Digestion is a complex multi-stage physiological process during which food (a source of energy and nutrients for the body), which enters the digestive tract, undergoes mechanical and chemical processing.
Digestion Features
Digestion of food includes mechanical (moistening and grinding) and chemical processing. The chemical process includes a series of successive stages of the splitting of complex substances into simpler elements, which are then absorbed into the blood.
This occurs with the obligatory participation of enzymes that accelerate the processes in the body. Catalysts are produced by the digestive glands and are part of the juices secreted by them. The formation of enzymes depends on what environment in the stomach, oral cavity and other parts of the digestive tract is established at one time or another.
After passing through the mouth, pharynx and esophagus, food enters the stomach in the form of a mixture of liquid and tooth-crushed solids. This mixture under the influence of gastric juice passes into a liquid and semi-liquid mass, which is thoroughly mixed due to peristalsis of the walls. Then it enters the duodenum, where it is further processed by enzymes.
The nature of the food determines what environment in the mouth and stomach is established. Normal in the oral cavity is slightly alkaline. Fruits and juices cause a decrease in the pH of the oral fluid (3.0) and the formation of an acidic environment. Products containing ammonium and urea (menthol, cheese, nuts) are able to lead the saliva reaction to alkaline (pH 8.0).
The structure of the stomach
The stomach is a hollow organ in which food accumulates, is partially digested and absorbed. The organ is located in the upper half of the abdominal cavity. If you draw a vertical line through the navel and chest, then approximately 3/4 of the stomach will be on the left of it. In an adult, the average stomach volume is 2-3 liters. When you consume large amounts of food, it increases, and if a person is starving, it decreases.
The shape of the stomach can change in accordance with its fullness of food and gases, as well as depending on the condition of neighboring organs: pancreas, liver, intestines. The shape of the stomach is also affected by the tone of its walls.
The stomach is an enlarged part of the digestive tract. At the entrance there is a sphincter (gatekeeper's gate) - portionwise passing food from the esophagus into the stomach. The part adjacent to the entrance to the esophagus is called the cardiac. To the left of it is the bottom of the stomach. The middle part is called the "body of the stomach."
Between the antrum (final) part of the organ and the duodenum is another pylorus. Its opening and closing is controlled by chemical irritants released from the small intestine.
Features of the structure of the wall of the stomach
The wall of the stomach is lined with three layers. The inner layer is the mucous membrane. It forms folds, and its entire surface is covered with glands (there are about 35 million in all), which secrete gastric juice, digestive enzymes intended for chemical processing of food. The activity of these glands determines which environment in the stomach - alkaline or acidic - will be established in a certain period.
The submucous membrane has a rather thick structure pierced by nerves and blood vessels.
The third layer is a powerful shell, which consists of smooth muscle fibers necessary for processing and pushing food.
Outside, the stomach is covered with a dense membrane - the peritoneum.
Gastric Juice: Composition and Features
The main role at the stage of digestion is played by gastric juice. Glands of the stomach are diverse in structure, but the main role in the formation of gastric fluid is played by cells secreting pepsinogen, hydrochloric acid and mucoid substances (mucus).
Digestive juice is an odorless, unpainted liquid that determines what environment should be in the stomach. It has a pronounced acid reaction. When conducting a study to detect pathologies, it is easy for a specialist to determine which environment exists in an empty (empty stomach) stomach. At the same time, it is taken into account that normal acidity of juice on an empty stomach is relatively low, but with stimulation of secretion it increases significantly.
In a person who adheres to a normal diet, 1.5-2.5 liters of gastric fluid are produced during the day. The main process in the stomach is the initial breakdown of proteins. Since gastric juice affects the secretion of catalysts in the digestion process, it becomes clear in which medium gastric enzymes are active - in acidic.
Enzymes produced by the glands of the gastric mucosa
Pepsin is the most important digestive juice enzyme involved in the breakdown of proteins. It is produced by the action of hydrochloric acid from its predecessor, pepsinogen. The effect of pepsin is about 95% of the digestive function of gastric juice. Actual examples speak of how high its activity is: 1 g of this substance is enough to digest 50 kg of egg white in two hours and stir 100,000 liters of milk.
Mucin (gastric mucus) is a complex complex of protein substances. It covers the gastric mucosa over the entire surface and protects it both from mechanical damage and from self-digestion, since it can weaken the effect of hydrochloric acid, in other words, neutralize it.
Lipase, an enzyme that breaks down fats, is also present in the stomach . Gastric lipase is inactive and mainly affects milk fats.
Another substance that deserves mention is the absorption of vitamin B 12 , Castle's intrinsic factor. Recall that vitamin B 12 is necessary for the transfer of hemoglobin in the blood.
The role of hydrochloric acid in digestion
Hydrochloric acid activates the enzymes of the gastric juice and promotes the digestion of proteins, since it causes their swelling and loosening. In addition, it kills bacteria that enter the body with food. Hydrochloric acid is released in small doses, regardless of what kind of environment the stomach has, whether it has food or is empty.
But its secretion depends on the time of day: it was found that the minimum level of gastric secretion is observed in the period from 7 to 11 in the morning, and the maximum - at night. When food enters the stomach, acid secretion is stimulated by an increase in vagus nerve activity, gastric distension, and the chemical effects of food components on the mucous membrane.
What environment in the stomach is considered standard, norm and deviations
Speaking about the environment in the stomach of a healthy person, it should be borne in mind that different parts of the body have different values of acidity. So, the highest value is 0.86 pH, and the minimum is 8.3. The standard indicator of acidity in the body of the stomach on an empty stomach is 1.5-2.0; on the surface of the inner mucous layer, the pH is 1.5-2.0, and in the depth of this layer is 7.0; in the final section of the stomach varies 1.3-7.4.
Diseases of the stomach develop as a result of an imbalance of acid production and neuolization and directly depend on what environment is in the stomach. It is important that the pH values are always normal.
Prolonged hypersecretion of hydrochloric acid or defective acid neutralization leads to an increase in acidity in the stomach. In this case, acid-dependent pathologies develop.
Reduced acidity is characteristic of hypoacid gastritis (gastroduodenitis), cancer. The indicator for gastritis with low acidity is 5.0 pH or more. Diseases mainly develop with atrophy of the cells of the gastric mucosa or their dysfunction.
Gastritis with severe secretory insufficiency
Pathology occurs in patients of mature and advanced age. Most often it is secondary, that is, it develops against the background of another disease preceding it (for example, a benign stomach ulcer) and is the result of what kind of environment in the stomach is alkaline, in this case.
The development and course of the disease is characterized by the absence of seasonality and a clear periodicity of exacerbations, that is, the time of their occurrence and duration are unpredictable.
Symptoms of secretory insufficiency
- Constant belching with a rotten aftertaste.
- Nausea and vomiting during exacerbation.
- Anorexia (lack of appetite).
- A feeling of heaviness in the epigastric region.
- Alternating diarrhea and constipation.
- Flatulence, rumbling and transfusions in the stomach.
- Dumping syndrome: a feeling of dizziness after ingestion of carbohydrate food, arising due to the rapid intake of chyme from the stomach into the duodenum, with a decrease in gastric activity.
- Weight loss (weight loss is up to several kilograms).
Gastrogenic diarrhea can be caused by:
- poorly digested food entering the stomach;
- a sharp imbalance in the process of digesting fiber;
- accelerated emptying of the stomach in violation of the closure function of the sphincter;
- impaired bactericidal function;
- pathologies of the pancreas.
Gastritis with normal or increased secretory function
This disease is more commonly seen in young people. It has a primary character, that is, the first symptoms appear unexpectedly for the patient, because before that he did not feel any expressed discomfort and subjectively considered himself healthy. The disease proceeds with alternating exacerbations and respite, without a pronounced seasonality. To determine the exact diagnosis, you need to see a doctor in order for him to schedule an examination, including an instrumental one.
In the exacerbation phase, pain and dyspeptic syndromes prevail. Pain, as a rule, is clearly related to the environment in the human stomach at the time of eating. Pain occurs almost immediately after eating. Less painful are the fasting late pains (some time after eating), a combination is possible.
Symptoms with increased secretory function
- The pain is usually mild, sometimes accompanied by pressure and heaviness in the epigastric region.
- Late pains are intense.
- Dyspeptic syndrome is manifested by belching of "sour" air, an unpleasant aftertaste in the mouth, impaired taste sensations, nausea, which relieves vomiting pain.
- Patients experience heartburn, sometimes painful.
- Intestinal dyspepsia syndrome is manifested by constipation or diarrhea.
- Usually expressed neurasthenic syndrome, characterized by aggressiveness, mood changes, insomnia and overwork.