Download 37 Motor function of digestion

Motor function of
digestion
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.
Swallowing
Pharyngeal phase
Oral phase
Esophageal phase
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 so-called 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.
Phases of stomach secretion
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Cephalic phase is caused by nervous system. It has conditional and unconditional reflexes.
Conditional reactions caused by appearance of food, it smell and other stimulus, which are
connect with food. Unconditional influences is parasympathetic and beginning from
receptors of tongue and other receptors of the oral cavity. From these receptors impulses
pass through the fibers of n. trigeminus, n. facialis, n. glossopharyngeus, n. vagus to the
medulla oblongata. Impulses return to stomach by n. vagus. Except neuron influences this
phase has humoral influences – brunch of n. vagus produce gormon gastrin. These phase is
very short.
Value of gastric juice secretion
In norm gastric juice secretion must be
N
N
Indexes
Empty
stomach
Basal
secretion
Stimulated
secretion
1.
pH
to 3,5
1,5-2
1,3-1,4
2.
Production
common
mmol/L
of 10-35
HCl,
40-60
80-100
3.
Production of free 0-20
HCl, mmol/L
20-40
65-85
4.
Debit of common to 1,5
HCl, mmol/hour
1,5-5,5
8-14
5.
Debit of free HCl, to 1
mmol/hour
1-4
6,5-12
Phases of stomach secretion
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Stomach phase is depends on the quantity of food,
which are present in stomach. It has vago-vagal
reflexes (by mean of central nerves system) and
local – peripheral reflexes, which are closed in
stomach walls. Duration of these phase is longer
and quantity of juice is much. It has humoral
mechanisms too (production of gastrin and
histamin.
Intestine phase: presence of food in the upper
portion of small intestine can cause the stomach to
secrete small amount of gastric juice. This
probably results of gastrin are also released by the
duodenal mucosa in response to distension or
chemical stimuli of the same type as those that
stimulate the stomach gastrin mechanism.
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
Segmentation
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, water-soluble 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.
Role of the micro flora of large intestine
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1. Ending decompose of all nutritive substances, which are do not digested
in small intestines.
2. Synthesis of some vitamins – of B group, vitamin K.
3. Take place in metabolic processes.
4. Stimulates absorption of water and amino acids.
5. Inactivate enzymes of small intestines.
6. Forms normal reaction in large intestine.
7. Decompose organic substances of chyme.
8. Have protective role to the pathogenic microorganisms.
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.
Role of pancreas in the digestive system
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There are two secretor functions of pancreas – external and
internal. The external secretor function of pancreas means
that exsogenic cells of pancreas and ducts cells produce
pancreatic juice. It helps to hydrolyzed protein to peptides
and amino acids, carbohydrates to monosaccharides, lipids
to the fat acids and glycerin. It neutralizes acidic chymus,
which come from stomach.
Internal secretor function of pancreas is production of
hormones (insulin, glucagons, somatostatin).
Composition and properties of
pancreatic juice
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Quantity of pancreatic juice per day is 1,5-2,0 L.
Reaction of it – pH = 8,0-8,5. It consists of a big
quantity of hydro carbonates. It has near 10 % of
protein – enzymes, which are act on protein, lipids
and carbohydrates. According to that there are 3
groups of enzymes:
proteolytic
lipolytic
amilolytic
Proteolytic enzymes
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Proteolytic enzymes secreted in the inactive enzymatically
form. The more important of them are trypsinogen,
chymotrypsinogen, and procarboxypolypeptidase.
Trypsinogen activated by enzymes enterokinase (produces
by the mucous cells of duodenum).
After activation tripsinogen has name – tripsin. This
enzyme is very active. It also activates chemotripsinogen
to form chemotripsin, and procarboxypolypeptidase is
activated to the form carboxypolypeptidase in a similar
manner.
In pancreatic juice presents proteolytic enzymes –
elastases, nucleases etc. They hydrolyzed protein to
peptides and aminoacids.
Lipolytic and amylolytic enzymes
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The main enzymes for fat digestion (lipolytic enzymes) are
pancreatic lipase, which is capable of hydrolyzing neutral fat
into fatty acids and monoglycerides; cholesterol esterase,
which causes hydrolysis of cholesterol esters; and
phospholipase, which splits fatty acids from phospholipids.
Lipolytic enzymes ejected in active (pancreatic lipase,
muntinase) and inactive conditions (prophospholipase A).
The pancreatic digestive enzyme for carbohydrates (amilolytic
enzyme) is alpha-amylase, which hydrolyzes starches,
glykogen, and most other carbohydrates (except cellulose) to
form disaccharides and a few trisaccharides.
Regulation of pancreas secretion
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There are 3 phases of pancreatic secretion:
cephalic, stomach and intestine.
The 1 stage caused by nervous influences. N.
vagus realizes this effect by helps of conditioned
and unconditioned reflexes. Secretion begins after
1-2 minutes of food. Juice consists of enzymes,
small quantity of water and ions. Sympathetic
influences have a trophy role.
During the 2 phase there are two kinds of
influences: nervous and humoral (gastrin from
stomach).
The 3 phase caused by chyme contents. The main
is humoral factors (secretin, cholecystokininpancreasemin).
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Secretin stimulates production of a big quantity of
juice with a high concentration of hydrocarbonates
and a small quantity of enzymes in ducts cells.
CKP stimulates production of a less quantity of
juice with a big concentration of enzymes in
acinars cells.
Secretion of pancreatic juice stimulates also by
vaso-intestinal polypeptide, serotonine, insulin,
bombesin, sustantio P calcium ions, and salts of
bile acids.
Secretion of pancreatic juice inhibits by glukagon,
calcitonin, somatostatin. During dreams, hart
physical and mental activity, pain secretion
inhibits too.
Bile production and bile secretoin
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Secretion of bile occur all time and increase by
influences
of
bile
acids,
cholecystokininpancreasemin, secretin.
Bile secretion in the duodenum depends from take
food (minerals water, HCl, fatty acids increase bile
formation).
It depends of nervus vagus (increase bile formation)
and humoral influences – concentration of
cholecystokinin-pancreasemin
(increase
bile
formation and ejection), secretin, gastrin.
Composition of bile:
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bilirubin,
bile acids,
cholesterol,
leukocytes,
some epitheliocytes,
cristalls of bilirubin,
calcium.