digestivecccccccccccccccc system lec.ppt

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

 Digestion is defined as the process by which food is broken down into simple chemical
substances that can be absorbed and used as nutrients by the body.
 A normal young adult consumes 1 kg of solid diet and 1–2 Liter of fluid per day.
 Functions of digestive system includes
 Ingestion or consumptions of food substances.
 Breaking them into small particles.
 Transport of small particles to different areas of the digestive tract.
 Secretion of necessary enzymes and other substances for digestion.
 Digestion of the food particles.
 Absorption of the digestive products.
 Removal of unwanted substances from the body.
 Maintaining of homeostasis.
Maintaining of homeostasis.


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.

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

 GI tract is a tubular structure extending from
the mouth up to anus, with a
 length of about 30 feet. It opens to the external
environment on both ends.
 GI tract is formed by two types of organs:
 1. Primary digestive organs.
 2. Accessory digestive organs

 Primary digestive organs are the organs where
actual digestion takes place. Primary digestive
organs are:
 i. Mouth
 ii. Pharynx
 iii. Esophagus
 iv. Stomach
 v. Small intestine
 vi. Large intestine

 Accessory digestive organs are those which help primary
digestive organs in the process of digestion.
 Accessory digestive organs are:
 i. Teeth
 ii. Tongue
 iii. Salivary glands
 iv. Exocrine part of pancreas
 v. Liver
 vi. Gallbladder

 The food is ingested via
The food is ingested via
mouth that is the initial part
mouth that is the initial part
of digestive system. The
of digestive system. The
mouth is divided into 2
mouth is divided into 2
regions,
regions, the vestibule
the vestibule
(region between the teeth,
(region between the teeth,
lips, and cheeks) and
lips, and cheeks) and the
the
oral cavity
oral cavity (inner area
(inner area
bounded by the teeth).
bounded by the teeth).
The oral part of digestive system has attitude to the
The oral part of digestive system has attitude to the
intake of food, analysing of its features, preparing of
intake of food, analysing of its features, preparing of
food for chemical digestion and propelling it to the
food for chemical digestion and propelling it to the
esophagus.
esophagus.

 Mouth
 Digestion actually begins in the mouth.
 Food enters in the mouth or oral cavity.
Tasting, Mechanical breakdown of food. , and
the tongue moves the pieces around so that
saliva can be mixed with them, this begins the
digestion.

 Structures in the mouth that helps digestion:
 Teeth-cut, tear, crush and grind food.
 Salivary glands- produce and secrete saliva into
oral cavity.
 Parotid (beneath the cheeks).
 Submaxillary (below the jaw bone).
 Sublingual(below the tongue).

digestivecccccccccccccccc system lec.ppt

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

 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
In the act of chewing such organs take part: upper and lower
jaws with teeth, chewing and mimic muscles, mucosa of oral
jaws with teeth, chewing and mimic muscles, mucosa of oral
cavity, tongue, soft palate, salivary glands. Normally chewing
cavity, tongue, soft palate, salivary glands. Normally chewing
is an unconditioned (inborn) reflex (!).
is an unconditioned (inborn) reflex (!).

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

 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.

 Oral phase – food is moistened
– food is moistened
by saliva, masticated and
by saliva, masticated and
moved to the posterior part of
moved to the posterior part of
oral cavity (in general
oral cavity (in general
voluntary phase).
voluntary phase).
 Pharyngeal phase – starts when
– starts when
digestive bolus comes behind
digestive bolus comes behind
the palatinal arc. Complex
the palatinal arc. Complex
process carried by IX and X
process carried by IX and X
cranial nerves. Nasopharynx,
cranial nerves. Nasopharynx,
oropharynx and larynx close
oropharynx and larynx close
and the bolus moves into
and the bolus moves into
esophagus (unvoluntary).
 Esophageal phase – propelling
– propelling
of bolus via the tube of
of bolus via the tube of

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.

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.

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

 Salivary glands are
Salivary glands are
divided into:
divided into:
1) major;
1) major;
2) minor (buccal,
2) minor (buccal,
lingual)
lingual)
 There are
There are 3 pairs of
3 pairs of
major salivary glands
major salivary glands:
:
1) parotid;
1) parotid;
2)
2)
submandibular;
submandibular;
3) sublingual.
3) sublingual.

Classification of salivary glands according to their
Classification of salivary glands according to their
secretion:
secretion:
1)Serose (protein) glands
1)Serose (protein) glands – produce liquid saliva
– produce liquid saliva
without mucin, but rich in enzymes (parotid
without mucin, but rich in enzymes (parotid
glands).
glands).
2)Mucous glands
2)Mucous glands – produce viscous saliva rich in
– produce viscous saliva rich in
mucous (sublingual glands).
mucous (sublingual glands).
3)Mixed glands
3)Mixed glands – combine the features of serose
– combine the features of serose
and mucous glands (submandibular glands)
and mucous glands (submandibular glands)

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

~99%
~99%
 water
water
~1 %
~1 % 
 organic and non-organic waste
organic and non-organic waste
Organic waste
Organic waste consists mostly of proteins and includes
consists mostly of proteins and includes
the enzyme salivary α-amylase. The major function of
the enzyme salivary α-amylase. The major function of
this enzyme is to break down the carbohydrates in
this enzyme is to break down the carbohydrates in
foods into oligosaccharides (dextrans, maltose). Also
foods into oligosaccharides (dextrans, maltose). Also
there is salivary lipase (breaks down fats, it is more
there is salivary lipase (breaks down fats, it is more
significant in newborns than in adults).
significant in newborns than in adults).
Mucin
Mucin moistens the food.
moistens the food.
Lysosyme
Lysosyme is a protective enzyme that kills bacteria.
is a protective enzyme that kills bacteria.
Non-organic waste
Non-organic waste
includes electolytes
includes electolytes.

 Hyporsalivation
Hyporsalivation
1) stress ( SNS),
1) stress ( SNS),
2) fluid loss,
2) fluid loss,
3) in the use of some drugs
3) in the use of some drugs
(sleeping medication),
(sleeping medication),
4) diabetes mellitus ,
4) diabetes mellitus ,
5) systemic diseases of
5) systemic diseases of
the Salivary glands.
the Salivary glands.
Hypersalivation
Hypersalivation
1) inflammation of the oral cavity,
1) inflammation of the oral cavity,
2)
2)
disorders of G.I.T.
disorders of G.I.T.

 FUNCTIONAL ANATOMY OF STOMACH
Stomach is a hollow organ situated just below
the diaphragm on the left side in the abdominal
cavity. Volume of empty stomach is 50 mL.
Under normal conditions, it can expand to
accommodate 1 L to 1.5 L of solids and liquids.
However, it is capable of expanding still
further up to 4 L.

 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.

 In humans, stomach has four parts:
1. Cardiac region
2. Fundus
3. Body or corpus
4. Pyloric region.

1. Cardiac Region
Cardiac region is the upper part of the stomach where
esophagus opens. The opening is guarded by a sphincter
called cardiac sphincter, which opens only towards
stomach. This portion is also known as cardiac end.
2. Fundus
Fundus is a small dome
shaped structure. It is elevated
above the level of esophageal opening.
3. Body or Corpus
Body is the largest part of stomach forming about 75% to
80% of the whole stomach. It extends from just below the
fundus up to the pyloric region

4. Pyloric Region
Pyloric region has two parts, antrum and pyloric canal.
The body of stomach ends in antrum. Junction between
body and antrum is marked by an angular notch called
incisura angularis. Antrum is continued as the narrow
canal, which is called pyloric canal or pyloric end. Pyloric
canal opens into first part of small intestine called
duodenum. The opening of pyloric canal is guarded by a
sphincter called pyloric sphincter. It opens towards
duodenum. Stomach has two curvatures. One on the right
side is lesser curvature and the other on left side is greater
curvature.

STRUCTURE OF STOMACH WALL
• Stomach wall is formed by four layers of structures:
1. Outer serous layer: Formed by peritoneum
• 2. Muscular layer: Made up of three layers of smooth muscle
fibers, namely inner oblique, middle circular and outer
longitudinal layers.
• 3. Submucus layer: Formed by areolar tissue, blood vessels,
lymph vessels and Meissner nerve plexus.
• 4. Inner mucus layer: Lined by mucus-
secreting columnar
epithelial cells. The gastric glands are situated in this layer. Under
resting conditions, the mucosa of the stomach is thrown into
many folds. These folds are called rugae. The rugae disappear
when the stomach is distended after meals. Throughout the
inner mucus layer, small depressions called gastric pits are
present. Glands of the stomach open into these pits. Inner
surface of mucus layer is covered by 2 mm thick mucus.

CLASSIFICATION OF GLANDS OF THE
STOMACH
• „ Gastric glands are classified into three types,
on the basis of their location in the stomach:
1. Fundic glands or main gastric glands or
oxyntic glands: Situated in body and fundus of
stomach
• 2. Pyloric glands: Present in the pyloric part of
the stomach
• 3. Cardiac glands: Located in the cardiac
region of the stomach.

„ STRUCTURE OF GASTRIC GLANDS
• 1. Fundic Glands
• Fundic glands are considered as the typical gastric glands (Fig.
38.2). These glands are long and tubular. Each gland has three
parts, viz. body, neck and isthmus.
• Cells of fundic glands
• 1. Chief cells or pepsinogen cells (release enzyme pepsinogen)
• 2. Parietal cells or oxyntic cells (Produce HCL)
• 3. Mucus neck cells
• 4. Enterochromaffin (EC) cells or Kulchitsky cells
• 5. Enterochromaffin
like (ECL) cells. Parietal cells are different from
other cells of the gland because of the presence of canaliculi
(singular = canaliculus). Parietal cells empty their secretions into
the lumen of the gland through the canaliculi. But, other cells
empty their secretions directly into lumen of the gland.

 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).

 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).

 Enterochomaffin-
like cell - produce
histamine
(stimulates acid) .
 D cells-
produce
somatostatin
(inhibits acid).

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).

 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.

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

 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 (mucin) 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.

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

 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.

Starts when food arrives to the stomach. The
main triggers of gastric secretion in this phase are:
1)
distension (stretching of stomach wall);
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 (!).

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

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