Digestion of food is an important process that directly affects the vital activity of our body. The very first processing of food is still in the mouth. But its further path through the stomach will be important. This is what we will devote the article to. We will analyze the phases of gastric secretion, consider the mechanisms of its regulation and other important topics.
Four food groups by digestion speed
The duration of the assimilation of a particular food by our body is different. All food can be divided into four categories here:
- Carbohydrate food - digested the fastest.
- Protein food - takes an average time to digest.
- Fatty food (plus its combination with protein) is a product with a long absorption time.
- Category of food that is not absorbed by the body, or takes too long to digest.
Digestion time for each category
So how much food is digested in the stomach? Consider each category by time:
- 35-60minutes. 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 fatty), dried fruits, pre-soaked seeds and sprouts.
- 2-3 hours. Nuts, cereals, seeds, cereals, boiled legumes, mushrooms, baked goods and solid dairy products.
- About 4 hours (or not digested at all). The category includes: meat, fish, coffee or tea with milk, canned food, most pasta.
Water 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 the overall digestion of food looks like this:
- Stay food in the stomach - up to 4 hours.
- Digestion in the small intestine - 4-6 hours.
- The last step (digestion in the large intestine) can take up to 15 hours.
Phases of gastric secretion
So how is the processing of food eaten here? The following phases of gastric secretion are distinguished:
- Brain phase.
- Gastric stage.
- Intestinal stage.
What the stomach and duodenum do in their continuation, we will analyze in detail.
Brain Stage
This phase is activated before the ingested food enters the stomach. She is aroused by the smell, the taste, the sight of food, or even the thought of it. Howthe more appetite is played out, the more active the production of gastric juice by the body will be.
The brain phase is determined by nerve signals that originate in the cerebral cortex, the appetite centers of the hypothalamus and the amygdala. Further, these impulses are transmitted to the motor dorsal nuclei of the vagus nerve. From there (via 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. Starts in 5-7 minutes and lasts 1.5-2 hours.
The scheme of the reflex arc here will be as follows:
- Receptors in the mouth.
- Sensitive fibers of the brain, cranial centers.
- Vagus nuclei, medulla oblongata.
- Preganglionic nerve fibers.
- Ganglia.
- Postganglionic nerve fibers.
- Glands of the stomach responsible for 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 gastrointestinal tract, intestinal local reflexes, and the gastrin mechanism begin to be stimulated. Each of the listed elements causes the secretion of gastric juice within a few hours that the food is in the stomach.
The volume of secretion released during this phase will equal 70% of the total mass. Therefore, forThe gastric stage is responsible for the majority of all juice produced. Its total volume per day is approximately 1500 ml. During the phase, the hydrochloric acid of the gastric juice kills the harmful microorganisms contained in the food.
The following mechanisms will be involved at this stage:
- Nerve central. There are long reflex arcs. The path is as follows: gastric receptors - sensory pathways - vagus nuclei (medulla oblongata) - preganglionic nerve fibers - ganglia - intramural - postganglionic nerve fibers - gastric glands responsible for secretion production.
- Nervous locals. These include short reflex arcs that will close in the walls of the stomach itself.
- Endocrine. What stands out here? Gastrin, which is released into the blood by the endocrine cells of the gastric pylorus. It stimulates the secretion (excretion) of hydrochloric acid by the glands of the fundus.
- Paracrine. It's 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). Also promotes the secretion of hydrochloric acid in the stomach (kills harmful microorganisms).
Go to the next stage.
Intestinal stage
Recall that the stomach and duodenum are involved in the whole process. What does it mean? Food in the upper small intestine (particularly the duodenum) continues to trigger gastric secretions.
One feature is highlightinggastric 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 GIP, secretin, VIP, cholecystokinin, etc.
Inhibition of gastric secretion
Intestinal chyme is responsible for inhibition here. It must be said that it also slightly stimulates gastric secretion, but only at the beginning of the intestinal phase.
Braking will occur under the influence of two factors:
- Food in the small intestine causes an enterogastric reflex. It is carried out through the internal nervous system of the intestine, external parasympathetic and sympathetic nerves, designed to suppress gastric secretion. The reflex is triggered in response to stretching of the small intestine, irritation of the mucous membrane, the presence of hydrochloric acid, protein breakdown products in the upper sections of the small intestine. It will be part of a complex mechanism that slows down the emptying of the stomach when the intestines are filled with food.
- Fat, protein breakdown products, acid, hypoosmotic, hyperosmotic fluids and other irritants that act on 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, gastric inhibitory peptide, intestinal vasoactive peptide. Their role is similar - to have a moderate inhibitory effect on the production of gastric juice.
Emission 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, during the period when digestion in the body is practically absent or very insignificant.
The composition of the secret allocated 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 up to 50 ml per hour, it increases the content of pepsin and hydrochloric acid. In some ways, 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 organism is fraught for a person with the development of a peptic ulcer.
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 he althy person by special glands will be observed between meals.
