This document discusses digestion, beginning with an overview of the significance of digestion in breaking down food and absorbing nutrients. It then outlines the main types of digestion and the functions of the gastrointestinal tract. Specific sections are dedicated to describing digestion in the oral cavity, the composition and role of saliva, and the mechanism of salivation. Digestion is initiated in the mouth through mechanical and chemical breakdown aided by saliva secreted from salivary glands in response to stimuli in the oral cavity.

1. Topic name:
Digestion and its significance. Types
of digestion. Digestion in the oral
cavity.
Lecture plan:
 Digestion and its meaning, types of digestion.
 Functions of the gastrointestinal tract.
 Digestion research methods.
 Digestion in the oral cavity.
 Saliva, its composition and properties.
 The mechanism of saliva formation. Regulation, phases of salivation.
Translated by Darya Goryacheva, assistant of the Department of Physiology norms

2. Digestion and its significance
• Energy and plastic materials enter
the body with food. Nutrients,
other than mineral salts and
water, are mechanically and
chemically processed in the
gastrointestinal tract.
• In the process of digestion, large-
molecular organic substances are
converted into simple substances,
monomers, which are absorbed
into the blood and lymph and
absorbed by the body.
crushing
liquefaction,
dissolution
denaturation
depolymerization
to oligomers
depolymerization to
monomers
suction 6-10
liters
Food 800-1000 g
Water 1.2-1.5 l
Saliva –
0.5-2 l
Gastric juice –
2-2.5 l
Bile –
0.5-1 l
Pancreatic juice –
1.5-2 l
Small intestine juice
1.5-2 l
Colon juice -
0.05-0.06 l
Feces: 0.15-, 025 l of water,
50-100 g - food debris,
bacteria, epithelium

3. Main types of digestion
1. Autolytic: enzymes can be absorbed through food (breast milk).
2. Symbiotic: enzymes are produced by bacteria - hydrolysis by
enzymes of microorganisms (in the large intestine).
3. Own type of digestion
a) cavity (distant) digestion - the hydrolytic action of enzymes is realized in the
cavities of the digestive tract.
b) parietal (contact, membrane) digestion - an increase in hydrolytic processes
takes place in the mucous layer and in the area of the brush border of
enterocytes.
c) intracellular (phagocytosis, pinocytosis).

4. Functions of the gastrointestinal tract
1. Digestive.
The secretory function is the secretion of
digestive juices.
• There are 3 groups of enzymes:
1) proteases that break down proteins;
2) lipases that digest fats to glycerides
and fatty acids;
3) carbohydrases, which digest
carbohydrates to polysaccharides, di-
and monosaccharides.
Motor function.
Suction function.
Excretory function.
2. Endocrine function.
• In the cells of the mucous membrane of
the stomach, intestines, pancreas, active
substances (gastrointestinal hormones) are
synthesized, which exert their effect by
entering the blood.
• Hormones of the enteric system provide:
1) enhance or inhibit the secretion of
digestive juices.
2) act on metabolism - assimilation, on the
growth and development of a growing
organism.
3) have a trophic effect, improve the blood
supply to organs, and increase the
permeability of biological membranes.

5. Digestion research methods
To study the digestive function in humans, clinical methods are used: introduction
of a probe, radiography, electrogastrography, radiotelemetric technique,
endoscopy, the method of introducing radioactive isotopes, ultrasound, etc.
І. Experimental
vivisection
isolated organs
chronic experiences
I. Pavlov and his co-workers developed operations to obtain all digestive juices in
conditions of chronic experience - fistula operations.
II. Clinical and physiological

6. Digestion in the oral cavity.
• The digestion process begins in the mouth. Food in the oral cavity is 15-30
seconds. During this time, food is subjected to mechanical, physical, and
chemical processing.
Functions of the oral mucosa
1. Secretory.
2. Protective.
3. Regenerative.
4. Suction.
5. Reflexogenic zone

7. Saliva, its composition and meaning
• Saliva is a mixed secret secreted by 3 pairs of salivary glands (parotid,
submandibular, sublingual and many small glands).
• A person produces 600-1500 ml of saliva per day, an average of 1.0-
1.2 liters.
Oral cavity
Trachea
Resting state
Epiglottis
Tongue
Esophagus
The act of swallowing

8. Saliva composition
1. Enzymes:
• Salivary amylase (-amylase) - initial hydrolysis of
polysaccharides - to dextrans - disaccharides
• Maltase released during prolonged chewing -
disaccharides - disaccharides to monosaccharides.
2. Mucin
3. Lysozyme
Traces:
• Proteins, globulins, amino acids.
• Uric acid, urea, creatinine
• Enzymes: proteases, peptides, lipase, nuclease,
alkaline and acid phosphatases, etc.
1. Ions of potassium, sodium,
calcium, magnesium.
2. Phosphates, chlorides,
sulfates, bicarbonates.
3. Rhodonous compounds.
4. Iodide, bromide, fluorine,
trace elements: iron, nickel,
lithium
 Saliva is a digestive juice, slightly colorless, viscous, opalescent liquid.
 The specific gravity is 1.001-1.002. pH = 5.8-7.4.
 Water - 99.4-99.5%.
 Dry residue - 0.5-0.6%
Organic substances Inorganic substances

9. Dry food (crackers, meat powder) produces more
saliva than milk.
A lot of liquid saliva is released on the rejected
substances (sand, acid).

10. Salivation mechanism
• Afferent impulses from the
receptors in the oral cavity go to
the center of salivation in the
medulla oblongata along the
afferent fibers of the trigeminal,
facial, glossopharyngeal and
vagus nerves. From there along
the efferent fibers to the salivary
glands along the sympathetic
and parasympathetic nerves.

11. When sympathetic nerves are irritated, sympathetic
saliva is thick, rich in organic compounds, not
abundant. With irritation of the parasympathetic
nerves - chordal - liquid, abundant, rich in minerals.

12. Reflex mechanism of saliva secretion
• 2 phases of salivation:
1. Conditioned reflex phase. The separation of saliva occurs before
food enters the oral cavity at the sight of food, smelling, memories
of food, etc. It is carried out with the help of the cortex and the
center of salivation.
2. Unconditioned reflex phase. The separation of saliva occurs when
food enters the oral cavity, the receptors of the oral cavity are
irritated. Along the afferent nerves, impulses reach the center of
salivation and from there along the secretory nerves to the salivary
glands.

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