GENERAL CHARACTERISTICS
OF DIGESTIVE SYSTEM.
FEEDING OF BEHAVIOR
Components of the Digestive System
Gastrointestinal tract (GI) is
a continuous tube that
consists of the mouth,
pharynx, esophagus, stomach,
small intestine, large intestine,
and anus.
The lumen of this tube is
continuous with the external
environment.
The accessory organs are
the salivary glands, exocrine
glands, and biliary system
(liver and gallbladder).
Food Processing
Feeding behavior
Lack of food
Reduction of level
of nutrients
Excitation
chemoreceptors of
vessels
Feeling of hunger
(preventive motivation)
Lateral nucleus of the
hypothalamus
(hunger center)
Stimulates appetite
Find food (food reaction)
Saturation
 Sensory
Stretch
receptors of the
stomach
Ventromedial
hypothalamic nuclei
(center of saturation)
Lateral nuclei of
hypothalamus
(hunger center)
Ventromedial
hypothalamic nuclei
(center of saturation)
Lateral nuclei of
hypothalamus
(hunger center)
 Metabolic
Chemoreceptors
of vessels
“The feeding center”
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Hunger Center - lateral nuclei of the hypothalamus;
Center saturation - ventromedial nuclei of the
hypothalamus;
Brain stem centers that provide chewing, swallowing,
salivation, the allocation of digestive juices, motility;
Vegetative centers of the spinal cord (lateral horns of
segments T1-T4);
Limbic system (regulates emotions impact on hunger and
satiety, anger, rage - stimulate hunger, longing, sadness inhibit hunger);
Cerebral cоrtех are regulates behavioral responses meet
of nutritional dominant.
Functions of the digestive system
 Primary:
1. MOTILITY. This refers to the movement of
food through the digestive tract through the
processes of
 Ingestion: taking food into the mouth
 Mastication: chewing the food and mixing it
with saliva
 Deglutition: swallowing food
 Peristalsis: rhythmic, wavelike contractions
that move food through the gastrointestinal tract
Functions of the digestive system
2. SECRETION. This includes both exocrine and
endocrine secretions.

Exocrine secretions: Water, hydrochloric acid,
bicarbonate, and many digestive enzymes are
secreted into the lumen of the GI tract. The stomach
alone, for example, secretes 2 to 3 liters of gastric
juice a day.

Endocrine secretions: The stomach and small
intestine secretes a number of hormones that helps to
regulate the digestive system.
Functions of the digestive system
3. Digestion. This refers to the breakdown of
food molecules into their smaller subunits,
which can be absorbed.
4. Absorption. This refers to the passage of
digested end products into the blood or lymph.
5. Storage and elimination. This refers to the
temporary storage and subsequent elimination
of indigestible food molecules.
Functions of the digestive system
 Secondary
 Homeostatic. Gastrointestinal tract is involved
in maintaining the sustainability of water, the
concentrations of ions, glucose, amino acids,
fatty acids and others.
 Excretory
– expelling certain products of
metabolism (e.g. bile pigments), and the salt of
heavy metals, from organism.
 Hemodynamic. venous plexus of the
abdominal cavity is played role as depot of
blood.
Functions of the digestive system
 Regulatory. GIT is secreted by a numbers of
gastrointestinal hormones (GIH) that are
participating in the secretory, motor and suction
functions of the alimentary canal;
 Protective. Nonspecific protection is provided
by the bactericidal properties of saliva, gastric
juice, bile, and antitoxic barrier function of the
liver, vomiting. Specific protection is provided in
immunoglobulins, which are part of the digestive
secrets.
Digestion
Digestion: is the process of breaking down food
into molecules the body can use, the absorption of
nutrients, & the elimination of waste.
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Carbohydrates are broken down to monosaccharides
(example: glucose)
Proteins are broken down to amino acids
Lipids are broken down to fatty acids and glycerol
Types of digestion:
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Mechanical digestion: breaking chunks of food into
smaller pieces
Chemical digestion: changing food into the subunits
listed above by the action of enzymes
Types of digestion
 Classification
by localization
DIGESTION
INTRACELLULAR
EXTRACELLULAR
Contact
Pariental
Distal (cavity digestion)
Membrane
Types of Nutrients
 Micronutrients-
vitamins, minerals, & water
 Macronutrients-
proteins, lipids,
carbohydrates, etc…
The wall of the digestive tract consists of
four layers.
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The mucosa lines the luminal surface.
Its inner epithelial layer has exocrine
and endocrine cells. The lamina
propria is a middle layer of connective
tissue. The muscularis mucosa is a
sparse layer of smooth muscle.
The submucosa is under the mucosa
This connective tissue has large blood
and lymph vessels. It contains a
submucous plexus.
The muscularis externa is the main
smooth layer of the digestive tube. It is
between the submucosa and outer
serosa. The muscularis externa has an
inner circular layer and an outer
longitudinal layer. Their contractions
produce the propulsive and mixing
movements.
A myenteric plexus is between the two
smooth muscle layers.
Autonomous smooth muscle function
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Smooth muscle in GIT shows rhythmic
spontaneous variation in it’s resting
membrane potential (slow waves). It is also
called basic electric rhythm (BER). They do
not cause contraction by themselves, but
they bring smooth muscle to their thershold
and action potentials occur and at that time
contraction developed.
*** Smooth muscle cells is connected to the
adjacent smooth muscle cells by cap
junction and electrical activity in one muscle
can pass through these cap junction so the
whole muscle sheet acts as functional
syncytium.
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This slow cyclic electrical activity is
originated from pacemaker cell called Cajal
cells which found between circular and
longitudinal layers.
BER
Characteristic of mechanisms
regulation digestion
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Central nervous mechanisms
Inconditioned reflexes
(inborn)
Established when food
put in mouth
provide such complex reflex acts
as chewing, swallowing,
vomiting, and regulation of
secretion of saliva and gastric
and others. juice
Conditioned reflexes
(depend on experience)
Established by smell, by thought food,
by talking about food, and even by
sounds by its preparation
ensure the preparation of the
digestive system to eat foods
 Central nervous mechanisms especially pronounced in the upper part of
the alimentary canal, as distance from which their role is reduced.
Central Humoral Mechanisms
 almost
no effect on secretion and motility
GI tract, but have some effect on the
absorption of certain substances (calcium,
phosphorus, sodium, etc.)..
Methods of studying the functions of
the alimentary tract
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Experimental methods:
Fistula method;
X-raying method;
Clinical methods:
- Method for collecting human saliva by means of the
Lashley-Krasnogorsky capsule (small metal funnel);
- Electrogastrography;
- Х-raying methods;
- Endoscopy.