Physiology Of Digestion: Stages, Organs, Enzymes

The physiology of human digestion is not easy. Once ingested, food takes part in various physical and chemical processes. It is these stages that make up digestion in the body. They are attended by different bodies, which have their own role.

Dietary enzymes play an important role in the process of digestion. These elements are responsible for the coherence of everything that happens: from the oral cavity to the small intestine. If these biological catalysts fail, it immediately affects the well-being.

Physiology of digestion

Man needs energy to live. Most of it is formed as a result of digestion. It is of several types:

• Autolytic. Digestion with the help of enzymes that are part of food. pH 3.5 – yield of lysosomal enzymes.

• Hydrolysis. Depolymerization of protein, fats and carbohydrates with the help of specific enzymes. Cleavage of intermolecular bonds with water.

• Symbiotic. Enzymes of bacteria and protozoa: digestion of dietary fiber, proteins, fats, synthesis of vitamin B, amino acids, absorption of vitamin D.

• Own. Enzymes of the digestive organs: extracellular (cavity), intracellular, membrane (parietal).

• Extracellular. in the organ cavity. Depolymerization. Most active in the KDP. Parietal in cell membranes.

• Intracellular. Molecular and vesicular.

Stages of the digestion process:

1. Grinding in the oral cavity.

2. Swallowing and advancing.

3. Admission to the stomach and deposition.

4. Entering the duodenum and neutralizing the acid.

5. Enzymatic degradation of substrates.

6. Delivery of nutrients to the liver and through the lymph to the bloodstream.

7. Transport of nutrients in tissues.

8. Completion of digestion in the large intestine with the help of microflora.

The structure of the digestive system:

• oral cavity;

• pharynx;

• oesophagus;

• stomach

• small intestine;

• colon.

The digestive system also includes the salivary glands, liver, gallbladder, and pancreas.

Grinding processes in the oral cavity

Processes occurring in the oral cavity:

1. Chopping food.

2. Wetting food with saliva.

3. Taste analysis.

4. initial hydrolysis.

1.5 liters of saliva is secreted per day. Hydrolysis of starch - alpha-amylase.

Food entering the mouth irritates taste, tactile and temperature receptors. There is a reflex activation of the secretion of the stomach, pancreas, excretion of bile and intestines, as well as the inclusion of motility of the entire gastrointestinal tract.

Chewing features:

• Chewing.

• Wetting with saliva.

• Formation of a food bolus.

• Duration 15 seconds.

The beginning of the digestive system is divided into 2 sections: the vestibule and the cavity. From below it is limited by the diaphragm of the mouth (maxillary-hyoid muscles). Above - hard and soft palate. From the sides - cheeks. Front lips. Behind - pharynx and communication with the pharynx.

Structure: crown, neck, root. Enamel is covered from above - 95% calcium, phosphate and calcium carbonate and cement - 28% organic matter (collagen). Inside is the pulp, as well as the artery, nerve and vein.

• Milk teeth - 20.

• Molar teeth - 32 (6 - 13 years - 26 years).

An elongated flattened muscular organ: own muscles (upper and lower longitudinal, transverse, vertical) and skeletal muscles (geniolingual, hyoid-lingual, stylolingual). Front top. Behind - the body of the tongue, passing into the root of the tongue. The upper convex surface is the back of the tongue.

The mucous membrane of the tongue is velvety, without plaque, cracks, clearly visible papillae. At the root of the tongue, there may be a seal - the lingual tonsil - an immune organ, part of Pirogov's pharyngeal lymphoid ring.

Language features:

• Determining the taste of food.

• Participation in the mechanical processing of food.

• Participation in the act of swallowing.

• participation in articulation.

• Closure of the airways during swallowing.

Distinguish:

• Small salivary glands (1 - 5 mm): in the thickness of the mucous and submucosal bases of the oral cavity. Labial, buccal, molar, palatine, lingual.

• Large salivary glands: located outside the walls of the oral cavity, but open into it with excretory ducts.

• Parotid 25 g - steam room - in front and below the auricle.

• Submandibular - steam room - submandibular triangles of the neck.

• Sublingual - steam room - excretory ducts under the tongue.

Saliva moisturizes food, moistens the oral cavity, has a bactericidal effect (lysozyme), digestion of polysaccharides with the help of beta-amylase. Saliva pH is neutral, 99.5% water.

The act of swallowing

Swallowing is a complex reflex process, the transfer of the food bolus into the esophagus with the overlap of the airways.

A huge number of receptor formations in the mucous membrane along the esophagus trigger a chain of reflex acts until the food leaves the esophagus and the next phase of digestion begins.

The contraction of the esophagus has the character of a wave. It spreads towards the stomach. Consistent reduction of the circular layer. Speed ​​2 - 5 cm / s - depends on the properties of the food bolus. Vagus enhances peristalsis and reduces the tone of the cardia.

The structure of the throat:

• On the front wall - choanae, pharynx, below the larynx.

• On the inner wall is the pharyngeal tonsil.

• On the lateral - pharyngeal opening of the auditory tube - tubal tonsils.

• Three divisions: nasopharynx, oropharynx and laryngopharynx.

• Muscles: constrictors (compressors and lifters of the pharynx).

The act of swallowing is a continuous alternation of the following phases:

• the muscles of the soft palate contract, the palatine curtain rises and presses against the vault and the back wall of the pharynx, separating the nasopharynx from the rest of the pharynx;

• when the muscular diaphragm of the mouth contracts, the larynx rises and moves forward, the epiglottis closes the entrance to the larynx;

• when the styloid and hyoid-lingual muscles contract, the root of the tongue moves back, the food bolus is pushed through the pharynx into the oropharynx;

• due to the contraction of the palatoglossal muscles, part of the food bolus that has entered the oral part of the pharynx is separated (cut off) from the food that is still in the oral cavity;

• when a food bolus enters the pharynx, the longitudinal muscles lift it, pulling it onto the food bolus;

• consecutive downward contraction of the pharyngeal constrictors pushes the food bolus from the pharynx into the esophagus.

The structure of the stomach

The stomach is located between the esophagus and the duodenum. Food stays in it for 4-6 hours.

• Digestion: protein - pepsin and hydrochloric acid and fat.

• Absorption: sugar, alcohol, water, salts.

In the mucosa, an anti-anemic factor (Casla) is formed - the binding and adsorption of vitamin B12.

The shape of the stomach depends on the physique, the type of food taken and the position of the body. The length of the empty stomach is 20 cm, width 8 cm. Capacity 1.5 - 4 liters.

The structure of the stomach:

• The cardia is where the esophagus enters the stomach.

• The bottom or vault is on the left.

• The body of the stomach is the greater and lesser curvature.

• The pyloric part (pylorus) is the pyloric cave and the pylorus canal.

• The border is a circular groove (valve) and the pyloric sphincter.

• 3 layers of muscles: outer - longitudinal, middle - circular, inner - oblique.

• Motility - mixing chyme.

More detailed consideration:

• On the lesser curvature - the path of the stomach.

• On the bottom and body - transverse, longitudinal and oblique folds.

• On the mucosa of the gastric fields - a granular appearance of the mucosa.

• Gastric pits with excretory ducts of the gastric glands.

• 1 mm mucosa - 60 gastric pits.

• The total number of pits is 35 million.

• Endocrine cells: serotonin, melatonin, histamine, glucagon, somatostatin, VIP.

In a newborn, it has the shape of a cylinder or a bull's horn. Cardiac part, fundus and pyloric part are weakly expressed, pylorus is wide. The volume of the stomach is about 50 cm3.

At the end of the 1st year of life, the length of the stomach reaches 9 cm, the width is 7 cm, and the volume increases to 250-300 cm3. At the age of 2 years, the volume of the stomach is 490-590 cm3, 3 years - 580-680 cm3, by 4 years - 750 cm3. By the end of the period of the second childhood (12 years), the volume increases to 1300-1500 cm3.

In children who are bottle-fed, the stomach is stretched, especially in the anterior wall. A significant part of the stomach of a newborn (cardia, bottom, part of the body) is located in the left hypochondrium and is covered by the left lobe of the liver.

Substances of gastric juice:

• Inorganic substances: water, chlorides: sulfates, bicarbonates of sodium, potassium, magnesium.

• Hydrochloric acid.

• Organic: proteins - enzymes, mucoproteins, mucoproteases.

Functions of hydrochloric acid:

• Protein denaturation.

• subsequent breakdown of proteins.

• Activation of pepsinogens.

• Creation of an acidic environment.

• Antibacterial action.

• Regulation of food bolus promotion.

• Participation in the regulation of the secretion of the stomach, pancreas and duodenum.

• Stimulation of enterokinase synthesis.

• Stimulation of motor activity of the stomach.

Mucin - protects the wall from chemical and thermal damage, autolysis. Isolation by mucosal cells. Composition: water + glycoproteins + IgA + bicarbonates + oligo and polysaccharides. Castle factor - glycoprotein (antianemic factor) - absorption of vitamin B12.

Mucus is a unique substance that provides protection against damage and infection by preventing agglutination. Sialomucins - activity against viruses.

Scheme of action of enzymes

Enzymes are biological catalysts that have the ability to activate various chemical reactions that occur in a living organism. They are of a protein nature. Enzymes are synonymous with the term enzymes.

The action of enzymes is strictly specific, that is, each enzyme catalyzes only one or a few close chemical reactions.

Their name is made up of the name of the substance on which they act, and the ending "aza".

The name can consist of the name of the substance on which the enzyme acts, plus the type of reaction and the ending "aza"

An enzyme can have a trivial name

The main functions of enzymes:

• Accelerate the transformation of substances that enter the body and are formed in the process of metabolism (to renew cellular structures, to provide processes with energy, etc.).

• Regulate biochemical processes (for example, the implementation of genetic information).

The scheme of action of enzymes:

1. Formation of an enzyme-substrate complex.

2. The transformation of a substrate into a product: the breaking of old bonds, the formation of new ones.

3. Release of the product from the complex.

Enzyme activators:

• Organic: bile acids, glutathione, cysteine, vitamin C.

• Inorganic: hydrochloric acid, many metal ions.

Enzyme Inhibitors:

• reversible inhibition. Often these substrate-like substances are used as medicines.

• Irreversible inhibition: concentrated acids and alkalis, salts of heavy metals, ultraviolet irradiation, cell poisons.

Enzyme classification

• Oxidoreductases catalyze redox reactions. Enzymes of this type carry H atoms or electrons. Many oxidoreductases are enzymes of respiration and ATP synthesis. These are dehydrogenases, oxidases, oxygenases.

• Transferases catalyze the transfer of functional groups (methyl-, sulfur-, amino-, etc.) from one molecule to another. These are kinases.

• Hydrolases catalyze the hydrolytic cleavage of bonds (peptide, glycosidic, ether, phosphodiester, etc.) (with the participation of H2O). These are peptidases, esterases, glycosidases, phosphatases.

• Lyases - cleavage of bonds between C, O, N, S atoms with the participation of H2. These are decarboxylases, aldolases, dehydrotases.

• Isomerases catalyze the formation of isomers, including cis-, trans-isomerization, the movement of multiple bonds, as well as groups of atoms within a molecule. These are mutases, cis-trans isomerases, racemases, epimerases.

• Ligases (synthetases) catalyze synthesis reactions using the energy of ATP.

Enzymes are simple and complex. Simple - in the form of simple proteins (hydrolases). Complex: apoenzyme (protein) + cofactor (non-protein bond).

Digestive and external enzymes

Digestive Enzymes:

• Amylase

Produced by the salivary gland. In the oral cavity, the primary process of fermentation, the breakdown of food, begins. Produced by the pancreas (hydrolyzes the polysaccharide in the duodenum). Breaks down starch and glycogen to mono- and disaccharides (maltose, glucose). Inactive in gastric juice.

• Proteases

A class of enzymes that break down proteins. Produced by the stomach, pancreas and intestinal secretions. In the stomach, the enzyme pepsin begins its work (active at pH 2).

• Lactase

It is secreted by the small intestine to break down milk sugar into glucose. Genetically determined lactase deficiency occurs in approximately 16% of the population in Russia.

• Lipase

Carries out the splitting of fats into glycerol and higher fatty acids. It is synthesized by the pancreas for the duodenum and small intestine, where the breakdown of fats occurs. With a lack of bile and / or lipase, underdigested fats reach the large intestine, causing irritation of its walls, becoming one of the causes of irritable bowel syndrome.

• Enzymes from outside

All raw plant foods contain active enzymes. Fermented foods contain a lot of enzymes (especially a lot of digestive enzymes).

Lipase is found in excess in "raw" plant-based fatty foods such as avocados, seeds, and nuts. There are much more enzymes in sprouts than are necessary for their assimilation. Pineapple, mango, papaya are especially rich in enzymes. Ginger contains zingabain, which can break down proteins. Honey improves the breakdown and subsequent absorption of almost all basic substances (starch, sucrose, proteins) that come with food, with the exception of fats.

Sections of the small intestine

Sections of the small intestine:

• DPC - from the pylorus to the duodenal flexure LII - the shape of a horseshoe - the upper (bulb), descending (Vater's papilla), horizontal and ascending parts.

• Skinny.

• Iliac - mesenteric part - 14 - 16 loops in the umbilical region.

Food that has undergone high-quality processing in the oral cavity and stomach enters the small intestine.

Endocrinocytes produce serotonin, cholecystokinin, and secretin. Paneth cells secrete erepsin.

In the mesenteric part of the small intestine, especially in the ileum, there are 40-80 Peyer's patches, which are clusters of single lymphoid nodules that are organs of the immune system.

3 common diseases of the small intestine and their treatment

Dumping syndrome (from the English. Dumping - reset) - a syndrome consisting in the accelerated movement of the contents of the stomach into the intestines without proper digestion (surgery, low acidity, impaired motility, impaired blood supply).

Symptoms:

• Feeling hot.

• Salivation.

• Diarrhea.

• Bloating.

• Hyperemia of the face.

• Hot sweat.

• Tachycardia.

• Hyperglycemia.

Dumping syndrome correction:

• Restriction of simple carbohydrates to 120 g / day: sugar, cereals, muffins.

• Protein diet (at least 1.5 g per kg).

• Pectins.

• Eat slowly.

• Do not drink while eating! Don't eat soups.

• Drink no earlier than 30 minutes after eating.

• Lie down after eating.

Giardia (guardia, giardia) is a unicellular flagellated parasite. Giardia cysts can remain alive for almost 3 months. Mode of transmission: Primary waterway, but outbreaks are rare. Ways of infection: contact, household and food ways. The duration of the incubation period is up to 25 days.

lamblia lives in the duodenum and upper jejunum and causes:

• mechanical traumatization of the intestinal mucosa;

• violation of the intestinal biocenosis;

• the formation of secondary enzymatic deficiency;

• subatrophy and atrophy of the mucosa of the small intestine, leading to malabsorption syndrome;

• impaired motility of the small intestine (reflux pathology) due to irritation of the nerve endings of the intestinal wall;

• violation of the binding of bile acids, manifested by a change in motility not only of the small intestine, but also of the biliary tract, skin itching.

Be sure to specify the place of stay, symptoms and morbidity of the environment.

Forms of chronic course (many cases of asymptomatic or latent course):

• A variant with a predominant lesion of the digestive system, including dyspepsia syndrome, irritable bowel syndrome, dysfunction of the sphincter of Oddi, gastroduodenitis.

• A variant with a predominant lesion of other organs and systems, including anemia, allergic dermatitis, allergic rhinitis, asthenovegetative syndrome.

• Mixed option.

Atypical forms: giardia carrier, subclinical.

The final diagnosis of giardiasis is established on the basis of the detection of giardia cysts or trophozoites in feces or duodenal contents.

Since cysts are isolated intermittently and are sometimes absent (“blind period”), 3-fold microscopy of feces with an interval of 2–3 days is recommended.

The effectiveness of the study is increased by taking laxatives and / or choleretic drugs 1-2 days before the study, delivery of feces to the laboratory no later than 15-20 minutes later. after defecation.

Serological diagnostic methods are indirect. It is impossible to make a diagnosis and prescribe only on the basis of a positive serological reaction, without examining fecal samples.

The preparatory stage of treatment is from 2 to 4 weeks.

In nutrition, the amount increases:

• vegetable fiber;

• protein food;

• foods that increase acidity (systematic use of cranberries, lingonberries).

An important place is given to the appointment of choleretic drugs, while preference is given to cholekinetics and cholespasmolytics (a high concentration of bile in itself has a detrimental effect on many protozoa, and also restores gastrointestinal motility).

Antispasmodics, enzyme preparations (according to indications).

Eradication stage:

• Metronidazole - within 5-7 days.

• Furazolidone is taken orally after meals. The course of treatment is 7 days.

• Macmirror - a course of 7 days. Efficiency 96.8%.

• Albendozol - relevant for mixed infections (for example, ascariasis, enterobiasis).

• Tinidazole - a course of treatment 1-2 days. Efficiency 70–80%.

• Ornidazole - taken once at night. Efficiency 90-92.5% with a one-day course.

After 10 days and after 1 month. after the end of etiotropic treatment - 3 control studies of feces for Giardia cysts with an interval of 1-2 days.

Overgrowth is diagnosed in many diseases of the gastrointestinal tract: gastritis, GU, DZHVP, cholecystitis, cholelithiasis.

Causes of SIBO:

• Hypochlorhydria (PPI).

• Biliary insufficiency.

• exocrine insufficiency.

• Refluxes (valve insufficiency).

• Dysbiosis as a result of metabolic syndrome.

• Intestinal diverticula.

• Small intestinal parasitosis.

• Immunodeficiencies.

Symptoms are numerous and not always specific, and SIBO is rarely isolated from other gastrointestinal pathologies. But the beginning of recovery with the correction of the microbial landscape of the duodenum is very important.

Absolute enzyme deficiency: damage to most of the pancreatic tissue (cell destruction, cysts and pseudocysts). Secondary enzyme deficiency: pH drop in the duodenum below 5.5 - enzyme inactivation, duodenal dyskinesia - impaired mixing, SIBO - inflammation and enzyme inactivation, deficiency of bile and enterokinase - impaired enzyme activation.

Maldigestia - a violation of the processes of digestion, accompanied by dyspeptic syndrome - manifestations of impaired digestion.

Malabsorption is a complex of disorders caused by malabsorption of nutrients, vitamins and microelements in the small intestine.

Malabsorption + maldigestion = malnutrition syndrome. Dyspeptic syndrome: pain, flatulence, dumping syndrome.

Malabsorption: polyfecal, steatorrhea, acholia, lactase deficiency, weight loss, muscle atrophy, pastosity, pallor, dry skin, decreased bone mineral density, symptoms of beriberi, anemia, polyglandular deficiency.

Maalbsortia syndrome is primary and secondary.

Primary - hereditary and congenital disorders of the structure of the small intestine and fermentopathy.

Secondary:

• Enterogenous (organic and functional).

• Pancreatogenic (chronic pancreatitis, pancreatic cancer).

• Gastrogenic (atrophic gastritis, gastric resection, gastrinoma, gastric cancer).

• Hepatogenic (cholestatic liver disease, cirrhosis).

Normalization of the state of the pancreas:

• Complete exclusion of alcohol, sour, spicy, fried.

• Mechanical processing of food.

• Heat treatment: boiling, stewing, steaming.

• Maximum restriction of animal fats!!!

Per day:

• protein - 100 -150 g;

• fat - no more than 65 -70 g;

• carbohydrates (starch) - 500 g or more.

Absolute indications for the appointment of enzymes:

• Underweight (BMI <18.5 kg/m2).

• Fat intolerance in a daily amount of less than 50 g.

• Steatorrhea and/or creatorrhea.

• In feces, elastase 1 is below 200 µg/g.

Functions of the large intestine

Main functions:

• Completion of the digestion process.

• Absorption of water and minerals, B vitamins, fiber hydrolysis products.

• Mechanical movement of feces.

• endocrine activity.

• Immune - an abundance of diffuse immune tissue.

The large intestine is a breeding ground for microorganisms. Most residents are anaerobic. Increasing the amount from the stomach to the distal gastrointestinal tract.

Degradation of carbohydrates and breakdown of proteins: CO2, methane, hydrogen sulfide, toxic substances (phenol, indole, cresol).

When antibiotics are used, the microbial landscape changes due to the multiplication of yeasts, staphylococci, clostridia, etc.

Normally, the chyme only travels in one direction. And bacterial contamination is impossible

After the stomach, food enters the small intestine, and from there into the large intestine. With increased intra-abdominal pressure, the valve between the small and large intestines may close.

The large intestine consists of the caecum, colon, sigmoid, and rectum. The caecum takes part in digestion, unlike the colon, which is mainly responsible for the absorption of fluid and electrolytes.

No less important digestive organs

The largest gland of soft elastic consistency. Length 30 cm, width 21 cm, height 7 - 15 cm. Weight 1500 - 1800 g. Diaphragmatic and visceral surfaces. Front and back edges. Two parts: right and left.

The unit of the liver - a lobule - is prismatic 1 mm in diameter. There are about 50 thousand slices in total. Consists of radially diverging hepatocytes.

A pear-shaped organ located in the right hypochondrium. Length 10 cm, width 5 cm, capacity 40 cm3. 3 departments: bottom, body - bend - neck. Adjacent to duodenum and colon. The main function is the accumulation and concentration of bile.

Point of the gallbladder: the connection of the 8th and 9th costal cartilages or the intersection of the costal arch with the right edge of the rectus abdominis muscle.

An elongated organ located retroperitoneally. Length - 15 cm, width 7 cm, thickness 2 - 3 cm. Weight - 90 g. It is located transversely to the left at the level of LII - LIII. Iron of mixed type. Exocrine part: 700 ml of juice. The endocrine part is insular.

The head of the pancreas, like a horseshoe, is surrounded by the duodenum. It also adheres tightly to the transverse colon, aorta and IVC, the celiac plexus, and the tail to the spleen.

The digestive system is a very complex mechanism. It is influenced by the work of other organs, hormones, diet and other factors. In order for digestion to be normal, a person must take care of his body and, in particular, what foods are eaten.

Doctors do not recommend overeating, including a lot of fatty and fried foods, as well as meat in the diet. These foods clog the body and do more harm than good. "Junk" food cannot give the body enough energy, but leads to the formation of excess weight. To protect yourself from digestive problems, you should now take care of a proper and balanced diet.