Which animal has salivary glands? What type of muscle tissue do the walls of the stomach consist of? What are its features?
Salivary glands first appear in amphibians.
The walls of the stomach are formed by smooth muscle tissue, which contains thin filaments capable of slow contraction.
1. Name the functions of saliva.
Saliva wets food, which facilitates its further passage, in addition, saliva contains digestive enzymes and substances that kill microbes.
2. Why does starch decompose under the action of saliva, forming sugar?
Enzymes that are contained in saliva act on it.
3. What functions do the tongue, epiglottis and palatine uvula perform during swallowing?
The tongue performs the function of mixing food, determining taste; the epiglottis does not allow food to enter the trachea when swallowed, blocking it with itself; the uvula does the same, but blocks the access of food to the nasopharynx.
4. Try to swallow several times in a row. Why is it possible to do this no more than two or four times?
The saliva we swallow is gastric juice. With swallowing movements made in a row, saliva is not deposited in the oral cavity, so there is nothing to swallow.
5. Explain the results of the experiment with a starched bandage on which the letters were written with saliva. Why did a white letter appear on a blue background after treatment with iodine water?
Since starch, under the action of enzymes that are contained in saliva, has turned into glucose.
6. What layers does the wall of the stomach consist of and what function do they perform?
The cells of the inner layer of the walls of the stomach secrete gastric juice, which includes mucus, hydrochloric acid and enzymes that ensure the digestion of food. Hydrochloric acid kills harmful microorganisms, promotes the process of digestion. Under the action of the enzyme of gastric juice (pepsin), protein molecules break down into simpler compounds. The inner wall of the stomach has numerous folds that increase the surface of the mucosa that secretes gastric juice.
The middle layer of the stomach wall is formed by smooth muscle tissue. Contracting and relaxing, the muscles mix its contents with gastric juice. This contributes to better digestion of food.
The outer layer consists of the peritoneum - outgrowths of the inner wall of the abdominal cavity, which cover the stomach and fix its position.
In the stomach, food is from 3 to 6 hours. It turns into a semi-liquid slurry, which gradually, in portions, enters the intestines.
7. Why, along with digestive enzymes, the glands of the stomach secrete hydrochloric acid?
Since pepsin acts only in an acidic environment.
8. What experience can prove that gastric juice digests proteins only in an acidic environment?
Gastric juice itself has an acidic pH. If you bring the pH to neutral or alkaline, that is, more than 6, protein digestion will already stop.
Can you complete this task: "List the human digestive glands"? If you doubt the exact answer, then our article is exactly for you.
Gland classification
Glands are special organs that secrete enzymes. They are which accelerate the process of chemical reactions, but are not part of its products. They are also called secrets.
There are glands of internal, external and mixed secretion. The first release secrets into the blood. For example, the pituitary gland, which is located at the base of the brain, synthesizes growth hormone that regulates this process. The adrenal glands secrete adrenaline. This substance helps the body cope with stressful situations, mobilizing all its forces. The pancreas is mixed. It produces hormones that enter the bloodstream and directly into the cavity of internal organs (in particular, the stomach).
Digestive glands such as salivary glands and liver are exocrine glands. In the human body, they also include lacrimal, milk, sweat and others.
human digestive glands
These organs secrete enzymes that break down complex organic substances into simple ones that can be absorbed by the digestive system. Passing through the tract, proteins are broken down into amino acids, complex carbohydrates into simple ones, lipids into fatty acids and glycerol. This process cannot be carried out due to the mechanical processing of food with the help of teeth. Only the digestive glands can do this. Let's consider the mechanism of their action in more detail.
Salivary glands
The first digestive glands at their location in the tract are the salivary glands. A person has three pairs of them: parotid, submandibular, sublingual. When food enters the oral cavity, or even when it is seen, saliva begins to flow into the oral cavity. It is a colorless mucus-sticky liquid. It consists of water, enzymes and mucus - mucin. Saliva has a slightly alkaline reaction. The enzyme lysozyme is able to neutralize pathogens and heal wounds of the oral mucosa. Amylase and maltase break down complex carbohydrates into simple ones. This is easy to check. Put a piece of bread in your mouth, and after a short time it will turn into a crumb that can be easily swallowed. Mucus (mucin) coats and moistens food pieces.
Chewed and partially split food with the help of contractions of the pharynx through the esophagus enters the stomach, where it is further exposed.
Digestive glands of the stomach
In the most expanded part of the digestive tract, the glands of the mucous membrane secrete a special substance into its cavity - It is also a clear liquid, but with an acidic environment. The composition of gastric juice includes mucin, the enzymes amylase and maltase, which break down proteins and lipids, and hydrochloric acid. The latter stimulates the motor activity of the stomach, neutralizes pathogenic bacteria, and stops putrefactive processes.
Different food is in the stomach of a person for a certain time. Carbohydrate - about four hours, protein and fat - from six to eight. Liquids do not linger in the stomach, except for milk, which turns into curd here.
Pancreas
It is the only digestive gland that is mixed. It is located under the stomach, which determines its name. It secretes digestive juice into the duodenum. This is the external secretion of the pancreas. Directly into the blood, it secretes the hormones insulin and glucagon, which regulate. In this case, the organ works as an endocrine gland.
Liver
The digestive glands also perform secretory, protective, synthetic and metabolic functions. And it's all thanks to the liver. It is the largest digestive gland. Bile is constantly produced in its ducts. It is a bitter greenish-yellow liquid. It consists of water, bile acids and their salts, as well as enzymes. The liver secretes its secret into the duodenum, in which the final breakdown and disinfection of substances harmful to the body takes place.
Since the breakdown of polysaccharides begins already in the oral cavity, it is the most easily digestible. However, everyone can confirm that after a vegetable salad, the feeling of hunger comes very quickly. Nutritionists advise eating protein foods. It is energetically more valuable, and the process of its splitting and digestion lasts much longer. Remember that nutrition must be balanced.
And now you list the digestive glands? Can you name their functions? We think so.
2. 3. DIGESTIVE SYSTEM
(two lessons)
Lesson 1
DIGESTION IN THE MOUTH AND GASTROMA
2. List the digestive and non-digestive functions of the gastrointestinal tract (GIT).
Digestive - secretory, motor, absorption. Non-digestive - protective, excretory, production of biologically active substances, vitamins.
3. List the main patterns of the digestive system. What pattern of regulation of secretory function is manifested along the gastrointestinal tract in the cranial-caudal direction?
The adaptive nature of secretion (the dependence of the amount and composition of digestive juice on the composition of food), relay race, duplication and periodicity of functions. Reducing the role of the central nervous system and increasing the importance of humoral and local nervous mechanisms in the regulation of secretion.
4. Expand the meaning of the process of digestion.
The splitting of nutrients into species-free components that can be absorbed into the blood and lymph while maintaining their energy value.
5. What are the three types of food processing carried out in the process of digestion?
Mechanical (chewing, swallowing, mixing, moving food), chemical (enzymatic) and physicochemical (effect of hydrochloric acid, bile).
6. Name three types of digestion depending on the origin of enzymes.
Autolytic, symbiotic and own.
7. Explain the concepts: autolytic digestion, symbiotic digestion, own digestion.
Autolytic digestion is carried out through food enzymes, symbiont - through enzymes produced by intestinal microorganisms (symbionts), own - through enzymes synthesized by the digestive glands of the organism itself.
8. Give a classification of the types of digestion according to their localization. Which of them are leading in an adult?
Intracellular and extracellular. The latter is divided into abdominal and parietal (membrane) - leading in humans.
9. To what final components are proteins, fats and carbohydrates broken down in the digestive tract?
Proteins - to amino acids, fats - to glycerol and fatty acids, carbohydrates - to monosaccharides.
10. What class of enzymes are digestive enzymes? Why is their energy value preserved when polymers are broken down in the digestive tract?
to the class of hydrolases. Enzymes that hydrolyze nutrients do not break down the high-energy bonds of food molecules. At the same time, the main amount of energy remains in the products of hydrolysis, no more than 1% of the energy contained in food is released.
11. Name the functions of the food center. Specify the localization of its main components.
Formation and regulation of eating behavior, coordination of the digestive tract. Medulla oblongata, reticular formation, hypothalamus, limbic system, cerebral cortex.
12. Explain the concept of "sensory saturation." What causes it to happen?
A feeling of satiety of a reflex nature that occurs after eating as a result of excitation of the receptors of the mouth and stomach and the receipt of afferent impulses in the central nervous system, as a result of which the saturation center is activated and the hunger center is inhibited.
13. Explain the concept of "metabolic satiety". How long after eating does it occur?
Saturation resulting from the intake of nutrients into the blood. Occurs 1.5 - 2 hours after eating.
14. What is the essence of a chronic experiment and its advantage over an acute experiment in studying the physiology of digestion?
Studies are carried out periodically over a long period of time on intact or recovered animals after a preliminary operation. The conditions are as close to natural as possible.
15. Name the major human salivary glands. What kind of saliva does each of them produce?
Parotid, submandibular, sublingual glands. The parotid salivary gland produces serous saliva, the other glands produce serous-mucous saliva.
16. What device is used to study separately the work of large salivary glands in humans and who developed it?
With the help of Lashley-Krasnogorsky capsule. The method allows you to collect saliva separately from each salivary gland.
17. What types of food processing are carried out in the oral cavity?
Mechanical (chewing and moving food to the entrance to the esophagus), physicochemical (moisturizing and sliming the food bolus), chemical (initial stages of carbohydrate hydrolysis).
18. List the digestive functions of saliva.
Formation of a food bolus, enzymatic processing of food, participation in the assessment of its taste.
19. List the non-digestive functions of saliva.
Protective (bactericidal effect of lysozyme), participation in articulation, excretory, endocrine (kallikrein), thermoregulatory functions.
20. What is the main digestive enzyme of saliva and the substrate it acts on? In what part of the gastrointestinal tract is its action mainly carried out? What limits the time of action of this enzyme?
Alpha-amylase, for polysaccharides (starch); acts in the fundus of the stomach until the contents are mixed with gastric juice; the enzyme is inactivated in an acidic environment.
21. What irritants can cause the secretion of the salivary glands? What is the adaptive variability of the work of the salivary glands?
Any irritants acting on the oral mucosa (both food and rejected substances). In the change in the quantity and quality of saliva (viscosity, enzymatic activity) depending on the properties of the stimulus.
22. What is the main mechanism of regulation of the salivary glands? What general pattern of regulation of the secretory activity of the gastrointestinal tract is reflected in this fact?
Complex reflex mechanism (a set of unconditioned and conditioned reflexes). The role of the CNS in the regulation of the gastrointestinal tract is most pronounced in the cranial region and gradually decreases in the caudal direction.
23. Irritation of what receptors of the oral mucosa causes an unconditioned salivary reflex? Name the nerves that contain afferent fibers from the receptors of the oral mucosa.
Taste, tactile, temperature and other receptors of the oral mucosa. Trigeminal, facial, glossopharyngeal, vagus.
24. What is the duration of the latent period of the unconditioned salivary reflex? Compare with those of other digestive glands? What does this fact indicate?
1 - 3 s. The shortest latency period among the digestive glands. It indicates a high reactivity of the salivary glands.
25. What parasympathetic nerve innervates the submandibular and sublingual salivary glands? Which nerve branch is it?
The drum string is a branch of the mixed facial nerve (VII pair of cranial nerves).
26. What parasympathetic nerve innervates the parotid gland? Which nerve branch is it?
The auricular-temporal nerve is a branch of the trigeminal nerve (V pair of cranial nerves).
27. From which segments of the spinal cord and from which ganglion do the salivary glands receive sympathetic innervation?
From II - IV thoracic segments through the superior cervical sympathetic ganglion.
28. What is the difference between saliva released under the influence of parasympathetic nerves and saliva released under the influence of sympathetic nerves?
Parasympathetic nerves stimulate the secretion of a large amount of liquid, enzyme-poor saliva; sympathetic - a small amount of thick, rich in enzymes and mucus saliva.
29. What is the difference between the secret of the glands of the pyloric part of the stomach and the secret of the glands of its fundus?
The glands of the pyloric part of the stomach secrete a small amount of weakly alkaline juice with a high content of mucus, in the fundic part an acidic juice rich in enzymes is secreted.
30. List the substances that are part of the gastric juice that provide (1) physicochemical and chemical processing of food, (2) perform protective functions and (3) participate in hematopoiesis.
1) Hydrochloric acid and enzymes (mainly pepsins); 2) hydrochloric acid, lysozyme, mucoid; 3) internal factor of Castle.
31. Name the main types of exocrine cells of the gastric glands and the substances produced by them.
Glandulocytes (chief cells) produce pepsinogen; parietal glandulocytes (parietal cells) - hydrochloric acid and internal factor of Castle; mucocytes (additional cells) - mucus.
32. What enzymes are included in the composition of gastric juice and what subgroups are they divided into?
Proteolytic (actually pepsins, gastrixin, pepsin B) and lipolytic (gastric lipase).
33. How are gastric juice pepsinogens activated? What nutrients do pepsins act on, to what compounds do they break them down? Specify the optimal pH of the medium for pepsins in the fundus and antrum of the stomach.
hydrochloric acid and pepsins. Pepsins break down proteins, mainly to polypeptides. For pepsins of the fundus - 1.5 - 2, for pepsins of the antrum - 3.2 - 3.5.
34. What fats are available to the action of gastric lipase? What is it connected with?
Only emulsified fats (for example, milk fats), since there are no conditions in the stomach for emulsifying fats.
35. Name the functions of hydrochloric acid directly related to the physicochemical processing of food.
Causes swelling and denaturation of proteins, activates pepsinogens, creates an optimal environment for the action of pepsins, accelerates curdling of milk.
36. List the functions of hydrochloric acid that are not directly related to the physicochemical processing of food.
Regulates gastric motility, the work of the pyloric sphincter, promotes the formation of the Castle factor, has a bactericidal effect, inhibits the release of gastrin.
37. What is the protective effect of mucoids contained in gastric juice, what cells produce them?
Mucoids protect the gastric mucosa from mechanical and chemical influences. Produced by accessory cells (mucocytes).
38. What is intrinsic factor of Castle, where is it produced, by which cells, what effect does it have?
Gastromucoprotein, produced by parietal cells of the gastric mucosa (along with HCl); necessary for the absorption of vitamin B 12 involved in hematopoiesis.
39. How much gastric juice is excreted in a person per day? What is its pH value?
2 - 2.5 liters of gastric juice are secreted per day, pH = 1.5 - 2.0
40. Name the main methods for studying the secretory activity of the stomach in humans. For what purpose are they performed?
Sounding. In order to obtain gastric juice and subsequent study of its composition and pH, probe pH-metry.
41. List the main methods for studying gastric motility in humans.
Various options for x-ray examination, radionuclide methods, electrogastrography.
42. What are the phases of gastric secretion and secretion mechanisms in each phase?
The first is a complex reflex (brain), the second is gastric, the third is intestinal (the last two are neurohumoral).
43. Why is the first phase of gastric secretion called complex reflex? By whom and in what experiment was this proven?
Because it is carried out by conditioned and unconditioned reflexes. IP Pavlov in the experience of imaginary feeding.
44. Irritation of which receptor zones causes unconditioned reflex excitation of the gastric glands?
Irritation of the mucous membrane of the mouth, pharynx, stomach, duodenum and other parts of the small intestine.
45. Indicate the localization of receptor zones, the irritation of which leads to unconditioned reflex separation of gastric juice in the first phase of gastric secretion. Name the nerves that stimulate the secretion of gastric juice. Where are their centers located?
Mucous membranes of the mouth and pharynx. Wandering nerves. In the medulla oblongata.
46. In what experiment, on the basis of what facts, was it proved that the vagus nerves stimulate the secretion of gastric juice? What effect do sympathetic nerves have on the production of gastric juice?
In the experiment of I.P. Pavlov on a dog under conditions of imaginary feeding (the brain phase of gastric secretion) and transection of the vagus nerves: with intact nerves, gastric juice is released, with cut ones - no. Sympathetic nerves stimulate the synthesis of organic components of gastric juice.
47. What is the mechanism of excitation of the gastric glands when food enters the oral cavity? Describe the sequence of processes in the implementation of this mechanism.
Reflex. When food acts on the receptors of the oral and pharyngeal mucosa, afferent impulses enter the medulla oblongata, activate the centers of the vagus nerves, then the impulses along the centrifugal fibers of the vagus nerves enter the gastric glands, as a result of which gastric juice is released.
48. What experiments can prove the humoral mechanism of excitation of the gastric glands?
The introduction of hormones of the gastrointestinal tract into the blood, blood transfusion from a well-fed animal to a hungry one, monitoring the secretion of an isolated ventricle according to Heidenhain (denervated).
49. Name the groups of chemicals that stimulate the production of gastric juice.
1) Hormones of the gastrointestinal tract; 2) products of protein hydrolysis; 3) extractive substances of meat, vegetables.
50. What is the mechanism of excitation of secretory activity of the stomach in the second (gastric) and third (intestinal) phases of secretion? Describe the main stages of the implementation of this mechanism.
Neurohumoral; irritation of the chemo- and mechanoreceptors of the stomach and small intestine causes excitation of the centers of the vagus nerves, activation of gastric secretion and the release of gastrin and histamine. Other gastrointestinal hormones and parahormones, hydrolysis products, and extractives also participate in the process.
51. What is the difference between the secretion of the glands of the greater and lesser curvature of the stomach?
The lesser curvature glands produce juice that is more acidic and contains more pepsins than the greater curvature glands.
52. What is the adaptive variability of the work of the gastric glands expressed in?
The quantity and quality of gastric juice (amount of HCl, enzymatic activity, changes in secretion over time, duration of secretion) depend on the quality (bread, meat, milk) and quantity of food.
53. What food substances are the most powerful causative agents of gastric secretion? In what phase of gastric secretion do fats act on the secretory and motor functions of the stomach, and how do these functions change under their influence?
Extractives (meat broth, cabbage juice), egg yolk. In the intestinal phase; slow down.
54. In what parts of the gastrointestinal tract are regulatory peptides (hormones of the digestive tract) predominantly produced? What is their role in digestion?
In the mucosa of the antrum (pyloric) part of the stomach and in the proximal part of the small intestine. Carry out humoral regulation of secretory, motor and absorption functions of the gastrointestinal tract.
55. What effect does gastrin have on the motility and secretion of the stomach, small intestine, duodenum, gallbladder and pancreas?
Stimulates the secretion of the stomach, duodenum, pancreas, enhances the motility of the stomach, small intestine and gallbladder.
56. What hormones of the digestive tract stimulate the secretion of pepsinogens in the stomach?
Gastrin, bombesin, motilin, cholecystokinin-pancreozymin.
57. What hormones of the digestive tract inhibit the secretion of pepsinogens in the stomach?
GIP (gastric inhibitory polypeptide), VIP (vasoactive intestinal peptide), gastrons and enterogastrons.
58. What effect does cholecystokinin-pancreozymin have on the digestive system?
Stimulates the secretion of pancreatic and stomach enzymes, inhibits the secretion of hydrochloric acid in the stomach; stimulates contractions of the gallbladder.
59. What effect does bombesin have on the production of gastrointestinal hormones? List these hormones.
Increases the release of gastrin, cholecystokinin-pancreozymin, pancreatic polypeptide (PP) and neurotensin.
60. What effect does histamine have on the secretory activity of the stomach?
Histamine causes the secretion of a large amount of gastric juice with a low content of enzymes and high acidity.
Lesson 2
DIGESTION IN THE INTESTINE. MOTOR FUNCTION
DIGESTIVE TRACT. SUCTION
1. What is called digestion? What happens to the energy value of nutrients and their species specificity in the process of digestion?
A set of physicochemical processes that ensure the breakdown of complex nutrients entering the body into simple chemical compounds capable of assimilation without losing their energy value (but with a loss of species specificity).
2. What glands secrete their secret into the duodenal cavity?
Pancreas, liver, duodenal (Brunner's) glands.
3. What substances are broken down by pancreatic enzymes?
Proteins, fats, carbohydrates and products of their incomplete hydrolytic cleavage.
4. Name the pancreatic enzymes that break down proteins.
Trypsin, chymotrypsin, elastase, carboxypeptidases A and B.
5. List the pancreatic enzymes that hydrolyze fats, carbohydrates and nucleic acids.
Fats are hydrolyzed by lipase, phospholipase, lecithinase, esterase; carbohydrates - alpha-amylase, maltase, lactase; nucleic acids - ribonuclease, deoxyribonuclease.
6. What activates trypsinogen and chymotrypsinogen?
Trypsinogen is activated by enterokinase and trypsin, while chymotrypsinogen is activated by trypsin.
7. What substances act on and to what compounds do trypsin and chymotrypsin break them down?
On proteins and products of their hydrolytic cleavage, bringing the cleavage to oligopeptides and amino acids.
8. What substances does the lipase secreted by the pancreas act on and to what compounds? What and why is necessary for the high efficiency of this enzyme?
Breaks down fats into monoglycerides and fatty acids. Bile, because it emulsifies fats, dramatically increasing the surface area available for the action of fat-insoluble lipase.
9. What influence do parasympathetic and sympathetic nerves have on the amount and composition of the secreted pancreatic secret?
Parasympathetic nerves stimulate the release of a large amount of enzyme-poor secretion, sympathetic - a small amount of enzyme-rich pancreatic secretion.
10. Name the gastrointestinal and pancreatic hormones that stimulate its exocrine function.
Gastrin, secretin, cholecystokinin-pancreozymin, bombesin, substance P, insulin.
11. Name the gastrointestinal hormones and hormones of the pancreas that inhibit its exocrine function.
Pancreatic polypeptide (PP), enkephalin, somatostatin, GIP, glucagon.
12. What facts testify to the presence of humoral regulation of exocrine pancreatic activity?
A change in the secretory activity of the gland after the introduction of the corresponding hormone into the blood or blood transfusion from a well-fed animal to a hungry one.
13. List the main digestive and non-digestive functions of the liver.
Digestive - production of bile; non-digestive: antitoxic, excretory, thermoregulatory, synthesis of coagulation factors and other blood proteins, urea formation, destruction of various substances (hormones, hemoglobin); depot of blood, iron, vitamins A and D, carbohydrates; participation in the metabolism of proteins, fats, carbohydrates.
14. What is the antitoxic function of the liver?
In the neutralization of infectious agents and toxic substances that entered the body from the outside or formed during the interstitial exchange.
15. Name the main components of bile.
Bile salts, bile pigments, fatty acids, cholesterol, inorganic salts, enzymes, mucus.
16. List the digestive functions of bile.
Bile stimulates motility and secretion of the small intestine, bile formation and bile secretion, emulsifies fats, increases the activity of pancreatic and intestinal enzymes, neutralizes the acidic chyme of the stomach, promotes the absorption of fat hydrolysis products.
17. Is bile continuously or periodically formed and secreted into the duodenum? How much bile is secreted per day? How can you get bile for analysis in humans?
Bile is formed continuously, and is secreted periodically during meals and during digestion (0.5 - 1.0 liters per day). By probing the duodenum.
18. What is called the circulation of bile acids?
The bile acids released into the intestine ensure the absorption of fatty acids, after which 80-85% of the bile acids themselves are reabsorbed in the distal ileum, enter the bloodstream, are transferred to the liver and re-included in the bile for reuse.
19. Bile - secret or excretion? Justify your answer.
Bile is a secret involved in the process of digestion (for example, in the emulsification of fats), and excretion - in its composition, metabolic products (for example, bile pigments) are excreted from the body.
20. What is the difference between cystic bile and hepatic bile and why?
Cystic bile is more concentrated due to the reabsorption of water and mineral salts (bicarbonates), has a darker color.
21. List the reflexogenic zones from which bile formation and bile secretion are regulated by an unconditional reflex. What are the phases of bile secretion?
Mucosa of the mouth, stomach, small intestine. Complex reflex, gastric and intestinal.
22. What effect does the vagus nerve have on the contraction of the gallbladder and the sphincter of Oddi during bile secretion? What is the result of this influence?
Causes contraction of the gallbladder and relaxation of the sphincter of Oddi, resulting in the release of bile into the duodenum.
23. What hormones of the digestive tract stimulate the release of bile into the intestines?
Cholecystokinin-pancreozymin, gastrin, secretin, bombesin.
24. What foods stimulate the release of bile into the intestines?
Egg yolks, milk, meat, fats.
25. What type of secretion of intestinal juice occurs? What is the essence of this type of secretion?
Basically, according to the type of holocrine morphokinetic secretion, i.e., with rejection of the epithelium containing enzymes.
26. List the main enzymes of the juice secreted by the mucosa of the small intestine.
Peptidases, nucleases, lipase, phospholipase, phosphatases, amylase, lactase, sucrase, enterokinase.
27. What is called the "enzyme of the enzyme", where is it produced and what effect does it have?
Enterokinase is an enzyme produced in the small intestine that activates trypsinogen.
28. What is meant by membrane (parietal) digestion?
Digestion carried out by enzymes fixed on the glycocalyx and on the plasma membrane of the microvilli of the small intestine.
29. In what experiment can one prove the existence of membrane digestion?
In an experiment with the addition of pieces of live or boiled small intestine to a test tube with starch and amylase, as a result of which the hydrolysis of starch is sharply accelerated.
30. What is the origin of the enzymes involved in membrane digestion?
Part of the enzymes is adsorbed from intestinal juice, part is produced by enterocytes of the small intestine.
31. What is the adaptive (adaptive) nature of the secretory activity of the glands of the small intestine? List the enzymes of intestinal juice, the secretion of which has an adaptive character.
In changing the amount of juice and the relative content of individual enzymes or their groups in it, depending on the quantity and quality of food. Enterokinase, alkaline phosphatase, sucrase, lactase.
32. Specify the main features of the regulation of secretion of the small intestine.
In the regulation of secretion, the leading role belongs to local nervous mechanisms. The central nervous system has a trophic effect by regulating the formation of intestinal enzymes.
33. What is meant by local mechanisms of excitation of the intestinal glands?
Mechanisms implemented through local (peripheral) reflexes or under the influence of local humoral agents (tissue hormones of the gastrointestinal tract).
34. What irritants stimulate the secretion of small intestine juice upon contact with its mucosa?
Mechanical and chemical (components of intestinal contents).
35. How does the motor activity of the distal and proximal sections change in relation to this area with adequate stimulation of the intestinal area?
The stomach is a muscular organ, a kind of temporary reservoir for storing and processing food.
The stomach is the widest part of the alimentary canal. It is located under the diaphragm on the left side of the abdomen. The shape and size of the stomach changes depending on the amount of food taken. The stomach of an adult can hold up to 3 liters of food.
FUNCTIONS OF THE STOMACH
The stomach has powerful muscular walls that contract, crush and soften food, preparing it for processing in the intestines. In general, the stomach performs the functions of accumulation, mechanical and chemical processing, evacuation of food into the intestines.
STRUCTURE OF THE STOMACH
Actually myself stomach is a muscular organ.
Glands - some of which secrete mucus that protects the walls of the stomach from gastric juice, others secrete hydrochloric acid, and others secrete enzymes.
In addition to enzymes, mucus and hydrochloric acid, gastric juice contains a number of organic and inorganic substances.
The middle layer of the stomach wall is muscle membrane, consisting of smooth muscles, the contraction of which contributes to the mixing of food and soaking it with gastric juice.
TO annular muscle - sphincter located on the border between the stomach and the duodenum, which periodically opens and passes semi-digested food into the duodenum.
DIGESTION PROCESS
From the pharynx, the food bolus formed in the oral cavity enters the esophagus. The mouth of the esophagus is equipped with circular muscles that prevent the reverse movement of food from the stomach into the esophagus. Food enters the stomach crushed and soaked in saliva.
From the outer surface of the food bolus is exposed to the action of gastric juice, and inside it continues the action of saliva. Gradually, the food bolus breaks up and turns into gruel, which is processed by gastric juice.
glands. The lining of the stomach contains many glands. Some of them secrete mucus, which protects the walls of the stomach from the action of gastric juice and irritating food substances, others secrete hydrochloric acid.
The glands of the stomach secrete gastric juice, which digests food. There are glands that secrete the enzyme pepsin, which breaks down proteins. Hydrochloric acid not only creates the necessary environment for the enzyme to work, but also destroys many harmful microorganisms that have penetrated with food.
In the middle layer of the stomach wall there is a muscular membrane, consisting of smooth muscles, the contraction of which contributes to better mixing of food and soaking it with gastric juice. Gradually, the muscles push the food slurry to the duodenum. On the border between the stomach and the duodenum is an annular muscle - the sphincter. Periodically, it opens and passes semi-digested food into the duodenum.
The secretory activity of the stomach is greatly influenced by the emotional mood of a person. If you get a little nervous, your stomach will immediately react with heartburn, or vice versa, with indigestion.
Gastric juice- an integral part of the stomach. Gastric juice - digestive juice produced by the glands of the gastric mucosa; is a colorless transparent liquid with a sour taste.
The cells of the gastric glands are divided into main, lining and additional; each group produces certain components of the juice. Chief cells form enzymes that break down nutrients: pepsin, which breaks down proteins; lipase, which breaks down fat, etc. Parietal cells produce hydrochloric acid, which has a special and extremely important role in digestion: it softens the food bolus, activates enzymes.
Gastric juice kills microorganisms, enhances the production of enzymes by the pancreas, promotes the formation of digestive hormones. Its concentration in human gastric juice is 0.4-0.5%.
The acidity of gastric juice depends on the content of hydrochloric acid, on the rate of secretion of juice, on the neutralizing effect of gastric mucus, and changes in diseases of the digestive system.
The mucus secreted by the accessory cells imparts viscosity to the gastric juice; mucus has an alkaline reaction, neutralizes hydrochloric acid, reduces the acidity of the juice, protects the mucous membrane from irritation and is involved in the digestion of food.
In addition to enzymes, mucus and hydrochloric acid, gastric juice contains a number of organic and inorganic substances. It also contains a special substance (the so-called Castle factor), which ensures the absorption of vitamin B 12, which is necessary for the normal maturation of erythrocytes (red blood cells) in the bone marrow.
The digestive capacity of gastric juice secreted in different periods of secretion, as well as in different parts of the stomach, is not the same. IP Pavlov's research found that secretion is not continuous: under normal conditions, outside of digestion, gastric juice is not secreted into the stomach cavity.
This happens only under the influence of a food stimulus - not only when food enters the mouth or stomach, but often already from its smell, appearance, and even when talking about food. An unpleasant smell or type of food can, on the contrary, reduce or completely stop the secretion of gastric juice.
In diseases of the stomach, intestines, liver, gallbladder, etc., the amount of gastric juice and its composition can change up to the complete cessation of excretion and enzymes (achilia). The amount and composition of gastric juice can change with the emotional stress of a person.
DISEASES OF THE STOMACH
The most common diseases of the stomach are gastritis (inflammation of the gastric mucosa), and when the inflammation passes to the duodenum, another organ of the gastrointestinal tract, this is already called gastroduodenitis.
The main, and one of the main signs of problems in the stomach is a white or yellow coating on the tongue. Normally, the tongue should be a bright pink color with no signs of plaque. And if you are often accompanied by symptoms such as: heartburn, bad taste in the mouth, bad breath (not due to diseased tonsils, caries, etc.), constant fatigue, poor appetite, feeling of heaviness in the pit of the stomach after eating, So it's time to take your health seriously.
If a person has eaten poor-quality food, a gag reflex may occur and the contents of the stomach are thrown out.
OUR STOMACH LOVES:
1) Frequent fractional meals 5-6 times a day, in small portions, otherwise, you can stretch the stomach to a large size, resulting in a constant feeling of hunger. This is one of the main principles of a healthy diet.
2) Warm food(the food taken should be neither too hot nor too cold).
3) Thoroughly chewed food will not irritate the stomach, and it will also contribute to the sufficient secretion of digestive juices.
OUR STOMACH DOES NOT LIKE:
1) Irregular meals(1-2 times a day).
2) Dry food(hamburgers, hot dogs, chips, crackers, etc.).
3) Very hot food or very cold food.
4) Very spicy or fatty foods(mustard, pepper, vinegar, onion - in large quantities irritate the esophagus and stomach).
5) stress, can cause not only heartburn but also indigestion.
6) Alcohol
7) Smoking
8) Antibiotics(taking antibiotics disrupts the microflora of the stomach)
9) Bacteria "Helicobacter pylori", which damage the gastric mucosa and cause gastritis (found in 90% of patients).
10) Infections(Intestinal infections and chronic - oral cavity and pharynx (caries and inflammation of the tonsils).
11) Diseases gallbladder, liver, pancreas, since all these organs are interconnected and have a direct influence on each other.
