LESSON 1

Theme: Digestion.

Questions for self-control:

1.Digestion as the initial stage in metabolism. I.P. Pavlov’s contribution to the research of this issue.

2.Digestion of food in the mouth cavity, stomach and intestinal.

3.Chemical composition, saliva enzymes, gastric and intestinal juices.

4.Absorption of products of digestion. Definition of membrane digestion.

5.Diagnostic importance of biochemical analysis of gastric juice.

Currency of theme. A doctor must know the peculiarities of the process of digestion in normal and pathological conditions; must be able to estimate biochemical composition of gastric juice because violation of digestion and mechanisms of regular absorption may cause the following:

- hypotrophy with violation of self-reproduction of parts of the body;

- hypovitaminosis with the development of pathological conditions without distinct clinical manifestation;

- beriberi – the illnesses with distinct clinical presentation as the result of complete absence of vitamins in the organism;

- allergic conditions connected with the preservation of protein specifics and the increase of permeability of biological membranes in the cells of gastrointestinal tract.

The ability to detect pathological components of gastric juice may be used while diagnosing lesions of gastrointestinal tract during the initial stages of disease.

Educational and pedagogical aims.

1. The main object of the lesson: to work out skills of using the knowledge of biological role of gastric juices and mechanisms of food splitting in the mouth cavity and the ventricle (in the process of practical work of a physician).

  1. The by-objects of the lesson: to form the skills of qualitative and quantitative detecting of hydrochloric acid in gastric juice, the skills of evaluation and interpretation of the results of biochemical analysis of gastric juice.

Annotation of the theme:

Digestion.

Digestion is the complex of the processes which support the mechanical decomposition and chemical (fermentative, first of all) disintegration of nutritive matter into the components which are suitable for absorption and taking part in metabolism.

What is the biological significance of digestion and what are the aims of digestion?

1)The transformation of polymeric compounds into monomeric compounds:

proteins – amino acids

carbohydrates – monosaccharide

fats – higher fatty acids and glycerine

2)While being digested, the food looses its specifics.

The main types of digestion.

1)Extracellular (cavernous, distant) 2) Intracellular 3) Membrane or parietal

Saliva. Saliva is educed by excretory ducts (1,5 litre a day). pH is 6,5-6,9, it is subacid, its ductitility is 1,2-2,4 units.

The following buffer systems are in saliva: protein, haemoglobin, phosphate.

Saliva’s composition: 99,42 percent of water; 0,58 percent of organic and inorganic substances.

Inorganic substances: salt Ca, phosphates, compounds of Na and K, chlorides, bicarbonates, fluorides, rhodonites and etc.

Organic substances: proteins, carbohydrates, free amino acids, vitamins and others.

Organic substances (by its origin) are divided into those which generate into saliva from blood serum (amino acids, urea) and those which are synthesized by salivary glands (amylase, glycoprotein, mucin, globin and others).

The basis of organic substances is protein – 17 fractions.

Enzymes. There are 5 groups of enzymes.

Carbonic anhydrase, esterase, proteolytic enzymes, enzymes of mixed group – more than 50. Phosphatase, lipase, lysozyme, hyaluronidase, DNase, ribonuclease.

Functions.

Protective: moisturizes, prevents from drying up (mucin), from cracks and mechanical irritants, assists in wetting of food debris, micro organisms and prolongs their vital activity; bactericidal effect of lysozyme, lipase, DNase, ribonuclease.

Digestive: the formation of bolus and digestion of carbohydrates.

Composition of gastric juice. Water, HCl, mucous substances, inner factor of Kastle, histamine, gastrin, pepsin, lipase, renin, 35 million of glands which generate about 2,5 litre of gastric juice a day.

HCl – produces parietal cells of ventricle under the influence of gastrin.

Its role:

- to activate pepsinogen

- acts as antiseptic

- provides pH medium 1,5-2,5

- assists in swelling and denaturation of proteins

- stimulates the generation of secretin in duodenum

Types of HCl:

- free HCl

- combined HCl (to proteins and the products of their digestion)

- total HCl (free HCl and combined HCl)

- total acidity (all acid reacting components of ventricle – free HCl, combined HCl, organic components, calcium phosphate salts).

Mucous substances. The basis of mucous substances are glycoproteins (mucoproteins, mucopolysaccharides). They prevent the walls of the stomach from denaturated effect of HCl and from digestive effect of pepsin; also they have antiseptic action.

Inner factor of Kastle. Glycoprotein, formed in the mucous substances of the stomach, is necessary for the normal absorption of B12 in the bowels (intestinal), which comes into it with the food. The absence of the factor leads to malignant anemia.

Histamine. Histamine is formed in the mucous substances of the stomach; it provides the secretion of HCl and pepsin affecting the parietal and the cellula principalis of the stomach.

Gastrin. It is a polypeptide formed in the walls of the stomach. It affects the parietal and the cellula principalis of the stomach stimulating the excretion of HCl and pepsinogen.

Pepsin. Polypeptide disintegrates native denaturized proteins, generates the cellula principalis of the stomach under the influence of gastrin, and splits the peptide bonds which were formed by aromatic amino acids.

Gastricsin. Polypeptide, the optimum is pH=3,5. It provides the adaptation of the organism to the specifics of nutrition (vegetal food).

Lipase. It is inactivated in the organisms of grown-ups by acid medium. It is able to hydrolyze triglycerides of milk in the organisms of infants in case of the following factors: pH=5,0 or emulsified fat.

Rennin. It clots the milk in organisms of infants.

Different forms of HCl have definite constants which may change in different pathological conditions or they may increase and decrease.

The N (norm) of free HCl – 20-40 milimole per litre; more than 40 – hyperchlorhydria, less than 20 – hypochlorhydria, 0 – achlorhydria.

N of total acidity is 40-60 milimole per litre; more than 60 – hyperacidity, less than 40 – hypoacidity, 0 – non-acid condition (the absence of HCl and pepsin leads to achylia).

Composition of intestinal juice.

Pancreas juice is generated under the influence of secretin in duodenum and pancreozymin.

pH=7,1-8,2 1,5 litre per day

1. Enzymes affecting proteins – trypsin, chemotrypsin, enterokinase, carboxypeptidase, collagenase, elastase - turn into peptides and dipeptides.

  1. Enzymes affecting carbohydrates – amylase, sucrose, lactase, maltase, amino 1,6 glycosidase, oligo 1,6 glycosidase.
  2. Enzymes affecting lipids – lipase, emulsified lipids CO2 which are generated in the process of neutralization of HCl by bicarbonates. After that bile acids split them into diglycerides and take them to the stomach.
  3. Enzymes affecting nucleic acids – ribonucleic acid, desoxyribonucleic acid.

Bowels (intestinal).

pH=7,0-8,5 1,5 litre per day

  1. aminopeptidase, dipeptidase, cathepsins – dipeptides

2. aminopeptidase, dipeptidase, cathepsins + invertase – disaccharides, monosacchrides

3. lipase, esterase, cholesterolesterase – mono glycerin, glycerin – into the stomach

  1. phosphatase, nuclease, nucleotidases.

Defensive mechanisms in mucous substances of stomach.

1. Enzymes are generated in non-active form.

2. Mucin – mucous substances.

3. Defensive barrier (molecules of fat (lipids) with fumes). It is filled with water; it is situated on the external part of epithelial cell. If in normal condition, spirit and water may pass this barrier. This barrier may be destroyed only by detergents. The natural detergents in the organism are bile acids, which may pass into the stomach while reflux. Bile acids outwash fat.

4. The regeneration of epithelial cells of the walls of the stomach occurs in 3-5 days.

LESSON 2. (Control lesson)

Theme: Digestion.

Questions for self-control:

  1. Digestion as the initial stage in metabolism. I.P. Pavlov’s contribution to the research of this issue.
  2. Digestion of food in the mouth cavity, stomach and intestinal.
  3. Chemical composition, saliva enzymes, gastric and intestinal juices.
  4. Absorption of products of digestion. Definition of membrane digestion.
  5. Diagnostic importance of biochemical analysis of gastric juice.

LESSON 3.

Topic: Exchange and functions of carbohydrates.

Questions for self-control:

  1. Carbohydrates, their spread, their biological role.
  2. Classification of carbohydrates. Their composition:

a)monosaccharides and their derivatives (trioses, pentoses, amino sugar, uronic acids, glycosides, phosphoric ethers, monosaccharides);

b)disaccharides (lactose, maltose, saccharose);

c)polysaccharides: glycoproteins, proteoglycans, glycolipids, inulin, gum, pectic substances, agar.

  1. Proteoglycans. Their biological role.
  2. Glycoproteins. Sialic acids. Their biological role.
  3. Glycated protein. Glycated hemoglobin.
  4. Digestion and absorption of carbohydrates in the gastrointestinal tract. The role of cellulose. Intolerance of carbohydrates.

Carbohydrates are hydroxyl aldehyte or ketonospirits.

Functions of carbohydrates.

  1. Energy.
  2. Carbohydrates (ribose, deoxyribose) are in the composition of nucleic acids (deoxyribonucleic acid, ribonucleic acid), free mononucleotides (adenosine triphosphate, guanosine triphosphate, cyclic adenosine monophosphate, etc.), co-enzymes (nicotine amide adenine dinucleotide, nicotine amide adenine dinucleotide phosphate, flavin adenine dinucleotide, KoQ).
  3. Structural: glucoproteins – collagen; proteins – receptors; glycocalix, proteins defining blood group; factors of blood coagulation; enzymes; hormones; glycosaminglycans, etc.
  4. Defensive: immunoglobulin, interferon, mucins, fibrinogen, glycosaminoglycan, etc.
  5. Disintoxicating: they are in the composition of phospho-adenosin-phospho-sulfate and uridine diphosphate.

Daily maintenance is 500 gram.

Classification.

The first class is monosaccharides. They are derivatives of polyatomic spirits containing aldehyde and ketonic groups. Depending on the quantity of carbonic atoms, monosaccharides are divided into: trioses, tetroses, petoses (ribose, deoxyribose), hexoses (glucose, galactose, fructose, etc.).

Derivatives of monosaccharides:

- uronic acids: glucoronic acid, galactouronic acid). They are in the composition of glycosaminoglycans.

- amino sugar: glycosamin, galactosamin). They are in the composition of glycosaminoglycans.

- pentose (ribose or deoxyribose which are binding to nitrous basis in nucleotide by N-glycosoid bond). They are in the composition of RNA, DNA, ATP, NAD, FAD and others.

- phosphoric ethers of monosaccharides – substitution of hydrogen atoms into remains of phosphoric acid: glucose-6-phosphate; fructose-1,6-diphosphate; ribose-5-phosphate and others.

The second class is oligosaccharides. They are composed of 2 or more monosaccharides (from 2 to 10 remains of monosaccharides).

Disaccharides:

- maltose consists of 2 molecules of L-D-glucose which are linked by L-1,4-glycoside bond. It has free semi-acetal hydroxyl. It has renewing effect.

- lactose (lactic sugar) consists of B-D-galactose and L-D-glucose which are linked by B-1,2-glicoside bond. It has free semi-acetal hydroxyl. It has renewing effect.

- saccharose consists of L-D-glucose and B-D-fructose which are linked by L-1,2-glycoside bond. It hasn’t hydroxyl and that’s why it has no renewing effect.

The third class is polysaccharides. They contain more than 10 remnants of monosaccharides. They are divided into homopolysaccharides and heteropolysaccharides.

Homopolysaccharides consist of one and the same monosaccharide.

Starch and glycogen consist of L-D-glucose remnants.

Cellular tissue (cellulose) consists of B-D-glucose remnants which are linked by B-1,4-glycoside bond.

The role of cellular tissue.

  1. Irritating the nerve ending of mucous tunic (coat) of intestinal, it intensifies the peristalsis of intestinal.
  2. It increases the secretion of intestinal juice.
  3. It assists in forming of fecal mass.
  4. It adsorbs cholesterol, preventing its suction.
  5. It adsorbs heavy metals and radionuclides.
  6. Being affected in the intestinal by spirit fermentation, it suppresses the breeding of putrefactive bacteria.

Heteropolysaccharides consist of different remnants of monosaccharides and their derivatives. There are the following types of heteropolysaccharides:

  1. glycoproteins; 2. glycolipids; 3. proteoglycans.

Proteoglycans are complex proteins which consist of proteins and carbohydrates. Carbohydrates which are in the composition of proteoglycans are called glycosaminoglycans.

Classification of glycosaminoglycans.

1)hyaluronic acid, 2) chondroitin-4-sulfate, 3) chondroitin-6-sulfate,

4) dermatansulfate, 5) keratansulfate, 6) heparinsulfate and heparin.

They are widely spread in the organism of a man. Skin, tendon, cartilages, bones, synovial fluid, vitreous body, eyes, cornea, umbilical cord, mucous membrane of the mouth, nose, bronchus, blood vessels and so on.

Functions.

1.Defensive-mechanical.

2.They are biological cement. Filling the intercellular substance, they strengthen the connective tissue, prevent the penetration of harmful substances and morbific micro-organisms into the organism.

3.They possess high hydrophylia, that is, they restrain water and cations, assisting in regulation of water-salt metabolism.

4.They posses high viscosity, alleviate the process of swallowing, take part in the formation of a bolus.

5.Heparin is a natural anticoagulant (prevents the process of blood coagulation).

Composition. Hyaluronic acid consists of monomers, possessing glucuronic acid, linked with N-acetyl-D-glucosamine. Heparin consists of monomers, which possess glucuronic acid, linked with N-acetyl-D-glucosamine and 2 remnants of sulfuric acid.

For example, structure of heparin:

p

Digestion and absorption of carbohydrates in gastrointestinal tract.

The source of carbohydrates in the human body is food carbohydrates, the main of which is starch. Also, there is glucose, sucrose, lactose and fructose in food. Starch is the form of glucose depositing in the cells of plants. Lactose is in the composition of milk and it is the principal carbohydrate in infant’s nutrition. There is glucose and fructose in honey and milk. Maltose comes in with the products in which starch is partially hydrolyzed, for example, with malt or beer. The norm of carbohydrates in nutrition is 400-500 gram per day. Food carbohydrates undergo enzymatic digestion in the gastrointestinal tract. In the process of digestion, enzymatic hydrolysis of glycosidic linkage takes place, monomers (able to be absorptive) are generated, they are able also to get into blood and after that into tissues. Starch is partially absorbed in the mouth cavity under the influence of a-amylase saliva, after that, by pancreatic amylase, in the upper part of small intestine. The products of reaction are maltose and isomaltose, which are (with other disaccharides) hydrolyzed on the surface of small intestine cells to appropriate monomers. Monosaccharide transport from lumen of intestinal into the mucous membrane cells may be realized by means of reduced diffusion and active transport.

Glucose coming from intestinal by means of portal vena system gets to liver, where one portion of it is detained and another portion by means of general circulation gets into the cells of other organs and tissues. Glucose consumption by circulation cells occurs with the help of reduced diffusion with the assistance of carbohydrates-transporters. Thus, the speed of trans-membrane flow of glucose depends only on gradient of its concentration. The exceptions are the cells of muscles and adipose tissue, where reduced diffusion is regulated by insulin.

Pathology of carbohydrates digestion and absorption.

There are 2 reasons for the pathology of carbohydrates digestion and absorption:

- defect of enzymes taking part in carbohydrate hydrolysis in the intestinal,

- derangement of food absorption into the cells of intestinal mucous membrane.

Inherited and acquired forms of deficiency of enzyme activity are known. The symptoms of inherited forms are revealed even after the first breast-feeding (when there is deficit of lactase enzyme), after transition to artificial feeding or when adding sugar and starch into the ration (deficit of a-amylase or specific disaccharidase).

Acquired forms of pathology may be revealed when a person has intestinal diseases: gastritis, colitis, enteritis.

Lactase activity of a grown-up person is lower than of a child. That’s why the decrease of lactase activity may be revealed with the help of the symptoms of milk intolerance. The average rate of this pathology in the African countries is up to 97 percent, in Europe – 7-12 percent.

Derangement of absorption may be the result of carbohydrate-transporter deficiency in the system of monosaccharide transport through membrane.

When having all these conditions, diarrhea may occur. Intestinal microorganisms make carbohydrates split and organic acids and gases generate. The inflow of water in the intestinal increases, intestinal contents increases, and peristalsis is intensified. All these conditions lead to spasms, pains, flatulence and profuse diarrhea.

LESSON 4.

Topic: Exchange and functions of carbohydrates.

Aim of the lesson:To work out skills of using the knowledge of carbohydrates exchange in the organism (in the practical work of a doctor).

Questions for self-preparation:

  1. The general scheme of the sources and ways of consumption of glucose in the organism.
  2. Glycogen as the main reserved polysaccharide. Its properties, spread, biosynthesis, and mobilisation of glycogen.
  3. Glucose content in blood. Hypo-, hyperglycemia, glycosuria, reasons.
  4. Regulation of glucose level in blood. The role of CNS, the mechanism of the action of insulin, adrenalin, glucagons, glucocorticoid.

Considerable part of glucose, which enters the blood, turns into glycogen – reserve polysaccharide, which is used in the intervals between food intakes as the source of glucose.

Exchange and functions of carbohydrates.

Glycogen is animal starch. It is the main reserve homopolysaccharide. It consists of L-D-glucose connected with L-1,4 and L-1,6 by glycosidic linkage – (C6H10O5)p. Glycogen may be found in all organs and tissues. Its content in the liver is from 2 to 6 percent; in the muscular tissue – 0,5-2 %. Coloured reaction with iodine – brown colouring.

There is no enzyme gluco-6-phosphatase in the muscular tissue, that’s why glycogen gives no glucose to the muscular tissue, but is oxidized to lactic acid and 2 ATP (glycogenalisis).

Aglycogenosis is an inherited disease connected with the absence of enzymes which take part in glycogen synthesis. Glycogen is absent.

Glycogenosis is an inherited disease connected with the deficit or complete absence of enzymes which take part in glycogen decomposition. Glycogen in this case is stored in the organs and tissues.

The 1st type – hepatic:

Girke’s disease – the absence of enzyme glucose-6 phosphatase.

Gers’s disease – the absence of enzyme phosphorylase “a”.

Glycogen decomposition in the liver is violated and it is stored there. The liver enlarges, it is tight and painful while palpating. There is hypoglycaemia in blood in the periods between food intakes. Anderson’s disease – the absence of branching enzyme. Glycogen is synthesized but with the changed structure (in the shape of long threads). It causes the destruction of hepatocytes, liver cirrhosis, hepatic failure and leads to fatal outcome (children live up to 2 years).

The 2nd type – hepatic:

Mac Ardle’s disease – the absence of enzyme phosphorylase. Glycogen is stored both in skeletal muscle and cardiac muscle (megalocardia).