Digestion in oral cavity and stomach

1. Department of physiology

2.  Digestion is complex physiological process,
initial stage of exchange of substances and
energy in the organism.
 During the digestive process the food loses its
specific features and is transformed (broken
down) into simple components:
proteins  amino acids; carbohydrates  glucose;
lipids (fats)  free fatty acids and cholesterol.

3. Digestive system is made up of gastrointestinal tract
(GI tract) or alimentary canal and accessory organs,
which help in the process of digestion and
absorption.
GI tract is formed by
two types of organs:
1. Primary;
2. Accessory.

4.  Maintaining of homeostasis.
 Maintaining required level of metabolism and
energy exchange in organism.
 Excretory function – excreting some end
products with excrements (feces).
 Hormonal function – producing some
hormones and biologically active substances.
 Significant role in process of erythropoesis.
 Takes part in the process of adaptation of
organism.

5.  Mechanical processing of the food – formation of
smaller pieces (fragmentation), mixing and
propelling the food throughout the gastro-
intestinal tract (GI tract).
Term motility refers to the contraction of GI walls.
 Secretion of digestive juices – the enzymes in
them dissolve (broke down) proteins,
carbohydrates and fats.
 Absorption – the process of transport of the end
products of digestion, water, salts and vitamins
through the epithelial mucous membrane of GI
tract into blood and lymph.

6. The food is ingested via
mouth that is the initial part
of digestive system.
The oral part of digestive
system has attitude to the
intake of food, analysing
of its features, preparing
of food for chemical
digestion and propelling
it to the esophagus.

7.  Mechanical processing of the food (done by
chewing and swallowing acts).
 Partial chemical processing of the food.
 Partial absorption of the food.
 Protective function – it is a primary barrier against
the infectious agents that come with food.
 Trophic (nutritive) function.
 Sensory – approbation, sensation of food
properties.

8. Chewing (mastication) is a
physiological act during which
the food is being fragmented,
moistened by saliva, mixed
and partially chemically
processed.
As a result of chewing there is a
formation of digestive bolus. In
the act of chewing such organs
take part: upper and lower jaws
with teeth, chewing and mimic
muscles, mucosa of oral cavity,
tongue, soft palate, salivary
glands.
Normally chewing is an inborn reflex (!).

9.  It provides complex coordination of
conditioned and unconditioned digestive
motor reflexes that contribute to the time of
presence of food in oral cavity.
 It provides primary mechanical processing of
the food. The more the food is chewed the
more will be effective digestion of it in the
lower parts of digestive system.
 Chewing act influences on secretory functions
of digestive system (particularly on secretion of
gastric and pancreatic juices).

10.  Food irritates the receptors of oral cavity 
afferent impulses travel via trigeminal nerve (V
cranial), glosso-pharyngeal nerve (IX cranial),
superior laryngeal nerve (part of vagus) and
chorda tympani (part of facial nerve, VII cranial) 
impulses arrive to the sensory nuclei of medulla
oblongata (nucleus tractus solitarii, nucleus of
trigeminal nerve)  than information is travelling
to the cortex where it is being analysed (good or
bad food)  efferent fibers go via trigeminal, facial
and hypoglossus nerves to the chewing and mimic
muscles, that provide the chewing act.

11. Is a physiological reflex act during which the digestive bolus is
propelled from the oral cavity into the esophagus. Receptors for
this act are located in the root of tongue, soft palate and
posterior wall of pharynx.
Swallowing act consists of 3 phases:
 Oral phase – food is moistened by saliva, masticated and
moved to the posterior part of oral cavity (in general
voluntary phase).
 Pharyngeal phase – starts when digestive bolus comes behind
the palatinal arc. Complex process carried by IX and X
cranial nerves. Nasopharynx and larynx close and the bolus
moves into esophagus (unvoluntary).
 Esophageal phase – propelling of bolus via the tube of
esophagus (unvoluntary).

12. Though the beginning of swallowing is a voluntary
act, later it becomes involuntary and is carried out by
a reflex action called deglutition reflex. It occurs
during the pharyngeal and esophageal stages.
Stimulus
When the bolus enters the oropharyngeal region, the
receptors present in this region are stimulated.
Afferent Fibers
Afferent impulses from the oropharyngeal receptors
pass via the glossopharyngeal nerve fibers to the
deglutition center.

13. Center
Deglutition center is at the floor of the fourth ventricle in
medulla oblongata of brain.
Efferent Fibers
Impulses from deglutition center travel through
glossopharyngeal and vagus nerves (parasympathetic
motor fibers) and reach soft palate, pharynx and
esophagus. The glossopharyngeal nerve is concerned
with pharyngeal stage of swallowing. The vagus nerve
is concerned with esophageal stage.
Response
The reflex causes upward movement of soft palate, to
close nasopharynx and downward movement of
epiglotis, to close respiratory passage (larynx), so that
bolus enters the esophagus. Now the peristalsis occurs in
esophagus, pushing the bolus into stomach.

15. Various oral glands produce liquid that is called
saliva. It is essential for digestion (!)
Functions of saliva include:
 Significant role in providing of organism with the
information about properties of food. Reception of
food is possible only when food is moistened by saliva
(!).
 Providing initial chemical processing of the food by
enzymes in it.
 Taking part in the formation of digestive bolus.
 Protective function – contains immunoglobulin A,
lysosyme etc.
 Trophic action – supplies nutrients for teeth (ions of
Calcium, Phosphorus)
 Has a role in speaking.

16.  Salivary glands are divided into:
1) major; 2) minor (buccal, lingual)
There are 3 pairs of major salivary glands:
1) parotid; 2) submandibular;
3) sublingual.
Classification of salivary glands according to their
secretion:
1) Serose (protein) glands – produce liquid saliva without
mucine, but rich in enzymes (parotid glands).
2) Mucous glands – produce viscous saliva rich in mucous
(sublingual glands).
3) Mixed glands – combine the features of serose and
mucous glands (submandibular glands)

17. Normally humans produce up to 2 litres of saliva
per day (approximate rates are: 0.05 ml/min
during sleep, 0.5 ml/min at rest, 5 ml/min
maximally).
pH of saliva is 5,8-7,3.
The quantity of produced saliva depends from:
1) level of “food dryness”;
2) level of food fragmentation;
3) chemical composition of food.

19.  Regulation of salivation divided on nervous and
humoral. Nervous regulation is presented by
conditional and unconditional reflexes.

20.  Starts from irritation of receptors in oral cavity.
Afferent fibers go via lingual, glossopharyngeal
and vagus nerves to center of salivation which
is located in medulla oblongata. Efferent fibers
divided on sympathetic and parasympathetic.
Sympathetic fibers inhibit secretion of saliva
(small quantity of thick saliva).
Parasympathetic fibers (chorda tympani)
stimulate of secretion of saliva (high quantity
of watery saliva).

21.  Starts from irritation of receptors of vision,
hearing, and olfaction. Impulses go to specific
areas of cortex then to medulla oblongata.
Parasympathetic division of A.N.S.  secretion of watery
saliva lacking enzymes; sympathetic division of A.N.S. 
secretion of thick saliva rich in enzymes.
Humoral regulation (very small role): adrenalin (-),
thyroxine (-), acetylcholine (+), sex hormones (-).

22.  Is a depot (storage) for food.
 Providing further mechanical processing of food.
 Providing further chemical processing of food.
 Protective – gastric acidity (due to presence of
hydrochloric acid (HCl)) and lysozyme kill microbes
that come with food.
 It is involved in hemopoesis – gastric mucosa releases so
called intrinsic factor of Castle (gastromucoprotein),
that in organism combines with the vitamin B12
(extrinsic factor of Castle). Only in such combined state
vitamin B12 that is essential for hemopoesis could be
absorbed from the intestines into the organism.

23.  Chief cells – produce
pepsinogen that is an
inactive form of the
proteolytic enzyme pepsin
(located mainly in fundus
and body of stomach).
 Parietal cells – produce
HCl and intrinsic factor
(located mainly in fundus
and body of stomach).
Enterochomaffin - like cell
- produce histamine
(stimulates acid).

24.  Accessory cells – produce gastric mucus. It protects
gastric mucosa from digestive action of HCl acid
and gastric enzymes (almost totally located in
cardiac area of the stomach and also antral/pyloric
area).
 G-cells – endocrine cells that produce hormone
gastrin, which influences on motility and secretion
of gastrointestinal tract. In order to perform its
action gastrin should be firstly released into
bloodstream and then with blood it returns back to
GI tract and exert the action (located mostly in
antral and pyloric areas of stomach).
 D-cells-produce somatostatin (inhibits acid).

25. The fluid secreted by the gastric glands is called
gastric juice. Normally 1.5 – 2 litres of gastric juice
are produced per day. The quantity of produced
gastric juice depends from:
1) time elapsed since the intake of food;
2) chemical composition of food.
 Juice that is released during the state of fasting is
called basal gastric secretion (approximate rate is 5-
15 ml/h).
Composition of gastric juice:
 99.5 %  water; 0.5 %  organic and non-organic
waste (electrolytes + HCl).
 One of the most important non-organic compound
of gastric juice is hydrochloride acid (HCl).

26.  Catalyses the transformation of inactive pepsinogen
into active pepsin.
 Provides optimal pH for the action of enzymes,
particularly pepsin (normal pH range 1.5 – 2.5).
 Makes denaturation of proteins (they begin to lose
their structure) and it becomes more easier for pepsin
to break down proteins.
 Protective function – killing of microbes, that enter
stomach.
 Stimulates the production of pancreatic juice.
 Regulates motor function of pylorus. Low acidity
caused by the deficiency in HCl production violates
the normal passage of chyme (partially digested food
in stomach) from the stomach to duodenum as the
sphincter stays partially relaxed.

27. Proteolytic (Protein-degrading enzymes) - the major function is to
break down the proteins into smaller peptides:
a) Pepsin
b) Gastriksin
c) Parapepsin
c) Chymosin (babies to 1 year old have this enzyme)
 Amylolytic (starch-converting enzyme) – gastric amylase,
enzyme that digests carbohydrates (starch, glycogen) into
oligosaccharides (has low significance in stomach).
 Lipolytic - enzyme that digests lipids:
a) gastric lipase - is mostly important in lipid digestion of
infants (!) (triglycerides -----diglyceride);
b) gastric phospholipase.

28.  The digestive actions of the stomach reduce food
particles to a solution known as chyme, which contains
molecular fragments of proteins and polysaccharides
and droplets of fat.
Gastric mucus (mucine) lubricates stomach (0,5-1mm). This
called barrier of Cholendona.
The role of gastric mucus:
 Protective function from mechanical and chemical
damages;
 Neutralization of hydrochloric acid;
 Adsorption active enzymes;
 Provides absorption of vit. B12.

29. There are 3 phases of gastric secretion:
 Cephalic (up to 30% of total value)
 Gastric (60 %)
 Intestinal (10 %)

30. Cephalic phase of secretion starts
even before the food enters the
stomach. The main triggers of gastric
secretion in this phase are:
1) the look of food;
2) the smell of food;
3) the taste of food when it is already
being processed in the oral cavity.
Neurogenic signals that cause the
cephalic phase of gastric secretion
originate in the cerebral cortex and in
the appetite centres of the amygdala
and hypothalamus. Efferent impulses
from these centres go to stomach via
vagus nerve and cause secretion of
gastric juice.

31. Starts when food arrives to the stomach. The main triggers of
gastric secretion in this phase are:
1) distension (stretching of stomach wall);
2) chemical composition of food.
Stretching of stomach walls activates mechanoreceptors that leads to
release of acetylcholine (Ach) both via local secretion and via release
from vagus nerves.
Released Ach increases the secretion of gastric juice by:
1) direct stimulation of gastric mucosal glands;
2) stimulation of release of hormone gastrin from G-cells of gastric
mucosa.
Gastrin is a powerful stimulant of secretion of HCl
and also of gastric enzymes and mucus. Peptides and
amino acids have direct effect of stimulation of G-
cells to produce gastrin. Gastrin secretion is inhibited
when pH of gastric juice decreases (!).

32.  Intestinal phase starts when chyme enters to
duodenum. The main trigger of gastric secretion
in this phase is small amount of gastrin released
by the duodenal mucosa.
 Secretin - a hormone that is released by duodenal
mucosa has effect of suppression of gastric acid
secretion.

33. Parasympathetic nervous system
(vagus nerves) has strong
secretory influence on gastric
secretion.
Sympathetic nervous system
inhibits gastric secretion.

39.  Into duodenal lumen pancreatic juice, bile and
juice of duodenal glands are excreted.
 pH of duodenal juice 4-8 and quantity –
approximately 0,5 l.
 Pancreatic juice is produced by pancreas in
quantity 1,5-2 liters per day. pH of this juice is
8,0-8,5. Alkaline reaction is provided by
presence of high concentration of bicarbonates.
Role of alkaline reaction: neutralization of acid
chyme which is coming from stomach and
support of optimal pH for activity of pancreatic
enzymes.

41.  Proteolytic enzymes: trypsin, chymotrypsin,
carboxypeptidase, elastase, ribonuclease and
deoxyribonuclease. These enzymes are in an inactive
form. Their activation takes place in intestinal
lumen. Pancreas releases trypsinogen. Conversion of
trypsinogen to trypsin is provided by the enzyme
enterokinase that is produced by duodenal glands.
Then trypsin acts on the inactive precursors
(chymotrypsinogen, procarboxypeptidase, and
proelastase) to produce chymotrypsin,
carboxypeptidase, elastase. Proteolytic enzymes
digest proteins into dipeptides and oligopeptides.

42.  Amylolytic enzymes: pancreatic amylase.
Amylolytic enzymes digest carbohydrates into
monosaccharides.
 Lipolytic enzymes: pancreatic lipase,
phospholipase A. Lipolytic enzymes digest
emulsified lipids to monoglycerides and free
fatty acids.

43.  Distinguish 3 phases: cephalic (nervous), gastric
(nervous and humoral) and intestinal
(humoral).
 The cephalic phase is represented by
unconditioned and conditioned food reflexes.
The major efferent nerve is vagus nerve.
 Gastric phase is represented most of all by
humoral regulation.
The main hormon in this phase is gastrin which
increases pancreatic secretion.

44.  Intestinal phase is represented by secretin and
cholecystokinin. In response to acidic chyme (pH
lower than 4,0) enteroendocrine cells in the small
intestinal mucosa liberate secretin into the blood.
Functions of secretin: stimulates pancreatic (high
concentration of bicarbonate ions and lower level of
enzymes) and bile secretions and inhibits gastric
secretion (HCl).
 In response to fatty acids and amino acids
enteroendocrine cells in the small intestinal mucosa
liberate cholecystokinin into the blood. Functions of
cholecystokinin: stimulates pancreatic secretion rich in
enzymes and increase bile secretion and formation.

45.  Liver produces bile. Each day, hepatocytes
secrete 0,5-1 liter of bile. It has a pH 7,6-8,6.
 Mechanisms of bile secretion and formation:
- active production of
bile acids;
- filtration of water and
ions from blood to bile;
- reabsorption of water
from bile in gallbladder.

46. Bile is secreted by hepatocytes. The initial bile
contains large quantity of bile acids, bile pigments,
cholesterol, lecithin and fatty acids. From
hepatocytes, bile passes through small ducts and
hepatic ducts and reaches the common hepatic duct.
From common hepatic duct, bile is diverted either
directly into the intestine or into the gallbladder.
Sodium, bicarbonate and water are added to bile
when it passes through the ducts. These substances
are secreted by the epithelial cells of the ducts.
Addition of sodium, bicarbonate and water increases
the total quantity of it.

47. 97.6% of water and 2.4% of solids which
consists of bile acids, bile pigments
(bilirubin, biliverdin), cholesterol, mucine,
free fatty acids, vitamins A, E, D and K,
inorganic components.
Most of the bile from liver enters the
gallbladder, where it is stored. It is released
from gallbladder into the intestine
whenever it is required.

48. Indexes Duodenal
(А)
Bladder (В) Liver (С)
Color Light-yellow Duck-brown Gold-yellow
Volume, ml 15-20 30-60 Determined
of zone and
time
Density
g/сm3
1,008-1,012 1,028-1,032 1,008-1,012
рН 7,0-7,5 6,5-7,5 7,5-8,5
Bilirubin
mlmol/l
0,5-1,0 1,7-3,4 0,5-1,0
Bile acids
g/l
4-5 18-22 4-5
Cholesterol
mlmol/l
1,3-2,8 5,2-15,6 1,3-2,8

49.  increases action of pancreatic enzymes,
 takes part in digestive processes by
emulsification of fats,
 provides absorption of fatty acids and vitamins
A, D, E and K,
 increases motility of GIT,
 bactericidal and bacteriostatic actions.

50. Bile secretion is a continuous process, the amount is
less during fasting. It starts increasing after meals and
continues for three hours. Secretion of bile from liver
and release of bile from the gallbladder are
influenced by some chemical factors, which are
categorized into three groups:
1. Choleretics (іubstances which increase the secretion
of bile from liver).
2. Cholagogue (an agent which increases the release of
bile into the intestine by contracting of gallbladder).
3. Hydrocholeretic agents (a substance which causes
the secretion of bile from liver, with large amount of
water and less amount of solids).

51. Digestion in small intestine
In small intestine 3 processes take place:
 Final stage of mechanical processing
of food
 Final stage of chemical processing of
food – hydrolysis (break down of
nutrients)
 Absorption of products of hydrolysis
Function of small intestine
includes:
- Secretory function
- Protective (barrier)
- Motor function
- Absorptive function

52. These all mentioned
factors are due to:
 Chyme is more than 6 hr
in intestine
 Glands of small intestine
produces a lot of enzymes
 Mucous membrane of
small intestine makes very
large surface area for
digestion and absorption
 Intensive blood supply of
small intestine.

53.  Intestinal juice (SUCCUS ENTERICUS) consists of
two parts: liquid ( 99.5%) and solid (0.5%).
 Liquid part consists of water. Functions of
liquid part: moisten and lubricate chyme,
neutralize chyme (pH of intestinal juice is 7,2-
8,6).
 Solid part consists of mucus particles where
approximately 60-70% of enzymes are located
and ions.

54.  enterokinase - specific activator of pancreatic
trypsinogen
 proteases – digest proteins into amino acids
 lipases – digest emulsified lipids to finishing
products
 amylolytic enzymes – carbohydrates – digest
carbohydrates to monosaccharides.

55.  In small intestine distinguish two processes of
hydrolysis of nutrients:
1. luminal digestion – it is in a lumen of small
intestine (20-50% of nutrients);
2. surface (membranous) digestion is performed
on surface of mucus membrane of small
intestine (50-80%).

56. Secretion of succus entericus is regulated by both
nervous and hormonal mechanisms.
NERVOUS REGULATION
Stimulation of parasympathetic nerves causes vasodilatation and increases the
secretion of succus entericus. Stimulation of sympathetic nerves causes
vasoconstriction and decreases the secretion of succus entericus. But, the role
of these nerves in the regulation of intestinal secretion in physiological
conditions is uncertain.
However, the local nervous reflexes play an important role in increasing the
secretion of intestinal juice. When chyme enters the small intestine, the
mucosa is stimulated by tactile stimuli or irritation. It causes the development
of local nervous reflexes, which stimulate the glands of intestine.
HUMORAL REGULATION
When chyme enters the small intestine, intestinal mucosa secretes
enterocrinine, secretin and cholecystokinin, which promote the secretion of
succus entericus by stimulation the intestinal glands.

57. Functions of
large intestine:
 Major function is
depot of food
which contains in
this part of GIT
 absorption of water
and water-soluble
substances
 takes part in
formation of feces
 secretory function
(this juice contains
some enzymes and
has pH 8-9)

59. The large intestine houses over 700 species of bacteria
(microbes )that perform a variety of functions.
Role of large intestine microbes (90-95% are
anaerobes):
 protective (this normal flora protects organism
from pathogenic infection by production of IgE)
 production of vitamins K, B2, B6, B12 and other
 takes part in digestion of carbohydrates
 inactivation of digestive juices

60. Absorption is a process of transfer of substances
(nutrients) across the intestinal epithelium into
the blood and lymph. Absorption provides
organism by plastic and energetic materials. It
depends on the structure of mucus, level of
digestion of food and composition of nutrients.

61.  Most nutrients are not absorbed in an oral
cavity. Water, alcohol, medicaments (validol,
nitroglycerine) and poisons (cyanides) are
absorbed in the oral cavity.
 Some carbohydrates, water, medicaments and
alcohol are absorbed in the stomach.
 All nutrients (end products of disintegration of
proteins, carbohydrates and fats) are absorbed
in a small intestine.

62.  There are micro- and macromolecules
transport.
 Transport by phagocytosis and pinocytosis -
endocytosis. Endocytosis- intracellular
digestion.
 Some substances may be transported through
intercellular spaces - persorption. This
mechanism explains the falling into the
internal environment a small number of
proteins (antibodies, allergens, enzymes) other
substances (dyes) and bacteria.

63.  Passive transport: diffusion (for the gradient of
concentration), osmosis ( for osmotic gradient),
and filtration (for electrochemical gradient).
 Water, cations, anions, salts, fatty acids, water-
soluble, lipide-soluble vitamins , fructose and
folice acid are absorbed by passive transport
 Active transport (against to the gradient of
concentration, osmotic and electrochemical
gradients). By help of protein and energy. Active
transport need energy of ATP. Amino acids,
monosaccharides are absorbed by active transport.

64.  Motility of the oral cavity is presented by mastication and
swallowing.
 Motility of the stomach:
1. Receptive relaxation;
2. Peristaltic waves.
Motility of small intestine is presented by tonic contraction
(tension of smooth muscles), peristaltic contraction (provides
move of chyme) and rhythmic segmentation (provides mix of
chyme). Regulation of motility of small intestine is provided
by myogenic, nervous and hormonal mechanisms.
Myogenic regulation is provided by pace-makers. The 1st
pacemaker is located in the bile duct (ductus choledochus) in
the duodenum and provides motility of upper part of small
intestine. The 2-nd pace-maker is located in ileocecal corner
and provides motility of lower part of small intestine. The
nervous regulation is provided by metasympathetic nervous
system.