Digestion – A food journey through the body

The food pulp mixed with saliva has now arrived in our stomach. The food is first stored in the upper part of our stomach (fundus) before soon being processed further in the lower sections (corpus, antrum ).
The stomach can be described as a kind of muscular tube that sits in the left-hand side of the abdomen below the diaphragm. It produces 2 - 3 litres of gastric juices every day. Gastric juice contains, among other things, gastric acid, or more accurately hydrochloric acid, which makes the stomach a highly acidic environment. The food pulp is mixed with gastric juice by means of wave-like contractions of the muscles, and known as "chyme". In this acidic environment the salivary amylase first loses its effect, thereby ending the process of carbohydrate digestion. Now, the digestion of the protein components in the food can begin. The pepsinogen that is needed for this, an inactive precursor of the enzyme pepsin, is also contained in the gastric juice and is converted into the protein-degrading enzyme pepsin in this acidic environment.  Proteins are first reduced in size to large fragments in the stomach before being further processed and absorbed  in the small intestine.
By the way: have you ever wondered how your stomach is able to withstand the effects of the hydrochloric acid and the pepsin? Here the body finds its own solution, with specific cells on the surface of the mucous membranes producing an alkaline secretion that creates a protective layer over the surface of the wall of the stomach, thereby enabling the stomach to protect itself from the acidic environment. The wall of the stomach is protected against the enzyme pepsin since it is not activated until it has travelled further into the stomach.

Gastric juice has further important functions. Water-soluble vitamin B12, for example, which is contained in meat and dairy products, can only be absorbed later on in the intestine and then transported into the blood under the influence of gastric acid, and by being bound to a transport factor, "intrinsic factor", which is also contained in the gastric juice .

The residence time of the chyme in your stomach depends on various factors. If you eat a high-fibre diet, for example, the transport is delayed as the fibre attracts water and the resulting larger food fragments can only be transported slowly through the pylorus at the exit from the stomach. This has the benefit of helping you to feel full for longer. Foods with a higher fat content also delay gastric emptying. In addition to this, the residence time is affected by other factors such as stress, tension and emotional influences. Food can remain in our stomachs for anything between one and around eight hours .

Once our food has passed through our mouth, oesophagus and stomach, it then moves on to our intestines. The powerful contraction and brief opening of the pylorus ensures that the content of the stomach are passed on, portion by portion, to the small intestine. This process is controlled by the expansion of the walls of the stomach and the intestine (which in turn influences the degree of fullness), nerve impulses and various hormones.
To find out what happens in your intestines, read the article entitled “Digestion – A food journey through the body (stage 3:  the intestines)“.