Motor function of
gastrointestinal tract
Phases of swallowing act of digestive
lump
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There are 3 phases of swallowing: oral, pharyngeal,
esophageal. Oral phase – food passes from the mouth into the
pharynx through oropharyngeal isthmus. It is voluntary as well
as reflex. This is initiated when the bolus reaches a depression
in the middle of the tongue. The stimulation of the receptors
already described starts the swallowing reflex. Mastication and
respiration are stop. The pharyngeal phase – food is pushed
from the pharynx into the esophagus. Stage 1 and 2 are
completed normally in 1 second. The esophageal stage – food
reaching the upper end of the esophagus is passed into the
stomach. It takes about 10 seconds. The 2 and 3 stages are
pure reflex actions. Swallowing can be done as voluntary act,
but mostly it is a reflex action.
Regulation of swallowing act
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From the receptors of mucous membrane covering oral cavity
afferent impulses arise and travel via the fifth, ninth and tenth
cranial nerves through their various branches. Stimulation of
the superior laryngeal nerve alone can produce reflex
swallowing. Swallowing center is a group of neurons present
in the reticular formation of the medulla oblongata. It
influenced by the pre-central gyrus, amygdala, inferior frontal
gyrus and inferior colliculus also.
Efferent nerves – There are chiefly the hypoglossal (concerned
with 1 stage); glossopharyngeal (with 2 stage) and vagus (with
2 and 3 stages) nerves. The 5, 7 and 11 cranial nerves also
have some role in this process.
Peculiarities swallowing of liquid
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Concentration of tongue root muscles, bottom of oral
cavity and soft palatinum help to fluid swallowing.
Fluid enters to esophagus and after that go to the
down part by help of gravity force.
Speed of fluid passing of esophagus is more quickly
than peristalsis of esophagus. These process need
from 1 to 2 seconds. Fluid stop for a few part of
second in the down part of esophagus to the time of
peristalsis wave come. At these time they enter to
stomach.
Role of motor function of stomach in
digestive processes
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The motor function of the stomach is effect by
contraction of the smooth muscle fibers
forming its wall. Its purpose is to mix the
stomach contents and to force food out of the
stomach into the intestine. An important role in
regulation that passage of food is played by the
sphincters.
Types of peristaltic waves
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Two types of relatively short and recurring contractions of the muscles are
distinguished. The first is encountered after a meal, when acid gastric juice
is secreted. It is in fundal and caudal part of stomach. There are 3 types of
waves in fundal part of stomach (peristaltic waves – with low amplitude;
tonic-peristaltic – with higher duration and amplitude; tonic – which do not
pass). Also there are 3 types of waves in caudal part of stomach (with low
amplitude; higher amplitude and duration; series of big rythmic contraction
on the phone of tonic contraction). The second type of contraction appears
when food passes from the stomach into the intestine, i.e. during the socalled evacuation of the stomach, and also during the hunger contractions
of an empty stomach. There are 3 types of waves: short period of strong
contraction during more than 10 minutes which is change by prolong
period of rest (more than one hour); middle intensive contractions which
are present all time; lower contractions which are present all time.
Regulation of motor function
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Impulses via the vagus and sympathetic nerves are of the greatest
importance to this motor activity. The vagus nerve mainly stimulates
contraction (force and rate), the splanchnic nerve inhibit gastric movement.
Humoral influences and chemical stimulation of the mucous membrane
have a marked effect on gastric movement. The humoral agents that initiate
contractions of the smooth muscles of the stomach are gastrin, histamine,
choline, and potassium ions; enterogastrone, adrenaline and noradrenaline,
and calcium ions inhibit gastric movements.
The smooth muscles of the stomach possess automatism. The muscular
coat of the stomach contains many nerve cells forming Auerbach's plexus,
which apparently participates in coordination of the contractions of the
various groups of muscle fibers.
Passage of food from stomach to
duodenum
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The contractions of the gastric muscles force food from the
stomach into the duodenum. The food that moves is the
surface layer which passes along the lesser curvature until it
reaches the pylorus, then leaves the stomach through the
opening in the sphincter.
The rate at which food passes into the duodenum varies
according to its amount, composition, and cosistency and to
the amount of gastric juice secreted. Carbohydrates are
evacuated more rapidly than food rich in proteins and that
more rapidly than food rich in fats. Fluids pass into the
intestine almost immediately after entering the stomach.
Role of sphincters in evacuation of
food from stomach to duodenum
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The mechanism of gastric evacuation used to be attributed to the fact that
the pyloric sphincter, open in an empty stomach, periodically closes and
opens during digestion. Its opening is caused by stimulation of the mucous
membrane at the exit from the stomach by the HCl of gastric juice. Some
food then passes into the duodenum, and turns its contents from the normal
alkaline state to acid. The acid acts upon the duodenal mucosa, causing a
reflex contraction of the pyloric muscles (closure of the sphincter), so
arresting the passage of food from the stomach. Once the acid is neutralized
by excreted juices the intestinal contents again turn alkaline and the whole
process is repeated. Since alkalinity persists over a considerable interval, a
new portion of food leaves the stomach after the previous one has been
adequately treated. The closing of the pyloric also occurs when fats are
introduced into the duodenum.
Regulation of evacuations speed of
food from stomach to duodenum
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The following factors are of importance to the
passage of food into the intestine: 1) the consistency
of the gastric contents (the gastric contents enter the
intestine as soon as they acquire a fluid or semifluid
consistency); 2) their osmotic pressure (hypertonic
solutions inhibit evacuation and leave the stomach
only after they have been diluted by gastric juice to
an isotonic concentration); 3) how full the duodenum
is (distention of the duodenum also delays evacuation
and can even cause its temporary arrest). The
evacuation is controlled by the nervous system and
humoral factors.
Meaning of motor function of small
intestine in digestion process
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By help of the movements of the small
intestine part of chyme mixed with juice of
pancreas, bile and secretes of intestinal glands.
Characteristic of shortenings types
of small intestine
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Three types of intestinal movements are distinguished – rythmical
segmentation, pendular and peristaltic.
Rythmical segmentation is a cotraction of circular muscles on the distance
1-1,5 cm which are separated one from another on the distance 15-20 cm.
Pendular movement is contraction of small part of longitudinal muscles. By
help of that wall of intestine change according to chyme. That is why
chyme transmitted back and forward and mixing.
Peristalsis movement is a circular constriction forms above a bolus of food
owing to contraction of the circular muscles, while the lumen below the
bolus is dilated by contraction of the longitudinal muscles. As a result, the
intestinal contents move toward the widened part; then contraction of the
circular muscles spreads to this part which in turn is constricted, while the
segment lying below it is distended by contraction of the longitudinal
musculature
Regulation of motor function of
small intestine
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Regulation of small intestines movement may
be myogenic, nervous and humoral. There are
2 pacemakers in small intestines: in the
entrance place of bile and pancreatic ducts in
duodenum and in ileum. The anterior
hypothalamus stimulate motility, posterior –
inhibit motility. Stimulate motility
acethylcholine, inhibit – katecholamines,
serotonine, histamine, bradikinine.
Role of motor function of big
intestine in digestion process
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In large intestine chyme concentrated by help
of absorption of water. Electrolites, watersoluble vitamins also absorbed here. In large
intestine is formed fecus. Chyme is moving
through all digestive tract during 2-3 days.
More time it present in large intestine. 3-4 time
per day strong propulsive peristalsis wave
transport contents in caudal direction.
Regulation of motor function of big
intestine
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Plants, celulose, which are bad digested,
stimulate peristalsis. Parasympathetic nerves
stimulate, and sympathetic nerves inhibit
motor function of large intestine.