Digestion of food is an important process that directly affects the vital activity of our body. The very first food is processed in the mouth. But important will be her further path through the stomach. We will devote an article to this. We will analyze the phases of gastric secretion, consider the mechanisms of its regulation and other important topics.
Four groups of food by rate of digestion
The duration of assimilation of a particular food by our body is different. All food can be divided here into four categories:
- Carbohydrate food - digested fastest.
- Protein food - it takes an average time for assimilation.
- Fatty foods (plus its combination with protein) are products of a long assimilation time.
- A category of food that is not absorbed by the body, or is digested excessively long.
Digestion duration for each category
So how much food is digested in the stomach? Consider each category by time:
- 35-60 minutes. These are fruits, berries, liquid fermented milk products, juices (from fruits and vegetables).
- 1.5-2 hours. The category includes greens, vegetables, dairy products (excluding hard and oily), dried fruits, pre-soaked seeds and seedlings.
- 2-3 hours. Nuts, cereals, seeds, cereals, boiled legumes, mushrooms, bakery and hard dairy products.
- About 4 hours (or not digested at all). Categories include: meat, fish, coffee or tea with milk, canned food, most pasta.
Water that is drunk on an empty stomach does not linger in it, passing immediately into the intestines.
How much food is digested in the stomach and gastrointestinal tract?
On average, the time spent on general digestion of food looks like this:
- Staying food in the stomach - up to 4 hours.
- Digestion in the small intestine - 4-6 hours.
- The last stage (digestion in the large intestine) can take up to 15 hours.
Gastric secretion phases
So how is the process of processing eaten food going on here? The following phases of gastric secretion are distinguished:
- The brain phase.
- Gastric stage.
- Intestinal stage.
What do the stomach and duodenum do in their continuation, we will analyze in detail.
Brain stage
This phase is activated before the eaten food enters the stomach. It is aroused by smell, taste, type of food, or even thoughts of it. The more the appetite is increased, the more actively the body will produce gastric juice.
The nerve signals that occur in the cerebral cortex, appetite centers of the hypothalamus and amygdala are responsible for the brain phase. Further, these impulses are transmitted to the motor dorsal nuclei of the vagus nerve. From there (along the vagus nerves) they go directly to the stomach.
It should be noted that this phase of secretion will be responsible for approximately 20% of the total volume of gastric secretion, which is associated with eating.
The second name of the phase is complex reflex. It is connected with the fact that conditioned and unconditioned reflexes participate in it. It starts in 5-7 minutes, lasts at the same time 1.5-2 hours.
The scheme of the reflex arc here will be as follows:
- Receptors located in the oral cavity.
- Sensitive fibers of the brain, cranial centers.
- Vagus nuclei, medulla oblongata.
- Preganglionic nerve fibers.
- Ganglia.
- Nerve fibers postganglionic.
- Glands of the stomach, responsible for the secretion.
Gastric stage
What does the gastric phase consist of? As soon as food enters this organ, long reflexes from the stomach to the brain and back to the digestive tract, intestinal local reflexes, and the gastrin mechanism begin to be stimulated. Each of these elements causes the secretion of gastric juice within a few hours that the food is in the stomach.
The amount of secretion released during this phase will be 70% of the total mass. Therefore, the gastric phase is responsible for most of the juice produced. Its total volume per day is approximately 1500 ml. During the phase, hydrochloric acid in gastric juice kills harmful microorganisms contained in food.
The mechanisms at this stage will involve the following:
- Nerve central. Long reflex arcs stand out here. The path is as follows: gastric receptors - sensitive pathways - vagus nuclei (medulla oblongata) - preganglionic nerve fibers - ganglia - intramural - postganglionic nerve fibers - gastric glands responsible for secretion production.
- Nervous local. These include reflex short arcs that will close in the walls of the stomach itself.
- Endocrine. What stands out here? Gastrin, which is thrown into the blood endocrine cells of the gastric pyloric department. It stimulates the secretion (secretion) of hydrochloric acid by the glands of the fundus.
- Paracrine. This is histamine. It is already secreted by all parts of the stomach, is thrown into the intercellular fluid. Its action is local (only on neighboring cells). It also contributes to the secretion of hydrochloric acid of gastric juice (kills harmful microorganisms).
We pass to the next stage.
Intestinal stage
Recall that the whole process involves the stomach and duodenum. What does it mean? Food located in the upper parts of the small intestine (in particular, in the duodenum 12) continues to cause gastric secretion.
One feature - the secretion of gastric juice at this stage occurs in small quantities (about 10% of the total mass). The reason is seen in a small amount of gastrin, which can develop the mucous membrane of the duodenum.
Stimulation of gastric secretion during the intestinal phase occurs with the participation of long reflex arcs. At the same time, the inhibitory effect of peripheral sympathetic reflexes, duodenal hormones is noted. These include IPI, secretin, VIP, cholecystokinin and so on.
Inhibition of gastric secretion
Here, intestinal chyme is responsible for inhibition. I must say that it also slightly stimulates gastric secretion, but only at the beginning of the intestinal phase.
Inhibition will occur under the influence of two factors:
- Food located in the small intestine causes an enterogastric reflex. It is carried out through the internal nervous system of the intestine, the external parasympathetic and sympathetic nerves, designed to suppress gastric secretion. The reflex is triggered in response to a stretching of the small intestine, irritation of the mucosa, the presence of hydrochloric acid, and the breakdown products of proteins in the upper small intestine. It will be part of a complex mechanism that slows down the emptying of the stomach when filling with intestinal food.
- Fat, protein breakdown products, acid, hypoosmotic, hyperosmotic fluids and other irritating factors affecting the upper intestine cause the release of intestinal hormones. This is secretin, which in this case begins to suppress gastric function. Other hormones are somatostatin, an inhibitory gastric peptide, an intestinal vasoactive peptide. Their role is similar - to exert a moderate inhibition effect on the process of gastric juice production.
The secretion of gastric juice between meals
An interesting fact is that gastric secretion continues between meals. The glands will secrete several milliliters of juice every hour during the entire break between meals. That is, at a time when digestion in the organ is practically absent or very slightly.
The composition of the secret released in this case is also interesting. It practically does not contain hydrochloric acid. Its main composition is mucus, a small amount of pepsin.
But an increase in gastric secretion during this period is also possible. It is associated with emotional stimuli. Juice begins to stand out in volume up to 50 ml per hour, in it the content of pepsin and hydrochloric acid increases. Something this process will resemble the cerebral phase of gastric secretion. But with an important difference - food does not enter the stomach. Such activity of the body is fraught for a person with the development of peptic ulcers.
Gastric secretion occurs in three main phases - cerebral, gastric and intestinal. Each of them has its own regulatory mechanisms - stimulation and inhibition. Also, a slight secretion of gastric juice in a healthy person with special glands will be observed between meals.