

You carry about 4.4 pounds of bacteria in your colon every day.. But don’t come up with the idea of ​​wanting to “trim down” these few pounds. Because these little helpers in the intestine are vital! Their tasks are as follows:

1- Breakdown of fiber into short-chain fatty acids that the body can absorb.

2- Production of vitamins and hormones for the body

3- Constant communication with the immune system, hence “training” of the immune system.

4- A procurator in the colon so that no pathogens can settle there

5- Direct communication with the brain (gut-brain axis) and, thus, influence your happiness and well-being

That is why it is so important to take care of the intestines. Not only the small intestine so that it can diligently absorb nutrients, but also the little helpers in the large intestine. They are not the enemy, they are vital!

The goal should be to keep the intestine active and without damage and to maintain the right intestinal bacteria. You can find out how in the article on foods for a healthy intestine.


We have not been talking about porridge for a long time, but about stool. Ideally, it is firm, but not too firm. Too tight would mean that the intestinal wall would be damaged if the porridge made its way there.

The stool consists of approximately 50% indigestible fiber and its waste products and 50% bacteria – dead and alive. There is a constant coming and going in the gut, even with the little helpers. The rectum temporarily stores and checks the feces:

How firm is the stool, how much is it, what is the composition? Is it acid, or gas it gas included? Diligent intestinal cells check this and tell the brain when it’s time to go on to the potty:


You know what is happening here. 😉

*Giulia Enders - Gut: The Inside Story of Our Body's Most Underrated Organ

Dear co-creators

Now you know how the digestion works and what happens in detail within our gastrointestinal tract. But you’re surely here too, because you want to know what problems can arise in the intestine, right?

In my following article, you will discover what happens when something goes wrong in the intestine and what health problems can arise in everyday life.

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