Our digestion — an overview
We love to eat — but what happens to everything we swallow? How does our body draw energy from everything we eat? Our digestive system is highly complex and includes all the organs that serve to absorb our food, break it down, pass it on and convert it into usable nutrients. The organs of our digestive system basically have two main functions: transporting and processing all the food we eat by releasing hormone- and enzyme-rich secretions into these transport organs. All the digestive glands together — the salivary glands, gastric glands, intestinal glands, pancreatic glands and liver — help break down food and collectively produce about 8 liters of digestive secretions per day, 1.5 liters of which is saliva. Isn’t that crazy?
Little time, but you don’t want to miss anything? — All the facts at a glance!
- The organs of our digestive system basically have two main functions: the transport and preparation of all the food we eat
- All digestive glands together produce about 8 liters of digestive secretions per day — 1.5 liters of which is saliva
- Our digestive system is a 9 meter long tube
- Bread tastes sweeter the longer you chew it
- Carbohydrates leave the stomach fastest
- Fats are the slowest to be predigested, hence the saying “fatty food is heavy on my stomach”.
- With the help of various digestive enzymes, all components are broken down into small enough pieces so that they can be absorbed by the intestinal mucosa.
- The entire digestive tract has its own, largely autonomous nervous system in the wall
- With approximately 100 million neurons, the “brain of the intestine” has as many nerve cells as the spinal cord
- A single gram of intestinal contents harbors more living organisms than the earth harbors humans — mostly bacteria, but also viruses and fungi
- Our digestive system is strongly influenced by organs that at first glance do not have much to do with digestion (thyroid gland)
Where does our food go?
Roughly speaking, the digestive system can be seen as a 9-meter-long tube stretching from the head to the buttocks. Food is taken in through the mouth, where it is mechanically broken down by the teeth and, to some extent, the tongue. In addition, saliva is added to the food in the mouth, which, on the one hand, facilitates the swallowing process and, on the other hand, adds a special enzyme (amylase) to break down carbohydrates (starch). This breaks down complex carbohydrates into smaller, sweet-tasting sugar components. This is why bread tastes sweeter the longer you chew it. Saliva also contains antibodies for immune defense.
The food pulp passes from the mouth via the pharynx into the muscular esophagus and, through peristaltic (forward) movements, on to the stomach, where processing of the food components begins. In the stomach, however, digestion in the true sense does not yet take place, but rather a mechanical preparation. All food components are mixed together and broken down by the stomach movements — the acidic stomach acid kills most microbes and denatures proteins so that they can be more easily utilized by enzymes. Many enzymes work pH-dependently, so that certain food components can only be digested in certain environments.
Carbohydrates leave the stomach most quickly because they cannot be broken down further by amylase in the acidic environment of the stomach. As soon as the carbohydrates leave the acidic gastric environment and reach the less acidic intestinal environment, the enzymes again begin to break down the carbohydrates into their smallest components. Protein-rich foods, such as meat, remain in the stomach longer because they are broken down by the stomach’s own enzyme, pepsin. Fats are predigested the slowest, hence the saying “fatty food is heavy on my stomach”. Within a few hours, the stomach has transformed its contents into a soft food pulp that can be emptied further into the small intestine, where the actual digestion and absorption of nutrients takes place.
With the help of a wide variety of digestive enzymes, all the components are broken down into small enough pieces to be absorbed by the intestinal mucosa. Proteases break down proteins, amylases and dissachharidases break down carbohydrates, and lipases break down fats. The final stage is the large intestine, where the food pulp is thickened by dehydration, and indigestible food components (dietary fiber) are temporarily stored and excreted in a controlled manner.
Who controls digestion?
The entire digestive tract has its own, largely autonomous nervous system in the wall. The so-called enteric nervous system (ENS) is the “brain of the intestine” with about 100 million neurons extending from the esophagus to the anus. Thus, there are as many neurons in the intestine as in the spinal cord. The ENS coordinates intestinal movements, the secretion of digestive enzymes and juices, and the reabsorption of water and minerals. Many so-called transmitters play an important role in controlling intestinal movements. These include acetylcholine (increases digestive secretion production at rest), norepinephrine (decreases intestinal movements during stress), serotonin (increases intestinal movements). The brain controls and influences our intestines through the release of these neurotransmitters; stress and strain are also transmitted to the digestive tract in this way. Abdominal cramps, diarrhea or, in extreme cases, nausea and vomiting can be triggered in this way.
Not to forget the microbiome
Intestinal bacteria have long been known as digestive helpers, but in recent years have become an increasing focus and dominant topic in research. The balance or imbalance of this microbial ecosystem is thought to be responsible for autoimmune diseases, lipid metabolism or chronic inflammation. Billions of microorganisms colonize the inside of our intestines, and even produce enzymes that can break down food components that are actually unusable, such as dietary fiber, into components that the body can absorb and utilize. A single gram of intestinal contents harbors more living organisms than the earth harbors humans — mostly bacteria, but also viruses and fungi. An intact intestinal flora is also important both for the function of the intestinal barrier and for the containment of pathogens.
Hormones and digestion
What is often underestimated is that our digestive system is strongly influenced by organs that at first glance do not have much to do with digestion. The thyroid hormones, for example, but also most sex hormones have a non-negligible influence on our digestion. Since thyroid hormones cause an activation of the metabolism, hyperthyroidism (too much thyroid hormone) leads to an acceleration of all metabolic processes in the body, an increased basal metabolic rate, ravenous appetite, possibly weight loss, palpitations, inner restlessness or diarrhea.
In the case of a deficiency of thyroid hormones (hypothyroidism), on the other hand, metabolic activity is throttled back — resulting in weight gain, constipation, fatigue, hair loss, menstrual disorders and poor concentration. It is astonishing that besides diabetes mellitus (diabetes type 1, diabetes type 2), hypothyroidism is the most common hormonal disease in adults. Every tenth person is affected by hypothyroidism, women in a ratio of 4:1 significantly more often than men.
As you can see, the digestive system is too complex to cover in one article. Therefore, you can look forward to the upcoming series of articles about digestion!
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