Motor function of the digestive tract. Functions of the stomach Motor function of the stomach
Modern research methods - x-ray, cinematographic, and visual observations - have made it possible to establish three types of motor phenomena in the stomach: peristaltic, systolic and tonic. The motor function of the stomach is ensured by the smooth musculature. This function helps to mix, crush and move the stomach contents into the duodenum.
Peristaltic movements are carried out by contraction of the circular muscles of the stomach. The contraction wave begins in the cardiac region and spreads to the pyloric sphincter. Peristaltic waves occur in humans with a frequency of 3 times every 1 minute.
Systolic contractions are associated with contraction of the muscles of the antrum of the pylorus of the stomach. These movements ensure the passage of a significant part of the stomach contents into the duodenum.
Tonic contractions are non-peristaltic movements of the stomach caused by changes in muscle tone. An increase in the tone of the stomach muscles leads to a decrease in the cavity in this section or throughout the stomach and to an increase in pressure in it. Tonic contractions also help move stomach contents. With a decrease in muscle tone, especially the fundus of the stomach, the volume of the organ increases, which creates conditions for a greater flow of food into this section of the digestive tube.
When the stomach is empty, periodic contractions occur (hungry motility), which are replaced by a state (period) of rest. This type of contraction of the stomach muscles is associated with a feeling of hunger. In humans, the duration of periods of gastric activity is 20-50 minutes, periods of rest last 45-90 minutes or more. Periodic contractions of the stomach stop when eating and digestion begin. In addition to these types of contractions, there is antiperistalsis in the stomach, which is observed during the act of vomiting.
Regulation of gastric motor function carried out due to neurohumoral mechanisms. The vagus nerves excite the motor activity of the stomach, while the sympathetic nerves inhibit it in most cases. It has been proven that the phrenic nerves containing parasympathetic fibers play a certain role in the regulation of the motor function of the stomach. Humoral factors influence gastric motility. Contraction of the smooth muscles of the stomach is stimulated by insulin, gastrin, histamine, and potassium ions; they are inhibited by enterogastron, cholecystokinin-pancreozymin, adrenaline, and norepinephrine. Mechanical irritation of the intestines with a wide variety of nutrients leads to reflex inhibition of the motor activity of the stomach (enterogastric reflex). This reflex is most pronounced when fat and hydrochloric acid enter the duodenum. A powerful stimulator of the motor activity of the stomach is the act of eating and irritation of the stomach receptors with food.
The act of vomiting. Vomiting is a complex coordinated reflex act, which under normal conditions performs a protective function, as a result of which substances harmful to it are removed from the body.
Vomiting occurs when the receptors in the pharynx, root of the tongue, and stomach are irritated by poor quality food or its excessive quantity. In addition, vomiting can be observed when vestibular receptors are irritated (while traveling on a train, plane, car, ship), olfactory, visual receptors (with the smell and sight of poor-quality products), and receptors of internal organs (for example, with inflammatory diseases of the abdominal organs) . From the receptors, nerve impulses enter the corresponding center in the medulla oblongata and increase its activity. Chemical substances in the blood (waste products of bacteria, toxins, some drugs, for example, apomorphine, etc.) can also have a stimulating effect on the center.
The act of vomiting begins with contractions of the muscles of the small intestine, while the intestinal contents move through the open pyloric sphincter into the stomach. Contraction of the smooth muscles of the stomach (antiperistalsis) delivers the contents of the stomach to its cardiac region. The cardiac sphincter opens and the contents of the stomach flow into the esophagus, into the oral cavity and out. During the act of vomiting, there is a strong contraction of the abdominal muscles and diaphragm, which contributes to the reflex reaction.
Motor function of the gastrointestinal tract
The motor function of the gastrointestinal tract is based on the contractile activity of smooth muscle cells; they comprise three layers:
External longitudinal
Medium circular
Internal longitudinal
The main feature of the smooth muscle cells of the gastrointestinal tract is their ability to automate. Automaticity is the basis of all types of motor activity (motor) of the gastrointestinal tract, the main types of motor activity of the gastrointestinal tract:
Tonic waves
Peristalsis
Antiperistalsis
Systolic contractions
Rhythmic segmentation
Pendulum contractions
The act of chewing leads to a reflex increase in the tone of the smooth muscles of the stomach, however, during swallowing, receptive relaxation occurs - reflex relaxation of the smooth muscles of the stomach (the most favorable conditions for filling the stomach with food).
After filling the stomach, due to the great plasticity of its muscles and increased tone when they stretch, food is tightly enveloped by the gastric walls. In a stomach filled with food, three types of motor activity are observed:
Further grinding of food
Mixing
Consolidation of food that comes from the mouth
Tonic waves– these are high-amplitude, long-lasting and slowly spreading contractions, which are caused by the redistribution of muscle tone. The main tasks of tonic waves are:
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 direction; this is due to the narrowing of the gastric lumen proximal to the chyme and the expansion of the gastric cavity distal to it. The immediate cause of half-digested food is the proximodistal pressure gradient. Peristaltic waves arise near the cardiac part of the stomach, located at the lower end of the esophagus, they spread towards the pyloric (antral) part adjacent to the duodenum. The speed of wave propagation increases from one centimeter per second in the cardiac region to 3.4 in the pyloric region. Due to this, the pyloric region contracts as a single functional formation, that is, a systolic contraction is observed. Due to systolic contraction of the antrum and simultaneous relaxation of the smooth muscle of the pyloric sphincter, a proximodistal pressure gradient occurs. A portion of acidic gastric chyme enters the duodenum along the gradient of this pressure. In the duodenal bulb in the initial section, the acidic gastric chyme irritates the chemo and mechanoreceptors, which causes an inhibitory enterogastric reflex. The motor evacuation function of the stomach is inhibited and the smooth muscles of the pyloric sphincter are contracted, which ensures discrete (intermittent) evacuation of acidic gastric chyme and prevents its return.
Systolic contractions
Mechanisms of regulation of motor function stomach are divided into enteral (local) and extraenteric. Local enteral ones can be neurogenic and humoral; they are provided by the reflex activity of the enteric metasympathetic nervous system and gastrointestinal hormones.
Extraenteric mechanisms are carried out using peripheral and central reflexes, the reflex effect occurs when the receptors of the mouth, pharynx, esophagus, as well as interoreceptors of the gastrointestinal tract are irritated; signals are transmitted to the smooth muscles of the stomach using the efferent fibers of the vagus and sympathetic splanchnic nerves. Excitation of the nerve fibers of the vagus nerve 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. The parasympathetic system stimulates the motor function of the stomach. Stimulates the muscles that line the stomach wall, relaxes the pyloric sphincter muscles. The difference is due to the receptors. Efferent control neurons are different.
Excitation of sympathetic nerve fibers has an inhibitory effect, the frequency and strength of gastric contractions decreases, the speed of propagation of peristaltic waves decreases, at the same time, contractions of the pyloric sphincter have a sympathetic effect.
The higher parts of the central nervous system (hypothalamus, limbic system, cerebral cortex) are involved in the regulation of the motor function of the stomach; in general, the central nervous system has an inhibitory effect, therefore, with complete denervation, gastric motility increases significantly. The experience of fear and pain, increased psycho-emotional stress causes inhibition of motor skills, but strong and prolonged negative emotions lead to its intensification.
Further mechanical processing - mixing of chyme with alkaline mechanical enzymes and its movement in the distal direction is ensured by motor activity small intestine .
The main types of motility of the small intestine:
Tonic waves - in the small intestine are local in nature
Peristalsis
Rhythmic segmentation is a variable contraction and relaxation of circular smooth muscle fibers of the intestine, which occurs simultaneously in several neighboring areas.
Pendulum-like contractions are alternating relaxation and contraction of the longitudinal smooth muscle fibers of the intestine, which occurs simultaneously in several neighboring areas.
Main functions:
Mixing
Grinding
Consolidation of the intestinal chyme, which is caused by its reciprocating movements
In the regulation of small intestinal motility, local internal mechanisms predominate:
Myogenic mechanisms are associated with the ability of smooth muscle cells of the small intestine to contract spontaneously or respond to contraction when stretched; it is supplemented by the reflex activity of the internal metasympathetic nervous system and the influence of gastrointestinal hormones.
The extraenteric reflex effect on the motor activity of the small intestine is weakly expressed. Excitation of the parasympathetic fibers of the vagus nerve enhances the motility of the small intestine, while 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.
Neurogenic
Humoral
From the small intestine, portions of alkaline intestinal chyme enter through the iliocecal sphincter into the colon , the peristaltic wave of the small intestine causes a reflex opening of the ilicecal 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 iliocecal sphincter, which means it inhibits further flow from the small intestine.
The main types of contraction of the large intestine:
Tonic contractions
Peristalsis
Rhythmic segmentation
Pendulum contractions
Antiperistalsis is a wave-like contraction of circular smooth muscle fibers of the intestine distally, and longitudinal ones proximal to the contents.
Main function– creation of a distoproximal gradient, which ensures the advancement of contents by 15-20 cm into the proximal parts of the large intestine, for additional processing and absorption of water.
The leading role in the regulation of colon motility belongs to local regulatory mechanisms:
Myogenic
Neurogenic
Humoral
Irritation of the efferent fibers of the parasympathetic vagus nerve leads to activation of motor activity of the small intestine. Sympathetic nervous system inhibits the motor activity of the colon.
In the activity of the digestive system, there are regular periodic changes in motor and secretory activity not related to food intake. Periodic extra-digestive increase in the activity of the digestive organs is called hungry intermittent activity , in the process of periodic fasting activity, a period of work and a period of rest are distinguished. In humans, cycles of periodic activity consist of 20 minute periods of increased activity and 750 minutes of relative rest.
Physiological significance of intermittent fasting activity:
Satisfying the plastic and energy needs of the body is the supply of proteins from digestive juice.
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.
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 oral cavity, then it irritates the receptors of the mucous membrane, this causes contraction of the digastric muscle, which promotes lowering of 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 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, chemical composition and the 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 a 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.
Under motor function understand the totality of all types of movements of the walls of the stomach, which ensure mixing of food with gastric juice, movement of contents towards the intestines and evacuation of it in portions into the duodenum.
It is ensured by the coordinated activity of smooth muscles (the outer layer is longitudinal, the inner layer is circular, in the area of the cardium - oblique) of the walls and sphincters and is regulated by local and central neurohumoral mechanisms.
Outside the period of digestion, on an empty stomach, the smooth muscles of the stomach are in a certain tone. If the fast is long, then every 60-90 minutes periodic contractions of the stomach occur (“hunger periods”), which last 20-40 minutes and are replaced by a state of rest.
Types of stomach contractions:
1. Peristaltic- 3-4 contractions per 1 minute, lasting 5-20 s; spread in a ring-like manner, intensifying towards the antrum.
2. Tonic- associated with peristaltic, longer and stronger 2-4 per 1 min, 15-30 s.
Both types maintain pressure in the stomach cavity and promote mixing of food with gastric juice in the layers adjacent to the wall. They are relatively weak during the first hour after feeding; then they intensify, especially in the pyloric part, pushing the juice-soaked stomach contents to the exit into the intestines.
3. Systolic- contraction of the antrum of the stomach, up to 60 s. They ensure the passage of part of the contents into the duodenum.
4. Antiperistaltic(vomiting, regurgitation in ruminants).
Lecture 22-23.
Digestion in the intestines.
1. The pancreas, its role in digestion. Composition and properties of pancreatic juice.
2. Liver, its functions. Composition and role of bile in intestinal digestion. Bile formation and bile excretion.
3. Features of digestion in the small intestine. Intestinal juice, its composition and properties.
4. Methods for studying the secretion of intestinal juice.
5. Transition of food masses from the small intestine to the large intestine.
6. Formation of feces in the large intestine. The act of defecation and its regulation.
7. Motor function of the intestines.
8. Regulation of motor function of the gastrointestinal tract. Methods for studying the functions of the gastrointestinal tract.
9. Membrane (parietal) digestion.
10. Absorption function of the intestine.
11. Features of digestion in birds
n 1. The pancreas, its role in digestion. Composition and properties of pancreatic juice.
n Feed masses entering the duodenum are exposed to pancreatic juice, bile and intestinal juice.
n Pancreas - the main digestive gland. The duct opens into the duodenum.
n Functions:
n 1. Incretory (endocrine) – formation of hormones: insulin, glucagon.
n 2. Excretory (exocrine, secretory) – digestive – formation of enzymes.
n Pancreatic juice - l/day: horse – 7.5-8.5; Cattle – 7-7.5; MRS – 0.5-0.6; pig – 7-8; rabbit – 0.04-0.05; dog – 0.2-0.3.
n In carnivores (dogs, cats), iron is secreted periodically after eating food and the contents enter the intestines; in farm animals it is secreted continuously, increasing during feeding.
n pH 7.2-8.5 – slightly alkaline, ρ = 1.008-1.010, water – 90%. Inorganic substances - Na, Ca, K cations, bicarbonate and chloride anions, organic substances - enzymes.
n Enzymes in the small intestine:
n Intestinal juice:
n 1. Trypsinogen(inactive) + enterokinase (intestinal enzyme) → trypsin (active) + proteins, polypeptides → polypeptides and amino acids.
n 2. Chemotrypsinogen(inactive) + enterokinase (intestinal enzyme) → chemotrypsin (active) + proteins, polypeptides → polypeptides and amino acids.
n Then the process becomes autocatalytic, i.e. trypsin itself becomes an activator of trypsinogen and chemotrypsinogen.
n 3. Carboxypeptidase+ peptides → amino acids.
n 4. Elastase+ elastin and collagen → amino acids.
n 5. Protominase+ protamines → amino acids.
n 6. α-amylase+ starch, glycogen, dextrins → maltose.
n 7. Lipase(activated by bile) + lipids → glycerol, monoglycerides and fatty acids.
n 8. Phospholipase+ phospholipids → glycerol, fatty acids, phosphoric acid, choline.
n Pancreatic juice:
n 9. Nucleases (ribonuclease, deoxyribonuclease)+ nucleic acids (RNA, DNA) → mononucleotides and phosphoric acid.
n 10. Peptidase+ oligopeptides → amino acids.
n 11. Maltase(disaccharidase) + maltose → glucose.
n 12. Invertase or sucrase(disaccharidase) + sucrose → glucose and fructose.
n 13. Lactase(disaccharidase) + lactose (milk sugar) → glucose and galactose.
n 14. Alkaline phosphatase+ phosphorus esters → dephosphorylated compounds.
n Phases of pancreatic juice secretion (3-4 hours):
n 1. Complex reflex(short-term) – when food irritates the receptors of the oral cavity;
n 2. Gastric– when irritating stomach receptors and releasing gastrin;
n 3. Intestinal– main, regulated humorally by hormones of the digestive tract - gastrin, secretin (stimulates the secretion of the liquid part and bicarbonates), cholecystokinin (pancreozymin) (enzymes), as well as insulin and prostaglandins.
n Glucagon, norepinephrine, and ADH inhibit the secretion of pancreatic juice.
n 2. Liver, its functions. Composition and role of bile in intestinal digestion. Bile formation and bile excretion.
n Liver functions :
n 1. Formation of bile;
n 2. Participation in metabolism;
n 3. Glycogen synthesis, its depot;
n 4. Detoxification, breakdown of alcohol, medicinal and other substances.
n 5. Blood depot, in the embryonic period – hematopoietic organ.
n Horses, deer, camels, roe deer, rats, pigeons do not have a gallbladder; its role is played by the bile cistern - an expansion of the common hepatic duct.
n Bile is produced in the lysosomes of liver hepatocytes and is drained through the intrahepatic bile ducts (bile capillaries, bile and interlobular ducts), and then through the common hepatic and cystic ducts into the gallbladder.
n The common bile duct enters the duodenum, usually together with or next to the pancreatic duct (except for pigs and cattle), from the gallbladder or directly from the liver. Extrahepatic sphincters - at the base of the cystic, common hepatic and common bile ducts - distribute bile into the bladder and intestine.
n Bile is secreted continuously by the liver and released into the intestines during digestion in carnivores or continuously in farm animals (ruminants, horses, pigs, rabbits).
n Amount of bile l/day: cattle – 7-9, horse – 5-6, small cattle – 0.8-1, pig – 2.5-3, rabbits – 0.02-0.03, dogs – 0, 2-0.3.
n Bile happens:
n 1. Bubble- (due to absorption in the bladder and secretion of mucin) darker, thicker, viscous. P = 1.030-1.045, water - 85%, pH - 5.5-6.5 (dark green in ruminants, red-yellow in carnivores).
n 2. Hepatic:ρ = 1.010-1.015; water – 97.5; pH -7.4-8 (light green in ruminants, light yellow in carnivores).
n Composition of bile:
n 1. Bile acids (1%) – cholic, deoxycholic, chenodeoxycholic, glycocholic, taurocholic.
n 2. Mineral salts (0.8%): Na, K, Ca, carbonic, phosphoric and other acids.
n 3. Bile pigments (0.2%): bilirubin (formed from hemoglobin during the destruction of red blood cells in the liver), biliverdin (formed during the oxidation of bilirubin).
n 4. Mucin (0.3%).
n 5. Fatty acids (0.14%).
n 6. Cholesterol, lecithin (0.08%).
n 7. Phosphotides.
n 8. Saponified and free fats (0.4-0.5%).
n 9. Protein breakdown products - urea, uric acid, purine bases.
n Bile salts (biologically more important component) in the intestine combine with fatty acids and, with the participation of cholesterol, form micelles in which fats are transported into epithelial cells. Once absorbed, the salts are transferred to the liver and again excreted in the bile. This cycle is repeated several times a day.
n Functions of bile:
n 1. Enhances the action of enzymes (intestinal lipase);
n 2. Emulsifies fats;
n 3. Bile acids are involved in the absorption of fatty acids, their salts, fat-soluble vitamins: A, D, E, K;
n 4. Strengthens intestinal motility;
n 5. Strengthens the secretion of pancreatic juice;
n 6. Reduces the surface tension of water-fat solutions, facilitating the action of lipases;
n 7. Bactericidal and deodorizing effect.
n 8. Neutralizes acidic contents, stops the effect of pepsin.
n Bile formation and bile secretion are under neurohumoral control.
n They are stimulated by: reflex influences from the stomach and other internal organs through the vagus and phrenic nerves, as well as hormones: gastrin, secretin, cholecystokinin and bile acids in the blood (depending on the fat content of food).
n Contraction of the gallbladder and relaxation of the sphincters is influenced by the vagus nerve, with irritation of the receptors of the mouth, stomach, and duodenum (complex reflex phase of digestive secretion). Sympathetic nerves have the opposite effect.
n 3. Features of digestion in the small intestine. Intestinal juice, its composition and properties.
n Small intestine: duodenum, jejunum and ileum.
n The food mass comes from the stomach into the duodenum in portions.
n The contents of the stomach entering the duodenum, under the influence of pancreatic juice, intestinal juice and bile, takes the form of a liquid homogeneous mass called chyme .
n It can be studied in animal experiments with an external anastomosis (bridge) placed on the jejunum.
n Conditions for the opening of the pyloric sphincter and the passage of contents from the stomach to the intestines:
n 1. In the pyloric part of the stomach there is homogeneous content and an acidic reaction of the environment.
n 2. In the duodenum there is a lack of contents and an alkaline reaction of the environment.
The opposite conditions are necessary for the sphincter to close.
Length of the small intestine: cattle - 40-49 m, small cattle - 24-26 m, horse, pig - 20 m, human - 7-8 m.
n Intestinal juice - stands out continuously, colorless, slightly cloudy, pH in the duodenum is 8.5-9.0; in the jejunum and ileum – 7.5-8.5.
n Inorganic substances – electrolytes: Cl, Na, K, Ca.
n Organic substances - enzymes, mucus, epithelial cells, cholesterol.
n Regulation of juice secretion in the intestines:
n Nervous regulation:
n - parasympathetic NS – stimulates,
n - sympathetic – depresses.
n Humoral regulation:
n HCl, coming from the stomach into the duodenum, irritates the mucous membrane, which produces:
n - prosecretin (inactive form of digestive hormone) + HCl → secretin, which is absorbed into the blood, stimulates the secretion of pancreatic juice, inhibits the release of HCl.
n - pancreozymin – enhances pancreatic secretion;
n - cholecystokinin - stimulates contraction of the gallbladder muscles and relaxation of the sphincter.
n Gastrin produced in the stomach enters the blood and stimulates the pancreas.
n The intestinal mucosa has projections - villi and crypts located between them (Lieberkühn's glands).
n 1. goblet enterocytes - producing mucus,
n 2. enterocytes with basophilic granules - enzymes,
n 3. enterochromaffinocytes - endocrine cells;
n Villi have two types of cells:
n 1. epithelial cells with a striated border - absorption function,
n 2. goblet enterocytes.
n In the submucosal layer of the duodenum there are Brunner's glands, which secrete a thick, viscous secretion that protects the mucous membrane from the effects of HCl gastric juice.
n 4. Methods for studying the secretion of intestinal juice.
n 1. Thiry method – surgical isolation of a section of the intestine, one end of which is sutured tightly, and the other is sewn into the skin wound. The ends of the cut intestine are stitched to restore integrity.
n 2. Thiri-Vell method – removal of both ends of an isolated section of intestine into a skin wound.
n 3. Thiry-Pavlov method – the intestinal loop is isolated as a result of disconnection of the mucous membrane between the main intestine and its separated section, while the seromuscular connection is preserved, i.e. reflects nervous and humoral regulation.
n 5. Transition of food masses from the small intestine to the large intestine.
n The large intestine consists of the cecum, colon and rectum.
n Makes up 10-15% of the total volume of the gastrointestinal tract in carnivores and ruminants, 40-60% in horses and rabbits, an intermediate position in pigs.
n In herbivores with a single-chamber stomach, the digestion of poorly soluble plant components of food occurs here (similar to the proventriculus of ruminants). In carnivores, the role is small, because Most of the products of nutrient hydrolysis are absorbed in the small intestine. pH 6.9-7.2.
n From the small intestine, the undigested food mass enters the cecum through the ileocecal sphincter (in horses, rabbits) or valve (in ruminants, pigs and dogs), which periodically opens and closes, allowing the food mass to pass in portions. Next - into the colon, where feces are formed. When the cecum is full, the ileocecal sphincter does not open until the food masses pass into the colon. The mucous membrane of the large intestine does not have villi, contains many folds and crypts, is poor in secretory cells, and secretes mainly mucus from goblet cells, which is of great importance in the formation of feces. Partial digestion occurs due to enzymes supplied with chyme from the small intestine.
n A large amount of microflora accumulates in the large intestine: bacteria, ciliates, etc., which contributes to rotting and fermentation. As a result of the activity of microflora, substances accumulate in the large intestine: ammonia, indole, skatole, cresol, phenol, which are neutralized in the liver. As a result of fermentation, gases accumulate - hydrogen, hydrogen sulfide, carbon dioxide, methane, etc., volatile fatty acids - acetic, butyric, etc. Normally, there is a certain balance of different groups of microorganisms. The products of rotting and fermentation suppress the activity of bacteria.
n The large intestine is where fiber is digested. Cellulolytic bacteria secrete the enzyme cellulase, which breaks down cellulose, producing cellobiose, which is broken down by the enzyme cellobiase into glucose.
n In ruminants, 30% of fiber is broken down in the colon, in omnivores - 10-15%, in carnivores - not.
n 6. Formation of feces in the large intestine. The act of defecation and its regulation.
n Feces are formed in the lower part of the colon due to the compaction of food debris and the removal of water.
n Feces - a heterogeneous dense mass consisting of food debris, waste products of the intestine, dead epithelial cells, mucus, bile acids, enzymes, etc.
n Fecal masses accumulate in the lower part of the colon and pass into the rectum through the internal sphincter, consisting of smooth muscles. External sphincter made of striated muscles. The sphincters are in constant tone under the influence of the central nervous system. From the baroreceptors of the rectum (at a pressure of 50 mm Hg), the impulse enters the lumbar region the spinal cord, and from there to the sphincters - they relax. When straining, the abdominal muscles and diaphragm are also involved.
n Defecation - a complex reflex act of removing fecal matter from the intestine. Consists of two phases:
n 1. Afferent – formation of urge;
n 2. Efferent – release from feces.
n 7. Motor function of the intestines.
n The smooth muscles of the intestine are represented by longitudinal and circular fibers.
n Types of intestinal contractions:
n 1. Peristaltic (worm-shaped) - above the food coma, the circular muscles contract, and below, the longitudinal muscles contract and the intestines expand in this place. 4-5 contractions/min, speed of chyme advancement - 1-2 cm/sec Function: advancement of food masses in the caudal direction.
n 2. Rhythmic segmentation – the circular muscles form interceptions (6-8 cm from each other), between which the longitudinal muscles contract rhythmically. The frequency of contractions is 20-30 per minute in the small intestine, 8-10 in the large intestine. Function: grinding and mixing the chyme.
n 3. Pendulum-shaped – occur during synchronous contractions of the circular and longitudinal muscles in a certain area of the intestine, as a result of which the isolated area either shortens, simultaneously expanding, or lengthens and narrows. Function – mixing, homogenization of chyme, promotes parietal digestion.
n 4. Tonic - (often in pathology) against the background of general tone, the intestinal lumen narrows at a considerable distance, spastic, long-lasting - 1 contraction lasts 1 minute or more.
n 5. Antiperistaltic - promote food masses in the oral direction. They are observed in the upper part of the small intestine - the duodenum (throwing bile into the stomach) and in the large intestine - in the cecum.
n 8. Regulation of motor function of the gastrointestinal tract.
n Nervous regulation:
n 1. Intramural (intrawall) innervation - Auerbach and Meissner plexuses - provides local reflexes;
n 2. Extramural innervation –
n - sympathetic NS (celiac nerve) – inhibitory effect (relaxation of smooth muscles);
n - parasympathetic NS (vagus nerve) – excites, enhances.
n Humoral regulation : hormones of the digestive tract and physiologically active substances.
n - stimulate – oxytocin, gastrin, insulin, motilin, serotonin, histamine, prostaglandins, acetylcholine;
n - inhibit – secretin, cholecystokinin (pancreozymin), adrenaline, norepinephrine.
n Methods for studying the functions of the gastrointestinal tract.
n 1. Ballonographic
n 2. X-ray
n 3. Electrographic
n 4. Radiotelemetric
n 5. Ultrasound – ultrasound examination
n 9. Membrane (parietal) digestion
n There are 2 types of digestion:
n 1. Cavity – in the intestinal cavity, the breakdown of nutrients by enzymes of pancreatic and intestinal juice, with the participation of bile. Large molecular compounds are hydrolyzed, mainly oligomers are formed.
n 2. Parietal (A.M. Ugolev) – in the peri-membrane structure (glycocalyx) microvilli intestines (mainly in the jejunum). The products (mainly monomers) formed during hydrolysis are transported by transport systems of the same membranes into the intestinal cell and then into the blood.
n Thus, digestion is a three-link process: cavity digestion - membrane digestion - absorption.
n Features of parietal digestion
n 1. The breakdown of nutrients occurs due to enzymes adsorbed from the chyme and enzymes structurally associated with the membrane.
n 2. Enzymes act on the entire food mass passing through this section of the intestine.
n 3. The useful life of enzymes fixed on the surface of intestinal cells is much longer than in the intestinal cavity.
n 4. The formation of absorption products is determined not by cavity, but by parietal digestion.
n 5. Bactericidal effect of the bordered epithelium: bacteria cannot penetrate through it, because have a large mass.
n 6. Large suction area.
n 10. Absorption function of the intestine.
n Absorption is associated with parietal digestion. Max absorption in the small intestine, in ruminants in the rumen, book.
n By suction - an active physiological process of unilateral penetration of various substances through layers of cells into the blood or lymph.
n Absorption occurs from the surface of the skin, mucous membranes, stomach, lung alveoli, etc. The intestinal one is of greatest importance, because there is a special suction apparatus - macrovilli , as a result, nutrients enter the body. They increase the suction area by 8-10 times.
n When smooth muscles contract, lymphatic vessels and capillaries contract and squeeze lymph and blood into the main vessels. When the muscles relax, blood and lymph do not enter the villus cavity due to the presence of special valves. But the pressure in the villi drops, so nutrients from the intestines come here. The villi are finger-shaped, 0.2-1 mm long, the number is 20-40 per 1 square meter. mm.
n Villous epithelial cells have a striated border consisting of microvilli 2 x 0.10-0.15 microns, number 80-120 per 1 square. mm villus area. Microvilli increase the suction surface another 100 times.
n 11. Features of digestion in birds.
n Morphological:
n a) absence of teeth, presence of a beak, simple structure of the nasopharynx, absence of the epiglottis; b) the presence of a goiter or a corresponding dilation of the esophagus;
n c) the presence of a two-chamber stomach with glandular and muscular sections;
n d) relatively short small intestine;
n e) well-developed liver and pancreas, having 2-3 ducts each;
n e) the presence of two cecums and a cloaca into which the digestive, reproductive and urinary tracts open.
n Physiological:
n 1. When swallowing, the larynx rises forward and upward, and the entrance to it is closed by the movable base of the tongue.
n 2. Feed gets into goiter(in geese and ducks, instead of a goiter, there is an ampulla-shaped expansion of the esophagus and a sphincter at the outlet). Its glands secrete mucus, which does not contain enzymes, digestion is due to enzymes of food and microorganisms (bacteria, fungi) and a little due to amylolytic enzymes of the salivary glands, which are poorly developed in birds. Proteolysis, lipolysis and especially amylolysis (15-20%) of the feed are carried out; fiber is practically not broken down. The food is in the crop for 1-18 hours. Motility of the crop begins 35-40 minutes after feeding - a periodic series of contractions (10-12 in 1 hour) lasting 20-30 seconds each, with a force of 8-12 mm Hg. Art., regulated by the vagus nerve.
n 3. Glandular stomach - ampoule-shaped expansion of the digestive tube with thickened walls. The glands produce gastric juice and hydrochloric acid. The total acidity of the juice ranges from 0.2 to 0.5%. All proteolytic enzymes are varieties of pepsin. The stomach of birds is never empty, juice secretion is continuous. There are all three phases of gastric juice secretion: complex reflex, gastric and intestinal.
n 4. Muscle stomach- a disc-shaped organ connected by a short isthmus to the glandular stomach. The basis is made up of two pairs of powerful smooth muscles - the main and intermediate ones. The cavity has a bag-like, slit-like shape, the entrance to and exit from the stomach are close together. The inside of the stomach is covered with hard cuticle, formed by the hardened secretion of the glands located underneath. The cuticle is constantly renewed. Here the feed is mechanically processed (ground) and the proteins are hydrolyzed (35-50% 2-4 hours before polypeptides) under the influence of proteinases from the glandular stomach juice, as well as part of the carbohydrates and lipids (10-15%) due to the enzymes of the pancreatic juice thrown from the duodenum.
n 5. The motor function of the stomach consists of regular movements of the glandular stomach and synchronous rotational-tonic contractions of the muscular stomach, followed by movements of the duodenum. The frequency of contractions is 2-4 per 1 minute after feeding and 1-2 per 5 minutes at rest. In this case, the pressure in the cavity of the muscular stomach increases to 100-160 mm Hg. Art. in chickens and up to 250 mm Hg. Art. at the geese. This ensures crushing, grinding (using gravel, glass, etc.) and compaction of the contents. Regulation - vagus nerve.
n 6. The duration of stay of chyme in the small intestine is 1-2 hours.
n 7. Pancreatic juice and bile are secreted continuously at a rate of 25 ml per 1 kg of body weight per hour (i.e. more than other animals), pH 7.5-8.1 and 7.3-8.0, respectively. Lactase was not detected in pancreatic juice.
n 8. Features of intestinal digestion in chickens: absence of Brunner's glands (and duodenal juice); poor development of lymphatic cisterns in the villi and the system of milky lymphatic ducts; intensive processes of parietal digestion. The amount of intestinal juice is no more than 10 ml/hour per 1 kg of weight, pH 7.0-7.2.
n 9. Unlike animals, birds have an acidic or neutral reaction in almost all parts of the gastrointestinal tract: the pH of the crop is 4-6, in the glandular stomach - 1.0-2.0, in gizzard- 2.5-3.5, in the duodenum - 6.0-7.0, in the jejunum - 6.5-7.1, in the ileum and cecum - 6.8-7.5.
n 10. The blind processes in birds perform the functions of breaking down fiber with the participation of microflora (6-9%), synthesis of B vitamins, absorption of water, mineral elements and fermentation products, the role of lymphoid formations.
n 11. Evacuation of feed from the digestive tract of chickens 16-18 hours
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