Stages of the motor function of the stomach. Motor function of the stomach. Causes of motor disorders
The stomach functions as a depot, where not only the hydrolysis of nutrients occurs, but also the accumulation of chyme - up to 3 liters, which gradually passes into the duodenum from the pylorus due to the propulsive contraction of its smooth muscles. The following stages of regulation of motor function of the stomach can be distinguished:
1 "Receptive relaxation" of the stomach- if food enters its cavity, the proximal part - the bottom and body - relax, adapting the volume of the stomach to a slight increase in pressure. This is accomplished thanks to the weight-vagal reflex, because after sectioning the vagus, relaxation does not occur. Cholecystokinin-pancreozymin (CCK-PZ) is also involved in receptive gastric relaxation and goalie contraction.
2 Mixing stomach contents is carried out due to the contraction of the muscles of its distal section as follows:
Slow waves of smooth muscle depolarization occur at a frequency of 3-5 per minute. When the threshold value of depolarization is reached, APs are generated, which leads to muscle contraction (Fig. 13.20)
The wave of muscle contraction moves in the distal direction of the pyloric stomach - antral systole. In this case, the contents of the stomach slowly move with gastric juice. Following this, peristaltic waves (their amplitude and speed of propagation) intensify, as a result of which the chyme is pushed towards the exit from the stomach;
Gastric contractions increase with activation of the vagus nerve and decrease with activation of sympathetic influences.
3 Evacuation of stomach contents is carried out by coordinated sequential reflex contractions of the antrum and pylorus, increasing pressure in the pylorus to 10-25 cm of water. Art., by opening the gatekeeper (gatekeeper), due to which a portion of chyme enters the duodenum. The contraction of the pyloric sphincter, which then occurs under the influence of the local duodenogastric reflex, prevents the return of chyme.
The time for evacuation of mixed food from the stomach is 6-10 hours.
Other factors also influence the speed of evacuation:
■ a positive pressure gradient between the stomach and duodenum, sufficient for the passage of gastric contents,
■ fats move into the duodenum and suppress evacuation due to prolonged contraction of the pyloric sphincter under the influence of CCK-PZ secreted in it;
■ ions+, entering the duodenum with chyme, suppress evacuation through the mechanism of the local duodenogastric reflex, which leads to contraction of the pyloric sphincter;
■ isotonic chyme is evacuated faster than hypertonic chyme.
Hungry stomach contractions occur every 90 minutes when the stomach is empty, due to the pacemaker activity of myocytes that form migratory motor complex(MMK) - cycles of motor activity migrating from the stomach to the distal ileum. In the stomach, such a pacemaker is located on the lesser curvature in the proximal part of its body. From here, the contraction spreads towards the pylorus of the stomach, which helps relieve it of food debris. The main regulator of MMK is the hormone motilin- a polypeptide that is produced by ECL cells and Mo cells of the stomach. Its concentration increases 100 times in the mid-grass period every 90-100 minutes. In case of introduction motilina contractions of the smooth muscles of the stomach and intestines occur.
RICE. 13.20. Balonographic recording of the motor activity of the dog's stomach. I - hungry: A - period of physical activity; B - rest period. II - peristaltic types of contractions of the fundic part of the stomach during food activity: 1 - weak; 2 - strong; 3 - tonic
Absorption in the digestive tract.
Absorption is the process of transfer of substances from the gastrointestinal tract into the blood and lymph through cells, their membranes and intercellular passages.
It occurs throughout the gastrointestinal tract, but in its different parts with different intensities.
The oral mucosa is capable of absorption, but the oral cavity usually does not contain the end products of nutrient breakdown. Some medicinal substances are well absorbed here.
Water, mineral salts, monosaccharides, drugs, alcohol, and very few amino acids are absorbed in the stomach.
The main absorption process occurs in the small intestine.
Carbohydrates absorbed into the blood in the form of glucose and other monosaccharides.
Squirrels enter the blood in the form of amino acids. Neutral fats are broken down by enzymes into glycerol and fatty acids. Glycerin is soluble in water, so it is easily absorbed. Fatty acids are absorbed only after interaction with bile acids, with which they form complex compounds. Fats enter mainly the lymph and only 30% into the blood.
Absorption of water and mineral salts occurs in the large intestine.
Suction mechanisms.
Passive transport (diffusion, filtration).
Active transport with the participation of carrier enzymes.
Chewing– done reflexively. Food in the mouth irritates the receptors, from which signals are transmitted through the afferent fibers of the trigeminal nerve to the chewing center (medulla oblongata). As a result, the food is crushed, in addition, it is mixed with saliva and a food bolus is formed.
Swallowing- a reflex act, its center is located in the medulla oblongata. There are 3 phases in the swallowing process:
1. Oral (arbitrary). The bolus of food is moved to the back of the tongue by movements of the tongue and cheeks, then successive contractions of the muscles of the tongue of the anterior, middle and posterior groups move it to the root of the tongue.
2. Pharyngeal (fast involuntary. Irritation of the receptors of the mucous membrane of the root of the tongue reflexively causes contraction of the muscles that lift the soft palate, the muscles of the tongue and the muscles that lift the larynx. Pressure increases in the oral cavity, so food moves into the pharynx. Then the muscles of the pharynx above the food bolus begin to contract and it moves to the esophagus , the pressure in the pharynx increases, the pharyngeal-esophageal sphincter opens and food passes into the esophagus.
3. Esophageal (slow involuntary). The passage of food through the esophagus occurs due to successive contractions of the circular muscles in the wall of the esophagus. They have the character of a wave that arises in the upper part of the esophagus and spreads towards the stomach. This type of contraction is called peristaltic. Regulation of motor activity is carried out by the autonomic nervous system: the parasympathetic vagus nerve enhances peristalsis of the esophagus and relaxes the cardiac sphincter at the border with the stomach, sympathetic nerves inhibit peristalsis and increase the tone of the cardiac sphincter.
Motor function of the stomach.
Provided by the work of smooth muscles. There are 3 types of motor activity in the stomach:
1. Peristaltic movements occur due to contractions of the circular muscles. The contraction wave begins in the region of the cardial region of the stomach and goes to the pyloric sphincter. Wave frequency -3 times per 1 min.
2. Systolic contractions are muscle contractions in the pyloric region of the stomach. They ensure the passage of chyme into the duodenum.
3. Tonic contractions are caused by changes in muscle tone in different parts of the stomach. As a result, the food mass is mixed with digestive juice and moves to the exit from the stomach.
The parasympathetic nervous system enhances motor skills, the sympathetic nervous system inhibits. Humoral factors that enhance motility: insulin, gastrin, histamine. Humoral factors inhibiting gastric motility: enterogastrin, cholecystokinin, adrenaline, norepinephrine.
In addition to the named types of contractions in the stomach, there are antiperistalsis, which occurs with vomiting.
The passage of food from the stomach to the intestines.
Food stays in the stomach for 6 to 10 hours. During this time, the smooth muscle in the wall of the stomach contracts, the contents of the stomach are mixed with gastric juice, moves towards the exit into the small intestine and exits into the duodenum.
Chyme enters the duodenum in portions from the pyloric section of the stomach. There is a sphincter at the border between the stomach and duodenum. The hydrochloric acid of the gastric juice irritates the receptors of the gastric mucosa in the pyloric region, the sphincter opens, the muscles in the wall of the pyloric region contract and the chyme passes into the duodenum. Here the reaction of the environment is slightly alkaline, so the acid present in the chyme acts on the mucous membrane of the duodenum, the sphincter contracts and the evacuation of chyme from the stomach into the intestines stops. When the reaction of the environment in the intestine is restored, the process is repeated.
Motor function of the digestive tract. The process of absorbing food, chewing it, swallowing it, and moving food contents along the digestive tract is associated with this function. This function helps mix food with digestive secretions. It is necessary for absorption and for the removal of indigestible residues. To study the model of the digestive tract, different methodological approaches are used.
Balloon kinetomography. Insertion of a balloon into the digestive canal connected to a monometer using a tube system. In humans, the X-ray method of examination with preliminary administration of barium sulfate is widely used.
The electrogastrography method is used, based on the registration of electrical impulses. The experiment uses contractions of isolated sections of the digestive tract and visual observation.
In humans, the method of auscultation is also used - listening to sounds associated with motor skills.
In children, the motor function also includes the act of sucking. After placing food in the oral cavity, chewing begins. Chewing consists of a reflex movement of the lower jaw in relation to the upper jaw. The masticatory muscles include: the masseter proper, digastric, temporal, superior and inferior pterygopalatine.
When opening the mouth, the proprioceptors of the masticatory muscles are irritated, and at the same time, a reflexive contraction of the masticatory muscle itself, and the temporal, pterygopalatine muscles occurs.
If food is in the oral cavity, it irritates the receptors of the mucous membrane, this causes contraction of the digastric muscle, which helps lower the lower jaw. In addition, it lowers due to gravity.
The chewing function makes it easier to swallow food, destroys the cellulose shell of fruits and vegetables, increases the area of contact with digestive enzymes, promotes mixing and wetting of food with saliva, and creates better contact with taste buds. Chewing helps release the smell of food. The smell affects the olfactory receptors, and this increases the pleasure of eating.
As a result of chewing, a food bolus is formed, which is swallowed.
600 acts of swallowing occur per day. 200 during meals, 350 at other times, 50 at night.
The act of swallowing is divided into a voluntary phase (before food moves to the root of the tongue). When the food bolus passes behind the root of the tongue, the involuntary phase of the act of swallowing begins. Food irritates the sensory receptors in the oral cavity formed by the trigeminal nerve. Taste buds that are associated with the 7th pair, and the back third with the 9th pair. The vagus also takes part in sensory innervation. From these receptors, sensory impulses go to the swallowing center. And from there, along the motor fibers of these same nerves, a coordinated muscle contraction occurs, during which the soft palate rises and closes under the nasopharynx. The trachea and hyoid bone rise, the epiglottis descends and this closes the entrance to the airways. The root of the tongue rises, presses against the palate and prevents the food bolus from returning to the oral cavity.
The pharyngeal phase of swallowing begins. Contractions of the pharynx push the bolus toward the esophagus. At the border of the pharynx and esophagus is the upper esophageal sphincter. It occupies a segment 3 centimeters long. When the muscles of the pharynx contract, the upper esophageal sphincter opens. Thus, the food bolus enters the esophagus, through which the next, esophageal phase of the act of swallowing occurs. The movement of the bolus of food through the esophagus is associated with the muscles of the esophagus. In the upper third it will be the striated muscle. And the lower ones are smooth. There are circular and longitudinal muscles.
The speed of movement of the food bolus is 4-5 cm per second. Solid food passes the esophagus in 8-9 seconds. In this case, high pressure is created inside the esophagus (from 30 to 120 mm).
If a person consumes liquid food, then the muscle tone of the esophagus decreases and a lumen is created through which a column of liquid enters. This process lasts 1-2 s.
At the transition of the esophagus to the stomach there is a cardiac sphincter. He is in a state of tonic tension. The tone of the sphincter is maintained due to nervous and hormonal influences (gastrin, cholicytokenin, matenin). The pressure created by the sphincter is 10-15 mm. As the food bolus approaches the sphincter, it relaxes. This allows the food bolus to pass into the stomach. Simultaneously with the relaxation of the cardiac sphincter, the tone of the stomach muscles relaxes. Receptive relaxation. The esophageal muscles are innervated by the vagus nerve, which promotes motility, but the vagus does not cause sphincter relaxation. With high muscle tone of the esophagus, a condition of acolosia may occur, when food is retained in the lower part of the esophagus and causes expansion of this part.
Reflux is the reflux of stomach contents into the esophagus. This condition is accompanied by a feeling of heartburn. If this happens frequently, ulceration of the esophagus may occur. If the sphincter is insufficient, aerotopia may occur - swallowing air with food. This is especially evident in infants during sucking. Therefore, the baby should not be immediately placed in a horizontal position after sucking, because this will promote regurgitation.
Motility of the stomach. The motor function of the stomach is related to the function of smooth muscles. Located in three directions: circular, longitudinal and oblique. The stomach is separated from the esophagus. The outlet of the stomach is separated from the duodenum by the pyloric sphincter. The functional prepyloric sphincter is also isolated. The smooth muscles of the stomach receive innervation from the vagus nerve and the sympathetic nerve. In addition, the stomach has local innervation due to the submucosal and amuscular plexus. In this case, cells of the first type can perform an excitatory function. The motility of the stomach is represented by tonic contractions of smooth muscles, wave-like peristaltic contractions, and smooth muscles also have the property of automaticity. Individual smooth muscle cells are connected to each other using tight electrical contacts, which allows the smooth muscles to function as a functional sentidium. Motor activity in the stomach is observed during digestion. But contractions in the stomach are also observed without food. This type of motor activity is called hunger-periodic motor activity.
During the first meal, a decrease in stomach tone occurs. This will be a receptive relaxation of the stomach muscles, which creates reservoirs for food to be placed in the stomach. In this case, each subsequent food bolus falls into the center of the previous one, due to which the contents of the stomach become layered.
After the act of eating ends, there is a gradual increase in the tone of the stomach muscles. As the tone of the stomach muscles increases, peristaltic contractions begin to appear. Motor function is expressed differently in different parts. In the proximal part (includes the bottom and upper third) tonic contractions are better expressed. And the distal part, which includes the lower third, has a greater ability for wave-like contractions. Gastric motility helps place food in the stomach, grind food inside the stomach, and mix with gastric juice.
The main rhythm is 3 contractions per minute. Moreover, peristaltic waves can travel at a speed of 0.3 to 4 contractions. At the beginning, peristalsis in the stomach is not deep. More frequent contractions are observed. As the peristaltic wave advances, its strength increases towards the pyloric region. At this stage, mixing and mechanical processing occur. As contractions intensify, the rhythm decreases and the peristaltic waves become more powerful. Some of the digested food is pushed through the pyloric sphincter into the duodenum. But particles no more than 1 mm in diameter can pass into the duodenum. Entering the intestine causes a powerful contraction of the pyloric sphincter and contraction of the pyloric region. In this case, the contents are thrown into the body of the stomach. The return of contents to the body of the stomach is retropulsation. With this reverse movement, further fragmentation of particles occurs.
The process of evacuation of food from the stomach will be determined by the coordinated work of the muscles of the stomach and the digestive sphincter. The transition process will be influenced by the volume of gastric contents, the chemical composition and calorie content of food, consistency, degree of acidity and osmotic concentration. In order for the contents of the stomach to pass into the duodenum, it must be liquid or semi-liquid. It must also have isotonic pressure and a certain degree of acidity. When food enters the 12-type intestine, irritation of mucosal receptors occurs. Irritants can be fatty acids, osmotic pressure, etc. When irritated, the obturator reflex occurs, which consists of closing the pyloric sphincter and weakening gastric motility.
The accelerated flow of food from the stomach into the intestines leads to dumping syndrome, which is characterized by the appearance of severe weakness, dizziness, and the desire to lie down after eating.
In the fasting state, periodic contractions appear in the stomach (migrating myoelectric complex). Occurs every 90 minutes and lasts 3-5. The migratory complex manifests itself not only in the stomach, but also in the small intestine. The significance of these contractions is due to the fact that the mucous membrane is freed from mucus, food debris and dead cells. These contractions coincide with the feeling of hunger.
Periodic hungry motor activity is associated with the feeling of hunger in the hypothalamus. It is felt as a change in the blood (the level of glucose, calcium decreases, the appearance of choline-like substances).
The impulses are sent to the cerebral cortex. At the same time, there is an impact on the underlying departments.
Motor function of the small intestine. The wall of the small intestine has an external longitudinal and internal circular. There are tonic contractions, rhythmic segmentation, pendulum-shaped contractions and peristaltic contractions. Rhythmic segmentation manifests itself in the rhythmic contractions of the circular muscles. At the same time, it is segmented into separate sections.
Pendulum-like contractions involve not only circular muscles, but also longitudinal ones. Contraction of circular muscles causes contraction, and longitudinal muscles cause expansion.
The frequency of contractions in the upper sections is 10-12 per minute. And in the lower sections there will be 5-8. Peristalsis is needed to move the contents of the small intestine distally.
With slow contraction, the speed is equal. With rapid peristalsis, the speed reaches 7-21 cm.
Motility of the small intestine depends on the composition of food. Rough food stimulates motor skills. Fatty foods also enhance motor skills. Serotonin, histamine, gastrin, methylin, cholicystekinin, substance P, vasopressin and bile stimulate. Inhibitors include gastroinhibitory and vasointerstinal. The motor function of the small intestine is controlled by the intercal part of the autonomic nervous system.
The contents of the small intestine flow in only one direction. Antiperistaltic contractions are observed only during vomiting.
Contractions begin 1-4 minutes after eating, every 30-60 s the sphincter reflexively expands and the contents flow from the small intestine into the cecum. The work of this sphincter occurs due to the gastroiliocytic reflex. These two areas are connected to each other.
When food enters the large intestine, approximately the same pattern of motor activity is observed in the large intestine as in the small intestine, but the movements are much slower. In addition, antiperistaltic contractions are also present here. Therefore, during the motor function, the contents slowly move in one direction or the other. This facilitates the absorption of water and the formation of feces. Small amounts of nutrients are absorbed. Approximately 3-4 times a day, propulsive contractions of the colon occur, which push the contents in the distal direction. Regulation of colon motility is carried out by local plexuses, as well as parasympathetic and sympathetic nerves. Formed feces are collected in the distal part of the colon, not reaching the rectum.
In humans, the urge to defecate occurs when feces enter the rectum. The first sensations occur when the pressure in the rectum increases to 18 mm Hg. There are 2 sphincters in the rectum. Internal (smooth muscles) and external (striated muscles). Both sphincters are in a state of tonic contraction. The tone of the sphincters is controlled by the sacral division of the parasympathetic system. The spinal center is also connected with the overlying centers. But the centers of the brain mainly have an inhibitory effect. The activity of these centers allows for voluntary regulation of the act of defecation. When the mucous membrane is irritated, a reflex increase in the activity of the parasympathetic centers occurs, which enhances peristalsis and relaxes the internal sphincter.
The defecation reflex increases after eating. Suppression of this reflex can lead to impaired patency. Voluntary regulation is established at the 2nd year of life. When the spinal cord is damaged above the sacral region, the defecation reflex occurs periodically, but involuntarily. Damage to the sacral region leads to relaxation of the sphincter.
Main didactic elements of the topic: Types and characteristics of gastric motility during digestion. The mechanism of evacuation of acidic gastric chyme. Mechanisms of regulation of motor activity of the stomach. Types of small intestinal motility and their regulation. Characteristics of motor functions of the large intestine. Physiological significance of periodic hungry activity of the digestive tract. Food motivation. Physiological bases of hunger and satiety.
Motor function of the digestive organs consists in the contractile activity of the striated and smooth muscles of the digestive tract, which contributes to the grinding of food, its mixing with digestive secretions and movement from the oral region in the distal (caudal) direction.
The motor function of the gastrointestinal tract is based on the contractile activity of smooth muscle cells. They make up three layers: outer longitudinal, medium circular, internal longitudinal.
The main feature of smooth muscle cells of the gastrointestinal tract is their automatic – the ability to spontaneously excite and contract in the absence of external irritating factors.
Automation is the basis of all types of motor (motor) activity of the gastrointestinal tract, which include:
tonic waves,
peristalsis,
antiperistalsis,
systolic contractions,
rhythmic segmentation,
pendulum-like contractions.
The act of chewing leads to a reflex increase in the tone of the stomach. But during swallowing it occurs receptive relaxation - reflex relaxation of the smooth muscles of the stomach.
After filling the stomach, thanks to the great plasticity of its muscles and increased tone when they are stretched, food is tightly enveloped by the gastric walls. In a stomach filled with food, three types are observed motor activity :
1) tonic waves,
2) peristalsis,
3) systolic contractions.
Tonic waves – these are high-amplitude, long-lasting and slowly spreading contractions, which are caused by the redistribution of muscle tone. Tonic contractions of the filled stomach contribute to further grinding, mixing and compaction of food coming from the oral region.
Peristalsis - this is a wave-like spreading contraction of circular smooth muscle fibers proximal to the chyme, and longitudinal ones distal to it.
The main function of peristalsis is the creation of a proximodistal pressure gradient, which ensures mixing and movement of chyme in the distal (caudal) direction. This is due to the narrowing of the gastric lumen with contraction of the circular muscles proximal to the chyme and the expansion of the gastric cavity distal to it. The resulting proximodistal pressure gradient is the direct cause of the advancement of chyme in the caudal direction.
Peristaltic waves occur nearby cardiac section of the stomach located at the lower end of the esophagus. They spread towards pyloric (antral) section adjacent to the duodenum. The speed of propagation of the peristaltic wave increases from 1 cm/s in the cardiac region to 3-4 cm/s in the pyloric region. Due to this, the pyloric region contracts as a single functional formation - observed systolic contraction.
Due to systolic contraction of the gastric antrum and relaxation of the smooth muscle of the pyloric sphincter (smooth muscle valve), a proximodistal pressure gradient occurs. A portion of acidic gastric chyme, along the gradient of this pressure, enters the duodenum for further processing.
In the duodenal bulb, acidic gastric chyme irritates mechano- and chemoreceptors. It causes inhibitory enterogastric reflex – inhibition of the motor-evacuation function of the stomach and contraction of the smooth muscles of the pyloric sphincter, which ensures discrete evacuation of gastric chyme and prevents its return to the stomach.
The mechanisms regulating the motor function of the stomach are divided into enteral (local) And extrainternal. Local enteral mechanisms regulations are divided into nervous And humoral. They are provided by the reflex activity of the enteric metasympathetic nervous system and gastrointestinal hormones of the diffuse endocrine system.
Extraenteric mechanisms regulation of the motor function of the stomach is carried out with the help of peripheral And central reflexes. Reflex influences arise from irritation of the receptors of the mouth, pharynx, esophagus, interoreceptors of the gastrointestinal tract and are transmitted to the smooth muscles of the stomach using efferent fibers of the vagus and sympathetic nerves.
Excitation of the nerve fibers of the vagus nerves increases the strength and frequency of contractions of the stomach, increases the speed of propagation of peristaltic waves. At the same time, the vagus nerve relaxes the pyloric sphincter and is involved in providing receptive relaxation of the stomach. This is due to the switching of excitation in the intramural ganglia to peptidergic neurons in the endings of which inhibitory mediators - VIP and ATP - are released.
Excitation of sympathetic nerve fibers has an inhibitory effect on gastric motility: the frequency and strength of contractions decreases, and the speed of propagation of peristaltic waves decreases. At the same time, sympathetic influences ensure contraction of the pyloric sphincter.
The higher parts of the central nervous system - the hypothalamus, limbic system and cerebral cortex - are involved in the regulation of the motor function of the stomach. The central nervous system as a whole has an inhibitory effect. Therefore, with complete denervation, gastric motility increases significantly. The experience of fear and pain, increased psycho-emotional stress cause inhibition of motor skills. However, strong and prolonged negative emotions lead to its intensification.
Further mechanical processing, mixing of chyme with alkaline digestive secretions and its movement in the distal direction is ensured by the motor activity of the small intestine.
The main types of small intestinal motility are:
tonic waves,
peristalsis,
rhythmic segmentation,
pendulum-like contractions.
Tonic contractions of the small intestine can be local or move at low speed. They are superimposed rhythmic And pendulum-shaped abbreviations.
Rhythmic segmentation - this is an alternating contraction and relaxation of circular smooth muscle fibers of the intestine, which occur simultaneously in several neighboring areas. Pendulum-like movements - this is an alternating contraction and relaxation of the longitudinal smooth muscle fibers of the intestine, which occur simultaneously in several adjacent areas.
The main functions of rhythmic segmentation and pendulum-like movements are mixing, grinding and compaction of the intestinal chyme, which is due to its reciprocating movements.
Prevails in the regulation of small intestinal motility local enteral mechanisms: myogenic, nervous And humoral.
Myogenic mechanisms associated with the ability of smooth muscle cells of the small intestine to contract spontaneously or respond to contraction when stretched. Myogenic regulation is complemented by the reflex activity of the enteric metasympathetic nervous system and the influence of gastrointestinal hormones.
Extraenteric reflex influences are caused by irritation of the receptors of the esophagus and interoreceptors of the gastrointestinal tract. They are transmitted to the smooth muscles of the small intestine using efferent fibers of the vagus and sympathetic nerves.
Excitation of parasympathetic fibers of the vagus nerves enhances the motility of the small intestine. Excitation of the sympathetic fibers of the splanchnic nerves has an inhibitory effect.
The higher parts of the central nervous system can have both an activating and an inhibitory effect, depending on the initial functional state of the small intestine. However, in general, the central nervous system has an inhibitory effect on the motor activity of the small intestine.
From the small intestine, portions of alkaline intestinal chyme enter the large intestine through the ileocecal sphincter. The peristaltic wave of the small intestine causes a reflex opening of the ileocecal sphincter and the entry of alkaline chyme along the proximodistal gradient into the large intestine. An increase in pressure in the colon increases the tone of the ileocecal sphincter muscles, which means it inhibits further flow of contents from the small intestine.
The entire process of digestion in humans lasts 1-3 days, of which the largest part of the time is spent moving through the large intestine. Chyme begins to enter the large intestine within 3-3.5 hours after eating, its filling lasts about 24 hours, and complete emptying occurs after 48-72 hours.
The main types of contractions of the large intestine are:
tonic contractions,
peristalsis,
antiperistalsis,
rhythmic segmentation,
pendulum-like contractions.
A specific type of motility of the large intestine is antiperistalsis – a wave-like spreading contraction of circular smooth muscle fibers of the intestine distal, and longitudinal ones proximal to the intestinal chyme. The main function of antiperistalsis is the creation of a disto-proximal pressure gradient, which ensures the return of intestinal chyme 15-20 cm to the proximal parts of the large intestine for additional processing and absorption of water.
When a sufficient amount of dense content accumulates in the transverse colon, strong propulsive peristaltic contractions colon, which are called mass contractions. During such waves, which occur 3-4 times a day, the contents of large areas of the colon are expelled into the sigmoid and rectum.
The leading role in the regulation of colon motility belongs to local mechanisms regulation – myogenic, nervous And humoral.
Extraenteric the effects are caused by irritation of the receptors of the mouth, pharynx, esophagus and interoreceptors of the gastrointestinal tract. They are transmitted to the smooth muscles of the large intestine using efferent fibers of the vagus, pelvic and splanchnic nerves. Excitation of parasympathetic fibers has an activating effect on colon motility, and sympathetic fibers have an inhibitory effect.
In the activity of the digestive system, regular periodic changes in motor and secretory activity are observed that are not associated with food intake. Periodic extra-digestive increase in the motor and secretory activity of the digestive organs is called periodic fasting activities. In the process of periodic fasting activity, a distinction is made between a period of work and a period of rest. In humans, periodic activity cycles consist of 20-minute periods of increased activity and 70-minute periods of relative rest.
Physiological significance of intermittent fasting activity:
satisfying the plastic and energy needs of the body due to the hydrolysis of proteins and enzymes released in the digestive juices,
excretion by the digestive glands of metabolic products to be excreted from the body,
preventing the spread of resident microflora throughout the small intestine in the proximal direction
participation in the formation of a state of hunger.
Intermittent fasting affects the body as a whole. During work, the heart rate increases, the blood supply to the digestive organs increases, the content of glucose and a number of enzymes in the blood increases, and the number of red blood cells and leukocytes in the blood increases.
Hunger as a physiological state serves as an expression needs(needs) the body to replenish its reserves of nutrients. Nutritional requirement - This is a decrease in the level of nutrients in the internal environment of the body caused by metabolic processes.
A decrease in nutrient content leads to stimulation of chemoreceptors in blood vessels and tissues. Information from peripheral chemoreceptors enters the digestive center - a set of neurons located on different floors of the central nervous system and regulating the secretory, motor and absorption functions of the digestive tract.
Its main leading structure is the hypothalamic region. In the lateral parts of the hypothalamus there is hunger center, and in the ventromedial ones - saturation center. Neurons of the lateral and ventromedial hypothalamus function according to trigger principle- excitation in these cells occurs periodically when their excitability reaches a certain critical level.
To excite the hunger center, the integration of three types of signals is necessary:
1) nervous afferentation, which comes from the mechanoreceptors of the gastrointestinal tract to the center of digestion as chyme is evacuated into the duodenum,
2) nerve afferentation from peripheral vascular chemoreceptors, which signal a decrease in the concentration of nutrients in the blood,
3) humoral afferentation caused by irritation of central hypothalamic chemoreceptors.
As chyme is evacuated from the stomach, irritation of the mechanoreceptors of the duodenal mucosa increases.
The signals that come from these mechanoreceptors to the hunger center cause an increase in its excitability and lead to a reflex deposition of nutrients. From the blood they enter the liver, striated muscles of the locomotor system and adipose tissue. Blood that loses its nutrients is called "starved." Irritation by “hungry” blood of peripheral chemoreceptors localized in the vascular bed and central receptors located in the hypothalamus causes excitation of the hunger center - the transformation of nutritional need into motivation (urge to action) occurs.
Food motivation- this is an emotionally charged arousal caused by nutritional need, selectively uniting the nervous elements of various floors of the central nervous system to form purposeful behavior leading to the satisfaction of the body’s need to replenish its reserves of nutrients.
A subjective manifestation of food motivation is feeling of hunger, which is reinforced by a negative emotion that encourages the search and consumption of food.
In conditions of no food entering the gastrointestinal tract, the body is able to maintain the relative constancy of its internal environment and the stability of physiological functions for some time (20-30 days) due to its own reserves of nutrients. However, their reserves are not unlimited. Therefore, a person is forced to periodically consume food.
Saturation during food consumption consists of two phases: 1) sensory saturation, 2) metabolic (true) saturation.
Primary (sensory )saturation develops within 15-20 minutes as a result of the action of food on the receptors of the oral cavity, esophagus and stomach, which leads to a reflex release of nutrient reserves from the depot into the blood. Nutrients excite neurons in the satiety center of the ventromedial hypothalamus, which inhibit the hunger center. Sensory saturation allows you to finish eating long before the formation and absorption of nutrients occurs in the digestive tract.
Only 1.5-2 hours after finishing a meal, when nutrients begin to flow from the gastrointestinal tract into the blood, does it occur? secondary (metabolic )saturation, which leads to the replenishment of depleted nutrient reserves.
As nutrients are consumed and a new nutritional need is formed, this entire cycle is repeated again and again.
Food is a vital necessity for humans. Its usefulness, timely supply in sufficient quantities ensures the normal functioning of the entire body, emotional state and performance. The functions of the stomach play a primary role for these purposes.
In order to understand how the stomach works, it is necessary to become familiar with its anatomy, the structure of cellular structures, and the muscle layer. Knowledge of physiology helps to find the right approach in the treatment and prevention of certain diseases not only of the stomach, but also of the entire digestive tract.
The stomach is a hollow, muscular organ, lined from the inside with a mucous membrane with a secretory and enzymatically active layer. It is one of the key organs of the gastrointestinal tract, where deep processing of food with enzymes and gastric juice occurs, digestion of the food bolus, from which nutrients are absorbed into the blood. Then, with the help of contractile, translational movements - motility, the food bolus moves further into the intestine, where the final stage of processing and the formation of feces occurs.
Digestion begins in the mouth, where food is chewed and first processed by enzymes. Then through the esophagus it enters the cavity of the stomach, which is divided into three sections:
- cardiac;
- fundal;
- gatekeeper.
The cardiac region has a sphincter that opens when food enters the vestibule of the stomach. After the lump penetrates inside, it tightly closes the hole, preventing stomach acid from entering the lower parts of the esophagus.
The fundus is the main area of the organ, which is equipped with a secretory layer on the mucous membrane. When food enters, the secretion of hydrochloric acid, gastrokinetics, is activated, which stimulate the peristaltic movements of the stomach.
The pylorus or antrum is the final transition of the stomach into the duodenum. Digested food, moving through the stomach cavity, stimulates the opening of the pyloric sphincter to exit it into the duodenal lumen.
A very important point at this stage is the complete closure of the pyloric valves to prevent the reflux of bile into the stomach cavity. If there is an inferiority or defect in the sphincter due to operations, regular overeating or other reasons, then bile can corrode the walls of the stomach, gradually leading to the development of erosive gastritis, then to an ulcer.
The muscular layer of the stomach is smooth muscle that does not obey human will, and contractions and movements occur only on the basis of natural mechanisms. This is why it is important to understand the structure of the organ, because you cannot consciously force the stomach to contract if its physiological mechanisms are damaged or lost.
Cells that have enzymatic and secretory activity are also susceptible to damaging effects. Inadequate production of enzymes due to external influences, internal causes, and age-related changes leads to insufficient functions of the human stomach.
Digestive functions
It is clear that the main task of the stomach is to digest food and move it further. But this is too general a concept; this approach does not allow one to correctly diagnose, treat and develop measures to prevent his diseases. The stomach performs the following digestive functions:
Each of them is necessary for complete digestion, providing the body with vitamins and building materials. Good digestion, absorption and promotion of food is especially important for newborn children, who are just establishing the functioning of the body, so the closest attention should be paid to baby nutrition and health.
During pregnancy, taste preferences change, a complete restructuring of all organs and systems occurs, so the insufficiency of any of the functions can affect the health of the unborn baby or mother.
Depositing
The translation from Latin means “accumulation”, that is, food lingers in the stomach for some time. This is necessary to ensure that all nutrients are properly processed, blood flows to the walls of the organ, and the process of digesting food takes place as expected. If there were no mechanism for delaying the food bolus inside the stomach for several hours, then it would fall further without mixing with the enzymes and hydrochloric acid contained in the gastric juice.
The depositing function of the human stomach is ensured due to the mechanism of reflex relaxation of the muscular apparatus of the fundus. The chyme (food bolus) is retained for quite a long time: from 3 to 10 hours, depending on the density of the incoming food.
Motor
This is a whole series of types of motor mechanisms, thanks to which the entire volume of food that enters the stomach is digested and gradually moves further. The work of the stomach at this moment is performed thanks to peristaltic waves, topical contractions of the fundus and body of the stomach, and systolic contractions of the pyloric region.
During movement, food components continue to dissolve, digest and be processed by gastric juice. The result of this functional work is the complete dissolution of food components.
Suction
This is one of the most important tasks: nutrients necessary for humans are extracted from food products and they must enter the bloodstream so that, thanks to their delivery to target organs, the corresponding metabolic processes occur:
- protein;
- fatty;
- carbohydrate;
- absorption of vitamins;
- production of vital enzymes and hormones;
- tissue growth.
Absorption of components occurs at different stages of the digestive process, but the largest part of them enters the bloodstream from the stomach.
Secretory
The production of gastric juice is the secretory activity of the gastric glands: fundic, cardiac and pyloric. Each of them enters into productive activity gradually, as food progresses, but the insufficiency or absence of any group due to illness or surgery leads to defective digestion. This condition requires medication and restorative correction.
Composition and properties of gastric juice
Gastric juice is a multicomponent, colorless liquid, the transparent, dense part of which consists of chlorides, phosphates, sulfates, magnesium and potassium, contained in the form of cations. The main inorganic component is hydrochloric acid. It is thanks to it that food is digested and necessary substances are extracted from it.
The gastric juice also contains enzymes: proteases and lipases. The former are necessary for the breakdown of protein into amino acids. This is how protein metabolism begins.
Lipases are necessary to dissolve fats into glycerol and fatty acids. Other enzymes not involved in proteolysis are represented by lysozyme and urease. Lysozyme dissolves the bacterial wall, thereby promoting the bactericidal effect of gastric juice. Urease breaks down urea into carbon dioxide and ammonia, which is extremely important for carbohydrate metabolism.
The gastric juice contains another important fraction - peptidoglycans, glycoproteins. These substances protect the gastric mucosa from self-dissolution by their own enzymes.
Regulation and phases of gastric secretion
The process of secretion of gastric juice is regulated by conditioned reflex mechanisms and unconditioned reflex mechanisms. With excessive stimulation of the unconditioned reflex arcs, there is a high risk of developing hyperacid gastritis, so this situation can be corrected by surgical dissection of the vagal nerve, which transmits excess excitation. Malignant tumors in the central nervous system can also be the cause.
It is customary to distinguish three phases of gastric secretory activity:
- cerebral or complex reflex;
- gastric;
- intestinal
From the names it is clear that the beginning of the entire chain occurs at the level of the brain with remote irritation by the sight, smell, conversations about food and the entry of its first components into the oral cavity. The gastric phase begins when a bolus of food is swallowed. This can be either stimulating or inhibitory, depending on the nature of the food.
The intestinal phase begins when chyme falls into the duodenal lumen. Insufficient digestion of food at the stomach stage can lead to diarrhea or constipation.
Non-digestive functions of the stomach
The process of nutrition is a pleasure, providing vital human needs, but also a component of some of the most important general reactions of the body. The stomach not only performs the functions of digesting or absorbing nutrients, but also the following important tasks:
- protective;
- excretory;
- hematopoietic;
- support of water-salt metabolism.
They are necessary for the whole body.
Useful video
How the stomach functions is described in this video.
Protective
Many microorganisms enter the stomach with food, saliva, and water. Thanks to the bactericidal effect of gastric juice, the vast majority of bacteria die and do not cause infectious processes.
Excretory or excretory
A number of heavy metals and harmful substances of medicinal or narcotic properties are released from the internal environment with the help of gastric juice. It is this ability that is used in the treatment of emergency conditions during gastric lavage in case of poisoning with substances of this nature.
Hematopoietic
The main task of the mucopeptide contained in gastric juice is to help absorb the vitamin cyanocobalamin into the blood. When a part of the stomach is resected or there is insufficiency of this component, B12 deficiency anemia develops.
Homeostatic or support of water-salt metabolism
The participation of juice components in the humoral regulation of processes, thereby maintaining the stability of the internal environment of the body.
Functional disorders
A detailed examination of all the functions that the stomach performs allows us to talk about its most important role in maintaining the stability and health of the human body. Failure of any of the above tasks leads to diseases not only of the gastrointestinal nature, but also to anemia - anemia, the development of bacterial infections, and insufficient supply of nutrients and building substances.
Hormones are produced in insufficient quantities, therefore, the endocrine system suffers, that is, the lack of protein and carbohydrates leads to a decrease in the intensity of cellular metabolism and respiration, which affects all tissues: from muscle to mucous membranes.
(1 ratings, on average: 5,00 out of 5) 
Loading...
