Digestive system

This subpage on the digestive system constitutes the second part of the theory for Biotech Academy’s material on the Body and Diet.

 

The food we eat is about to travel 12-36 hours before it has made its way through the body.

In order for the cells to absorb the nutrients, the food must first go through the entire digestive tract, which consists of: Oral cavity, esophagus, stomach, duodenum and small intestine, colon and rectum. Along the way, many different enzymes help break down food. Figure 4 shows how the digestive tract is structured, as well as the digestion of the individual nutrients.

 

Mouth and stomach:

The food is first finely divided into the mouth, kneaded and mixed with saliva. The saliva contains some enzymes that cleave the carbohydrates. In the stomach, the kneading of the food, which is mixed with gastric juice, continues. The gastric juice consists, among other things, of an enzyme that cleaves proteins into amino acids. On average, it takes about 3-4 hours to empty the stomach. However, this does not happen all at once, as only small portions are let out into the duodenum at a time.

 

Intestine and liver:

When the food arrives at the duodenum, it is in liquid form. In the duodenum, it is mixed with pancreas, bile and intestinal juice. The pancreas and intestinal juice contain enzymes that cleft:

  • Protein to amino acids
  • Fats for glycerol and fatty acids
  • Carbohydrate for monosaccharides

The liver produces bile, which is sent to the gallbladder, from where it is excreted. Among other things, bile ensures that the fat is finely divided into small fat droplets. It is already in the duodenum that some of the nutrients are absorbed (absorbed) into the blood or lymph. The intestinal contents are then passed on to the small intestine by means of muscle contractions. The breakdown of nutrients continues here, where they are also absorbed into the bloodstream or lymph and thereby sent on to the cells. In the cells, nutrients are converted into energy. And without energy, the cells would not survive.

However, not everything is absorbed. The rest is pushed on to the colon, where the water in the intestinal contents is absorbed, so that the intestinal contents become more firm. The longer the intestinal contents are in the colon, the firmer it becomes, and in the worst case, it can cause constipation.

The last part of the digestive tract is the rectum. Here, the intestinal contents slide down, and when the rectum is full, a message is sent to the brain, which creates an urge to go to the toilet.

The digestion of each nutrient is described in detail here: digestion of proteins, digestion of carbohydrates, digestion of fats.

Figure 4. The task of the digestive system is to digest and absorb (absorb) the nutrients in food. In the figure, each organ is marked with a color. The different steps during the digestion of each nutrient are marked with a color and refer to the organ on the figure. The food’s nutrient content is broken down in different ways. Carbohydrates must be broken down into monosaccharides and then absorbed directly into the bloodstream. Proteins are also broken down into smaller molecules called amino acids, after which they can be absorbed into the bloodstream. The breakdown and absorption of fats (triglycerides) is more complicated because they are not miscible with water. They are first broken down into glycerol molecules and three fatty acids, after which they are restored to triglycerides in so-called kylomicrons. Triglycerides are first transported into the lymph via kylomicrons, after which they are released into the bloodstream.

Did you know that the small intestine is about 4 meters long and its surface is about 200 m2. It corresponds to the area of a small football field. The large area is due to the fact that the inside of the small intestine is covered with small so-called microvillia, which provide a very large surface.