DIGESTION

Digestion - the breaking down of nutrients  into its monomers under the action of enzymes of the gastrointestinal tract.

Important
1) monomers have no specific specificity,
(2) monomers can be transported through cell membranes,
(3) monomers can be used immediately by cells for anabolism (synthesis of new ATP) and catabolism (oxidation and energy release). 

Essence of digestion: enzymatic hydrolysis (hydrolysis of proteins to amino acids, fats - to fatty acids and glycerol, carbohydrates - to monosaccharides).

Digestive functions of the gastrointestinal tract:
1) secretion, (2) motor(peristalstic expolsion food), (3) absorption.

Non-digestive functions of the gastrointestinal tract:
(4) protective, (5) excretory (for example, excretion of bilirubin), (6) endocrine (synthesis and secretion of gastrointestinal hormones into the blood), (7) antianemic (iron absorption, secretion of the internal factor of Castle for assimilation vitamin B12).

TYPES OF DIGESTION:
(1) Auto (digestive enzymes are formed in the body itself);
(2) symbiont (enzymes are formed by other organisms, for example, the microflora of the large intestine in humans); (
3) autolytic (enzymes are found in the food product, for example, lipase in the mother's milk during breastfeeding).
Types of digestion:
 (1) cavitary (in the stomach cavity, in the intestinal cavity under the action of digestive juice enzymes),
(2) parietal (on the surface of the epithelium of the small intestine by enzymes adsorbed or fixed in the cell membrane),
(3) intracellular epithelial cells of the intestine under the action of lysosomal enzymes).

DIGESTION IN THE CAVITY OF THE MOUTH
Motorics: capture and hold food, chewing, swallowing. Arbitrary and involuntary movements. Regulation is nervous, central (nuclei of the cranial nerves, striopallidal system, cortex of the cerebral hemispheres).
Secretion: 3 pairs of salivary glands. Parotid glands are serous. Submandibular and sublingual - serous and mucous (mixed). Saliva composition: water, mineral salts, amylase (enzyme that breaks down carbohydrates), lysozyme (bactericidal), mucus. Saliva is formed by the secretory cells of the acini (active and passive transport of substances from the plasma of the flowing blood) and is finally formed in the excretory ducts of the glands. The amount of saliva: 0.5-2 liters. Saliva functions: (1) physical processing of food (wetting, dissolving, forming a food lump, (2) chemical processing of food (digestion of carbohydrates), (3) protective function, (4) thermoregulation (by evaporation of water), (5) participation in the formation of speech, etc. (digestive and non-digestive).
The adaptive nature of the salivary glands: salivation depends on the quantity and quality of food and non-food (rejected) substances entering the oral cavity. For example, more saliva is allocated to the bread than to meat; salted bread is given out more than bread; on the dried powder of saliva is allocated more than a piece of biscuit, etc.

Regulation of salivation: CNS, a complex reflex mechanism (including conditioned and unconditioned reflexes) Parasympathetic nerves (medulla oblongata, facial and lympho-ocular nerves) stimulate salivation (many saliva, few organic substances), sympathetic nerves (spinal cord, thoracic segments 1-2) - reduce salivation (little saliva, a lot of mucus and enzymes).

REFERENCE ARC OF PARASIMPATIC REFLEX (draw the diagram): receptors of the oral cavity (tactile, taste, temperature) - sensitive fibers of the cranial nerves - salivary nuclei of the medulla oblongata - preganglionic parasympathetic fibers (mediator acetylcholine) - ganglia (near the gland or in itself) postganglionic parasympathetic fibers (mediator acetylcholine) - salivary gland (vasodilation, increased secretion).

REFLECTOR ARC SYMPATIC REFLEX - receptors of the oral cavity (as well as any others under stress!) - brain centers - spinal cord (T1-2) - preganglionic sympathetic fibers (mediator acetylcholine) - ganglia (sympathetic trunk) - postganglionic sympathetic fibers (neurotransmitter mediator ) - salivary gland (narrowing of the vessels, a decrease in secretion, dry mouth).
Methods of investigation: in animals - salivary gland fistula; in humans - the capsule-sucker Leschle-Krasnogorsky.

Digestion in the Stomach
In physiology, the division of the stomach is divided into two parts: the base (upper 2/3) and pyloric (lower 1/3). Features of the base department - depots of food (food in-va are not mixed, the outer layers of the chyme are shifted to the pyloric compartment by weak peristaltic waves with a frequency of 3 per min); secretion of all components of gastric juice (pH = 1-1.5). Features pyloricheskogo department - mixing, mashing and evacuation of chyme with strong peristaltic waves; secretion of slightly alkaline juice (pH = 3-3.5 because HC1 is not produced here); endocrine function (release of gastrin into the blood).

COMPOSITION OF THE GASTROID JUICE: (1) enzymes, (2) HC1, (3) mucus. (Quantity - 2-2.5 liters).
(1) Enzymes: pepsins - proteolytic (break down proteins). Isolated by the main cells of the gastric glands in an inactive form (pepsinogen), activated by HC1. Each of the seven pepsins has maximum activity at a certain pH value. Lipase - cleaves only the fat of milk (because they are already in an emulsified form) and only in a slightly acid medium
(2) HC1 - is secreted by the parietal (parietal) cells of the gastric glands. (These same cells distinguish the internal factor of Castle, which is necessary for the assimilation of vitamin B12).

THE SIGNIFICANCE OF SALTIC ACID: Denaturation and swelling of proteins; activation of pepsinogen; Creation of the optimal pH value for the action of enzymes;
bactericidal action; promotes the assimilation of iron (3-valent iron of plant products translates into a 2-valent form, which is easily digested);
is a chemical stimulus of the pyloric part of the stomach, 12 duodenal ulcer (as an irritant involved in the regulation of secretion, motility and endocrine function of the gastrointestinal tract).
(3) Mucus covers the wall of the stomach, has an important protective value (mucus components are not cleaved by enzymes).
The adaptive nature of gastric secretion: the duration of secretion, the digestive power of gastric juice, its amount - depend on the chemical and mechanical properties of food of animal and vegetable origin.

REGULATION OF VENTRIC SECRECTION
Phase 1 is cerebral. It is also called complex-reflex, because it involves conditional and unconditioned reflexes. The secretory nerve of the stomach is the vagus nerve (parasympathetic fibers). The secretion begins in 5-7 minutes and lasts 1-1.5 hours. It is allocated 20% of the total number of juice.
The scheme of the reflex arc: the receptors of the oral cavity - sensitive fibers of the cranial nerves - the medulla oblongata, the vagus nuclei - the preganglionic nerve fibers (mediator acetylcholine) - the ganglia (located intramurally, ie in the wall of the stomach itself) - the postganglionic nerve fibers Acetylcholine) - gastric glands Study method - experiments with "imaginary feeding" in dogs: the esophagus is cut, food does not enter into the stomach, and pure gastric juice for testing is obtained through the fistula of the stomach.
2 phase - gastric, neuro-humoral. Seed 70% of the total number of juice. The following mechanisms are involved: (1) nerve central (long reflex arcs: receptors of the stomach - sensitive pathways - oblong brain (vagus nuclei) - preganglionic nerve fibers - intramural ganglia - postganglionic nerve fibers - stomach glands. (2) nerve local (short reflex arcs (3) endocrine (gastrin, released into the blood by the endocrine cells of the pyloric part of the stomach, stimulates the secretion of HC1 by the glands of the fundus). (4) paracrine (histamine, It develops in all parts of the stomach, is secreted into the intercellular fluid, acts locally, on neighboring cells, stimulates the secretion of HC1) .The method of investigation is experiments with an isolated small ventricle: food enters the stomach through a probe (to exclude 1 phase), and pure gastric juice is obtained from a small isolated ventricle through a fistula.The isolated Pavlov's ventricle ("vagus") begins secretion in 5-7 minutes. Isolated ventricle of Heidenhain ("bezvagusny") begins secretion in 30-40 min. only humoral regulation (gastrin) remains.
Phase 3 - intestinal, neuro-humoral. It is allocated 10% of the total number of juice. Stimulation of gastric secretion continues with the participation of the vagus nerve (long reflex arcs), but the inhibitory effect of sympathetic peripheral reflexes, as well as duodenal hormones (secretin, cholecystokinin, GIP, VIP, etc.) appears.
The transition of chyme from the stomach into the 12-colon. The consistency of chyme in the pyloric department is estimated by mechanoreceptors (additional osmotic agents are the chemical and chemical properties of chyme). A powerful peristaltic wave is formed and the tone of the pyloric sphincter decreases. The portion of chyme passes into duodenum. Under the influence of HC1, the chemoreceptor of the duodenum develops a "reflex reflex" and the pyloric sphincter closes.

DIGESTION IN 12-PERSONAL SCRATCH.
Digestion continues under the action of (1) juice of the duodenal glands, (2) pancreatic juice, (3) bile.
Pancreas: weakly alkaline (bicarbonates present), rich in enzymes. Quantity - 1.5-2.5 liters.
Contains a set of enzymes for the breakdown of proteins, fats and carbohydrates.
Proteins are cleaved by trypsin, chymotrypsin, elastase, carboxypeptidase (up to polypeptides, oligopeptides and free amino acids). These enzymes are released in an inactive form. Their activation begins under the action of a special enzyme of intestinal juice - enterokinase ("enzyme enzymes").
Fats are split by the action of lipase, phospholipase.
Carbohydrates are cleaved under the action of amylase.

REGULATION OF PANCREATIC SECRECY
Phase 1 - cerebral, reflex. The secretory nerve is n.vagus (mediator acetylcholine
Is allocated 10-15% of the total number of juice.
Phase 2 - gastric, neuro-humoral. Secretion is stimulated by the vagus nerve and gastrin (the hormone of the stomach). It is allocated 10% of the total number of juice.
Phase 3 - intestinal, neuro-humoral. Secretion stimulates the vagus nerve and duodenal hormones secretin, cholecystokinin. It is allocated 70-80% of the total number of juice.
Secretin is secreted by the endocrine cells of the duodenum into the blood (under the action of HC1) and stimulates the secretion of pancreatic juice (water and bicarbonates - to neutralize HC1). Cholecystokinin is secreted by the endocrine cells of the duodenum into the blood (under the action of the products of the cleavage of proteins and fats) and stimulates the synthesis and secretion of pancreatic enzymes.
Liver: biliary and biliary excretion.
Three important observations: (1) bile is formed constantly, but is released periodically (therefore accumulates in the gallbladder); (2) bile contains no digestive enzymes;
(3) bile is both a secret and an excreta.

COMPOSITION OF YELLOW: bile pigments (bilirubin, biliverdin are toxic products of hemoglobin metabolism. They are excreted from the internal environment of the body: 98% with bile from the gastrointestinal tract and 2% by the kidneys); bile acids (secreted by hepatocytes); cholesterol, phospholipids, etc. Hepatic bile is weakly alkaline (due to bicarbonates).
In the gallbladder, the bile concentrates, becomes very dark and dense. The volume of the bladder is 50-70 ml. In the liver, 5 liters of bile is produced per day, and 500 ml is released into the 12-colon. Stones in the bladder and in the ducts are formed (A) with an excess of cholesterol and (B) a decrease in pH during bile congestion in the bladder (pH <4).
(1) emulsifies fats, (2) increases the activity of pancreatic lipase, (3) promotes the absorption of fatty acids and fat-soluble vitamins A, D, E, K, (4) neutralizes HC1, (5) exerts bactericidal action, (6) ) performs excretory function, (7) stimulates motor and absorption in the small intestine.

CIRCULATION OF GILT ACIDS: Bile acids are used many times: they are absorbed in the distal part of the ileum (ileum), flow into the liver with bloodstream, are captured by hepatocytes and again excreted into the intestines as bile.

REGULATION OF BONDING: neuro-humoral mechanism. The wandering nerve, as well as gastrin, secretin, bile acids increase the secretion of bile.

REGULATION OF BREEDING: neuro-humoral mechanism. The wandering nerve, cholecystokinin causes a contraction of the gallbladder and relaxation of the sphincter. Sympathetic nerves cause relaxation of the bladder (accumulation of bile).

NON-ALLEGED FUNCTIONS OF LIVER: (1) protective (detoxification of various substances, synthesis of urea from ammonia), (2) participation in the metabolism of proteins, fats and carbohydrates, (3) inactivation of hormones, (4) blood depots, Digestion in the small intestine
The functional unit is the crypt and the villi. The nuzzle is the outgrowth of the intestinal mucosa, the crypt is the opposite, a depression.
Intestinal Fluid weakly alkaline (pH = 7.5-8) is composed of two parts: (a) the liquid portion of the juice (water, salt, without enzymes), is secreted by cells of the crypts; (B) dense part juice ( "mucous clumps") is composed of epithelial cells that continuously exfoliated from the top of the villi. (Entire mucous membrane of the small intestine is completely renewed after 3-5 days). In the dense part there are more than 20 enzymes. Part of the enzyme adsorbed on the surface glycocalyx (intestinal, pancreatic enzymes), enzymes other part is a part of the cell membrane microvilli .. (microvilli - it outgrowth cell membrane microvilli of enterocytes form a "brush border" that significantly increases the area, in which the hydrolysis and. suction). Enzymes are highly specialized, necessary for the final stages of hydrolysis.
In the small intestine, there is cavitary and parietal digestion.
Cavity digestion - the splitting of large polymer molecules to oligomers in the intestinal cavity under the action of enzymes of intestinal juice.
Pristenochnoe digestion - splitting oligomers to monomers on the surface of microvilli under the action of enzymes fixed on this surface.

THE SIGNIFICANCE OF THE SURGERY DIGESTION: (1) high hydrolysis rate,
(2) in a sterile environment. microbes do not penetrate into the "brush border" and can not be fed with hydrolysis products, which (3) are immediately absorbed, because The final stages of hydrolysis are associated with the transport of monomers through the cell membrane to the enterocyte.
Regulation of secretion in the small intestine. The main mechanism of regulation is local nervous, due to the submucosal plexuses of the enteral nervous system. The reflex arcs are closed intramural, in the intestinal wall. (The effects of sympathetic and parasympathetic nerves are long-term, adaptive).
Humoral regulation: (a) paracrine (also local) and (b) endocrine (has a long-term, adaptive character).
STUDY intestinal secretion in animal studies performed by intestinal fistula (fistula Thiry-Vella): both ends of the isolated intestinal loop are displayed on the surface of the abdominal wall. The mesentery with the vessels and nerves passing through it is preserved. Isolation of intestinal juice from the fistula occurs only in response to irritation of the mucosa of the isolated loop of the small intestine (local nervous regulating mechanism).

THE MOTHER OF THE small INTESTINE
(1) Tone, slow tonic waves. Myogenic regulation (the ability of smooth muscles to be automated, which is amplified in response to the stretching of myocytes).
(2) Stirring (non-propelling) movements: (a) rhythmic segmentation (periodic reduction of small areas of the annular muscles); (b) pendulum movements (periodic contraction and relaxation of the longitudinal muscles).
(3) Advancing (peristaltic) movements. Peristalsis is a complex coordinated contraction of the circular and longitudinal muscle layers involving the exciting and inhibitory neurons of the enteric nervous system. As a result, the chyme moves in a strictly defined direction - from the oral end of the gastrointestinal tract to the anal.
(In the large intestine, there is also an antiperistaltic, ie, the movement of the chyme in the opposite direction).
Parasympathetic nerves increase intestinal motility, sympathetic nerves-brake.

SUCTION IN THE THIN INTESTINE
The nuzzle is the suction organ. The nuzzle is covered with a layer of enterocytes, inside it are the blood and lymphatic capillaries, the nerve fiber. The nail works like a pump by reducing and relaxing the smooth muscle cells.
At the heart of absorption are the mechanisms of active and passive transport of substances through the cell membrane of enterocytes.
Passive mechanisms: filtration, diffusion, osmosis.
Active mechanisms: primary-active transport (mainly potassium-sodium pump in the basal part of the membrane); secondary-active transport (sodium-dependent transport in the apical part of the membrane) and endocytosis.
Glucose is a secondary-active sodium-dependent transport to the enterocyte and facilitated diffusion from the enterocyte into the intercellular fluid and then into the blood.
Amino acids - four transport systems for different groups of amino acids, working on the same principle. In addition, there are similar transport systems for tri- and dipeptides.
Monoglycerides and fatty acids - in the lumen of the intestine are included in the composition of micelles, consisting of bile acids and phospholipids. In such a complex are delivered to the suction surface (microvilli of enterocytes). The products of fat splitting, dissolving in the cell membrane, pass into the enterocyte, where neutral fats are synthesized from them. Then, in combination with proteins (chylomicrons), fats enter the lymphatic capillaries of the villi. The bile acids remain in the lumen of the intestine, they are reused and absorbed into the blood in the distal ileum (ileum).
To study the absorption in the experiments on the live

DIGESTION IN THICK INTEGRAL
There are no naughts, there are only crypts. Liquid intestinal juice contains practically no enzymes. The mucous membrane of the large intestine is renewed for 1-1.5 months.
Important is the normal microflora of the large intestine: (1) fermentation of cellulose (short-chain fatty acids are formed, which are necessary for feeding the epithelial cells of the colon itself); (2) decay of proteins (in addition to toxic substances, biologically active amines are formed); (3) synthesis of B vitamins; (4) suppression of growth of pathogenic microflora.
In the large intestine, water and electrolytes are absorbed, as a result of which a small amount of dense masses are formed from the liquid chyme. 1-3 times a day a powerful contraction of the colon leads to the movement of the contents into the rectum and its removal outward (defecation).


What is digestion?
The importance of digestion for the body.
What is the chemical process underlying digestion?
What are the initial and final products of digestion?
Name 3 digestive functions of the digestive tract.
What are the non-digestive functions of the digestive tract?
What digestive processes occur in the oral cavity?
What nutrients are split in the oral cavity?
Name three pairs of large salivary glands.
The composition of saliva.
Functions of saliva.
Name the enzymes of saliva. What kind of nutrients they split?
What determines the amount and composition of saliva?
What is the adaptive nature of salivation?
Why is the regulation of the salivary glands called a reflex reflex?
Innervation of the salivary glands.
Influence of parasympathetic nerves on salivation (mediator?)
The influence of sympathetic nerves on salivation (mediator?)
The scheme of the reflex arc of the salivary reflex.
Methods of studying salivation in animals and humans.
Composition of gastric juice.
Characteristics of gastric juice enzymes.
The value of hydrochloric acid.
Features of secretion in the fundus and pyloric department of the stomach.
Three phases of gastric secretion.
Name the secretory nerves of the stomach.
What is gastrin? How does it affect gastric secretion?
What is secretin? How does it affect gastric secretion?
What is cholecystokinin? How does it affect gastric secretion?
How does the transition of the chyme from the stomach into the 12-colon proceed?
The secret of which glands enters the 12-colon?
Composition of pancreatic juice.
Why does pancreatic juice have a slightly alkaline reaction?
Three phases of pancreatic secretion.
Name the secretory nerves of the pancreas.
How do secretin and cholecystokinin affect pancreatic secretion?
Composition of bile.
The meaning of bile.
What is the difference between gallbladder and hepatic bile?
Where does bile formation occur? How is it regulated?
How does biliary excretion occur? How is it regulated?
What is the circulation of bile acids?
Intestinal juice. Its features.
What is parietal digestion?
The value of parietal digestion.
The main mechanism of regulation of secretion in the small intestine.
Is the secretion of intestinal juice from the fistula Tiri Vella, if the food is in the mouth?
Is the secretion of intestinal juice from the fistula Tiri-Vella, if the food is in the stomach?
Is the secretion of intestinal juice from the fistula Tiri Vella, if the normal process of digestion occurs in the main part of the small intestine?
What is the absorption in the small intestine?
What mechanisms are the basis of absorption?
How does glucose uptake occur?
How does the absorption of amino acids occur?
How does the absorption of fat-splitting products occur?
What features of secretion in the large intestine?
What features of motility in the large intestine?
What are the features of absorption in the large intestine?
The importance of the microflora of the large intestine.