The phases of nutrition – digestion and assimilation -Physiology and stages

Digestion and assimilation ? Has anyone ever heard that “we are what we eat”? Hardly! But this thought is both true and inaccurate, because we are rather what we digest, absorb and transport to our cells.

Do you know what happens to your food from the moment you put it in your mouth? Do you know how many hours it travels through the different structures of the digestive system and what happens in each phase?

Let’s understand to emphasize once again how important it is to take care of good digestion and optimal functioning of the digestive system, because it is no coincidence that the gastrointestinal tract is called the “second brain”.

From food to micro- and macronutrients

An optimally functioning digestive system can digest and assimilate about 97% of the food we eat, but this percentage can be drastically reduced in the presence of various intestinal diseases, food intolerances, the predominance of bad bacteria in the intestinal flora and others. The main function of the digestive tract is to extract important substances from food, to protect it from harmful microorganisms trying to enter the bloodstream and to dispose of waste products left at the end of the process.

From the mouth to the intestines or what is the structure of the digestive system

After chewing the food well and swallowing it, it goes on a few hours of adventure through the digestive system. Why a few hours? Because its length varies between 6 and 7 m – something impressive, especially against the background of human height. It starts from the mouth and ends with the anus.

We will look at the following parts of the structure in a little more detail:

  • oral cavity;
  • esophagus;
  • stomach;
  • small intestine and large intestine (and their individual parts).

Digestion in the mouth and esophagus

The mouth is the entrance to the digestive system, where food enters and is broken down into smaller particles by chewing. Additionally, with the help of saliva, these particles are coughed up. It is important to mention that in some cases a small part of the absorption of substances occurs in the mouth.

It undergoes mechanical and chemical processing of food. It is mechanical through the teeth, tongue and cheek muscles, and during this stage we have the food being broken down and torn, which is moistened by saliva and turned into a ‘bolus’.

Saliva is responsible for chemical processing because it contains various substances, including enzymes (eg amylase, maltase, lipase). The salivary glands in the mouth produce about 1.5 liters of saliva per day. Thus, the food bite is chewed and formed with the help of saliva, then passes through the pharynx and enters the esophagus to continue its way to the stomach.

The name of the esophagus (esophagus) comes from the ancient Greek language (“oiesin” – to carry and “phagein” – to eat) and indicates the function of this part of the digestive system, namely – to transport food from the mouth to the stomach.

The esophagus ends with a one-way valve called the lower esophageal sphincter or cardia, whose function is to allow food and fluids to enter the stomach from the esophagus, but to prevent them from returning to the esophagus. However, it happens that the sphincter does not close properly (or completely) or opens at the wrong time. Then there is gastroesophageal reflux, accompanied by burning, pain, nausea.

Digestion in the stomach

The stomach is where the main digestion of food begins. It is located between the esophagus and the small intestine. Here, through the release of stomach acid, the bites are broken down into smaller particles called porridge. Stomach acid has another important function – to destroy most pathogens that enter with food. The acidity is high – during digestion the pH value approaches 1.

A curious fact is that an empty stomach is very small, but depending on the food and fluids consumed, it can increase its volume up to 50 times and reach almost 4 liters capacity. After a portion of food enters the stomach, the gastric juice and the enzymes contained in it begin to act on it.

The stomach muscles mix the food so that as much of it as possible comes into contact with the gastric juice, thus reducing the time of digestion, while improving its effectiveness. The stomach is made up of 4 layers, each of which has its own specifics, but together they are responsible for transporting food to the intestines through the stomach muscles.

The next step of the food, already turned into porridge, is to enter in portions in the duodenum, which is controlled by a muscular opening. This entry is slow, and the porridge includes partially digested food, water, acids, and digestive enzymes. The time to empty the stomach varies between 1 and 4 hours, depending on the amount and composition of food.

Absorption in the stomach

The absorption of substances in the stomach is minimal, but small amounts of various mineral salts, water, alcohol, as well as most drugs are absorbed through its cell walls. Therefore, the stomach can be defined as a digestive rather than an absorbing organ.

Small intestine – structure, digestion and assimilation

The small intestine consists of three main parts:

  • duodenum (the first part after the stomach);
  • empty intestine;
  • ileum.

The third part ends with an ileocecal valve that blocks the entrance to the colon. The path from the entrance to the small intestine to the ileocecal valve is very long – the slurry progresses by about 1 cm per minute, and the entire distance travels for a period between 4 and 8 hours.

After entering the duodenum, the food porridge (chyme) is subjected to the action of enzymes contained in juices secreted by the bile and pancreas. Juices, in turn, consist of bicarbonate, lipase, amylase and proteolytic enzymes.

The small intestine has a strongly folded inner surface covered with hairy cells, which makes it an excellent absorption organ, thanks to its large suction area.

At the beginning of the small intestine is the absorption of simple sugars and fat-soluble vitamins, down is digested undigested disaccharides, amino acids, fatty acids, glycerol, after which water-soluble vitamins and bile salts are absorbed.

Thus, as the slurry moves through the small intestine, proteins, fats and carbohydrates are finally digested and most nutrients are absorbed. The next phase of the food porridge is to enter the colon.

Colon

Like the small intestine, the large intestine also consists of three main parts:

  • appendix (caecum);
  • colon;
  • right intestine (rectum).

The content that reaches the colon is from indigestible ingredients in the chyme, water, and some of the digestive juices. The main compounds entering the bloodstream through the walls of the colon are water and the ions dissolved in it. Waste material (feces or feces) remains, which is excreted from the body. This usually takes between 12-25 hours (from the entry of the food slurry into the colon, to the disposal of the waste product).

These are the main functions of the colon – one is to suck water and the other – to excrete feces. As you can guess, the colon contains the most numerous and different types of bacteria in the digestive tract.

We can distinguish two types:

  • Degrading carbohydrates that our body has failed to digest and assimilate (eg fiber, oligosaccharides and sugars). During the fermentation process, short-chain fatty acids are formed, which have positive properties;
  • Degrading proteins such as enzymes, dead cells, collagen and elastin from our food.

It is important to maintain a healthy balance of bacteria in the gut in order to:

  • prevent harmful bacteria from taking over,
  • remove carcinogens,
  • strengthens the immune system,
  • prevents allergies and various intestinal diseases.

Let’s summarize

The digestive system extracts the main nutrients from food and beverages once they enter it, absorbs the necessary macro- and micronutrients, and serves as a barrier against potentially harmful microorganisms. The digestive tract begins at the mouth and ends at the anus.

This time is passed from the food / food porridge for a period between 18-72 hours. The duration depends on the individual’s eating and exercise habits and is reduced if a diet rich in fiber and fluids (fruits, vegetables, nuts, seeds, whole grains, legumes, etc.) is consumed, as well as if regular physical activity is present in a person’s daily life. activity.

The digestive system is a long muscular canal where various fluids (stomach acids and alkaline fluids in the intestines) and enzymes are secreted, and in combination with rhythmic contractions, our food breaks down into smaller pieces and moves along the chain until complex molecules break down into simpler ones. A healthy digestive tract is necessary for optimal digestion, absorption of substances and their delivery to the cells that need them.

A properly functioning gastrointestinal tract is extremely important for a person’s overall health and well-being because it covers 75% of the body’s immune system, but unfortunately most people often wait to feel unwell to take care of their “second brain”.

Digestion and assimilation

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