Transcript Lecture 27. Digestion in oral cavity and stomach

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Digestion in oral cavity and
stomach
Common characteristic of the mouth cavity digestion
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In the oral cavity take place such main processes:
1. Primary analyses of substances, which are
coming to organism – taste analyzes;
2. Reflector signals from receptor, which are
present in these area to the another organs of
digestive system, to the central nerve system –
medulla oblongata, stomach, small intestine,
pancreas;
3. Chemical processing of food;
4. Mechanical processing of food;
5. Absorption of some substances.
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Chewing of food is important, because
fruits and vegetables have cellulose
which must be broken before the food
can be utilized. In the mouth cavity
begin digestion of carbohydrates, which
help to the functional activity of
pancreas.
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When our food are in the mouth stimulate the
receptors of oral cavity; from which impulses
go to the different part of brain and return to
different part of digestion tract – stomach,
small intestine, pancreas, in which secreted
juices with enzymes
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In the mouth cavity open three pair of big
salivary glands and a lot of small buccal
glands. Submandibular and sublingual
glands consist of the cells of serum and
mucous types and secrete serous and mucus
types of saliva. Parotid glands consist of the
serum types cells and secrete serous type of
saliva.
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Small buccal glands consist of mucous types
of cells; produce mucous saliva with a big
quantity of water. Saliva necessary for our
digestion. In a mouth chewing a food by teeth
and lingual. In the mouth cavity begin
digestion of carbohydrates by alfa-amilase –
ptyalin. To secrete different types of saliva for
digestion processes – with a big quantity of
water or organic and inorganic substances.
Quantity, composition and properties of
saliva
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Quantity, composition and properties of saliva (In the
case of dream produce nearly 0,05 mL/minute, in the
normal condition – 0,5 mL/minute, in the case of
maximal secretion – near 5 mL/minute. By day
produce 0,8-1,5 L of saliva. Composition of saliva:
water, organic – alfa-amilase, lipase, phosphatase,
RNAase, DNAase, mucin, substances for protective –
lisocim, thiocianates, antibodies – and unorganic
substances – sodium, potassium, calcium, chlorites,
etc.
Mechanism of saliva forming
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In acinars' cells produce primary saliva in which
synthesis necessary amino acids, glucose, mineral
substances (for example, Ca++). In the cells of
salivary glands occur passive processes, which
provide moving of water and electrolits from blood to
the glands’ ductus (strait). In the ductus occur
reabsorption of sodium, chlorine, secretion of
potassium, HCO3–. This is the secondary saliva.
Aldosterone increase reabsorption of sodium and
secretion of potassium.
Role of saliva in vitality of human
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1. Moisten of solid food;
2. Dissolving of substances;
3. Moisten of mouth;
4. Cover food;
5. To help of swallowing;
6. Primary hydrolyzing of carbohydrates;
7. Antibacterial properties;
8. Neutralized the stomach juice.
Formation of saliva
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Conditional reactions caused by appearance
of food, it smell and other stimulus, which
are connect with food.
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Unconditional influences have parasympathetic and
sympathetic components. Parasympathetic
components beginning from receptors of tongue
and oral cavity. From its impulses pass through the
fibers of n. trigeminus, n. facialis, n. vagus, n.
glossopharyngeus, to the center of salivation.
Impulses return to saliva glands by n. facialis, n.
glossopharyngeus. Sympathetic components of
unconditional influences beginning from side cornu
of upper thoracic segments of spinal cord – Th2-Th4. Then impulses go to saliva glands through the
upper cervix sympathetic ganglion. The cortex of
big hemispheres, hypothalamus, lymbic system
regulate the salivation through these nerves.
Conditional signals, emotions may inhibit
salivation.
Influence of vegetative nerves on secretor
activity of salivary glands
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Stimulation of the parasympathetic nerve
supply causes profuse secretion of watery
saliva with a relatively low content of
organic material. Stimulation of the
sympathetic nerve supply causes profuse
secretion of saliva with small quantity of
water with a relatively big content of
organic material.
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Mediator of parasympathetic nerve system –
acetylcholine – stimulate M-cholinoreceptors of basolateral membrane and activate entrance of Ca2+ and
activate kalmodulin. These reaction caused
production of a big quantity of saliva with low
quantity of organic substances. Mediator of
sympathetic nerve system – norepinephrine –
stimulate adrenoreceptors of basolateral membrane,
activated adenilatcyclase that form cAMP. These
reaction caused production of a small quantity of
saliva which have a big quantity of organic
substances.
Swalowing
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.