Gastric juice is a very active fluid that consists of hydrochloric acid and various enzymes (which break down nutrients). Hydrochloric acid also has a detrimental effect on microorganisms that enter the stomach through the mouth. During the day gastric juice produces approximately 1.5 liters. In order for such a potent fluid as gastric juice, not to damage its own wall of the stomach, on its surface there is a special “pad” of mucus, which, like a bulletproof vest, protects the stomach from self-digestion.
The gastric mucosa, on the one hand, is affected by the components of the gastric juice – hydrochloric acid and enzymes that break down the protein, on the other hand, their aggressive action is opposed by the system of protection of the stomach, which is developed by itself against its own factors of aggression. Aggression factors include gastric juice and the food we take. Food can also sometimes damage the stomach lining (for example, if it is very hot or badly chewed). Too hot or spicy food can also damage the delicate inner lining of the stomach, because solid food remains in the stomach for about three hours. So the poor stomach has to defend itself from the burning effects of pepper, vinegar or mustard for three hours. And how long will his reserves last.
The factors protecting the stomach from aggression factors include the ability of the stomach to produce mucus and bicarbonate, that is, ordinary soda, which neutralizes the action of hydrochloric acid, and the ability of the cells of the gastric mucosa to be updated very quickly (every 2-6 days). Damaged cells are destroyed. An important support to this protection is provided by intensive blood circulation in the walls of the stomach, because the blood supplies nutrients and oxygen to them – in these conditions, cells can grow quickly and often be updated.
The stomach will work properly only if there is a truce and balance between the factors of aggression and defense.
Directly in the stomach itself, nothing is absorbed, except water and alcohol. Protein and carbohydrate food leaves the stomach in about 2–3 hours, but fats remain in it much longer – about 7 hours.
Hydrochloric acid is very important for digestion in the stomach, since enzymes that break down nutrients can only work in an acidic environment. Even the academician Pavlov has proved with his experiments that gastric juice, like saliva, is released when looking at ready-made dishes, especially if they look appetizing. Even if you just think about food, gastric juice will immediately begin to stand out. Not only food affects the secretion of gastric juice, emotions can also change its production.
From the stomach, processed food enters the small intestine, the length of which in humans is approximately 5–7 meters. In the intestine under the action of intestinal juice (in the formation of which the liver and pancreas are involved) proteins, fats, carbohydrates break down into easily digestible components, which are absorbed into the intestinal walls and enter the bloodstream.
The inner surface of the walls of the small intestine has many outgrowths and villi and resembles velvet. These villi allow many times to increase the suction surface of the intestine (in general, it is 400 square meters – the size of the basketball court).
In the small intestine food is 5-6 hours, and then enters the colon. The function of the colon is the mixing of digested food, the absorption of water and salts, and the decomposition of fiber with the help of bacteria. Bacteria of the colon are also capable of producing a number of vitamins needed by man. Ending the process of digestion, as is known, the formation of fecal masses and their excretion.