Motor function of gastrointestinal tract

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Motor function of gastrointestinal tract
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Phases of swallowing act of digestive lump

• 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.

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Regulation of swallowing act

• 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.

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Peculiarities swallowing of liquid

• 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.

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Role of motor function of stomach in digestive
processes

• 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.

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Types of peristaltic waves

• 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.

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Regulation of motor function

• 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.

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Passage of food from stomach to duodenum

• 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.

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Role of sphincters in evacuation of food from
stomach to duodenum

• 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.

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Regulation of evacuations speed of food from
stomach to duodenum

• 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.

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Meaning of motor function of small intestine in
digestion process

• By help of the movements of the small intestine
  part of chyme mixed with juice of pancreas, bile
  and secretes of intestinal glands.

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Characteristic of shortenings types of small
intestine

• 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

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Regulation of motor function of small intestine

• 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.

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Role of motor function of big intestine in
digestion process

• 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.

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Regulation of motor function of big intestine

• Plants, celulose, which are bad digested,
  stimulate peristalsis. Parasympathetic nerves
  stimulate, and sympathetic nerves inhibit motor
  function of large intestine.

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