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Digestion in the stomach.
Functions of stomach
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1. Digestive (mechanical treatment,
absorption, evacuation, secretion, depo);
2. Excretor;
3. Incretor.
Secretor activity of stomach
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Production of stomach juice per day – near 2,5
L of juice. Their main components – enzymes,
HCl and mucin. pH of morning saliva is
neutral, after eating – sour – 0,8-1,5.
Composition of stomach juice and their properties
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There are 2 types of glands – the oxyntic (or
gastric) and the pyloric glands. The oxyntic glands
secrete hydrochloric acid, pepsinogen, intrinsic
factor, and mucus. The pyloric glands secrete
mainly mucus. The main cells (peptic or chief
cells) produce non active enzymes (pepsinogens).
There are 7 pepsinogens. They hydrolyzed
proteins.
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Optimum pH of its activity is 1,5-2,0. Pepsinogens
whose activity the most in the condition of pH 3,23,5 is gastrecsin. In the stomach juice produces
lipase and gelatinese. HCl produce in parietal or
oxyntic cells. pH of it secrete is near 0,8. These
processes need energy of lipids. Mechanism of it
production: Cl- activly transported in the
canaliculi, Na+ – from the canal into cytoplasm.
H2O dissopciated to H+ and OH-. H+ activly go
into canaliculi in change of K+. In these processes
take plase Na+,K+-ATPase. CO2, which produce in
cells act with H+ and syntheses HCO-. This anion
go into the cell in change by Cl-.
Formation of hydrochloric acid
stomach
Parietal cell
blood
metabolism
carboanhydrase
se
Role of the hydrochloric acid in the
digestion
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1. To promote the swell of protein;
2. To promote the change of pepsinogen in
pepsins;
3. To make optimal conditions for actions of
pepsins;
4. To fulfill protective role from bacteria;
5. To promote motor and evacuated
functions of stomach;
6. To stimulate production of duodinum
gormon – secretin.
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 of common 10-35
HCl, mmol/L
40-60
80-100
3.
Production of free HCl, 0-20
mmol/L
20-40
65-85
4.
Debit of common HCl, to 1,5
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.