9. Physiology of digestion

Physiology of digestion.
Common characteristic of the mouth cavity digestion
 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,
 3. Chemical processing of food;
 4. Mechanical processing of food;
 5. Absorption of some substances.
 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. 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
 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. 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
 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
 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
 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
 Conditional reactions caused by appearance of food, it
smell and other stimulus, which are connect with food.
 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
Influence of vegetative nerves on secretor
activity of salivary glands
 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.
 Mediator of parasympathetic nerve system –
acetylcholine – stimulate M-cholinoreceptors of
baso-lateral 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 –
membrane, activated adenilatcyclase that form
cAMP. These reaction caused production of a
small quantity of saliva which have a big quantity
of organic substances.
Functions of stomach
 1. Digestive (mechanical treatment,
absorption, evacuation, secretion, depo);
 2. Excretor;
 3. Incretor.
Secretor activity of stomach
 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 – 0,81,5.
Composition of stomach juice and their properties
 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
 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
Parietal cell
Role of the hydrochloric acid in the
 1. To promote the swell of protein;
 2. To promote the change of pepsinogen in
 3. To make optimal conditions for actions of
 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
 Cephalic phase is caused by nervous system. It has
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
to 3,5
Production of common 10-35
HCl, mmol/L
Production of free HCl, 0-20
Debit of common HCl, to 1,5
Debit of free HCl, to 1
Phases of stomach secretion
 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
 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.
Role of pancreas in the digestive system
 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,
Composition and properties of
pancreatic juice
 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 enzymes
 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
 In pancreatic juice presents proteolytic enzymes –
elastases, nucleases etc. They hydrolyzed protein to
peptides and aminoacids.
Lipolytic and amylolytic
 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
 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
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
 The 3 phase caused by chyme contents. The main
is humoral factors (secretin, cholecystokininpancreasemin).
 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
 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
 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:
 bilirubin,
 bile acids,
 cholesterol,
 leukocytes,
 some epitheliocytes,
 cristalls of bilirubin,
 calcium.
The role of bile
1. Neutralize the stomach acid;
2. Inhibit the act of stomach proteases;
3. Increase the activity of pancreatic lipase;
4. Emulsificates the lipids by help of bile acids
 5. Bile acids help stabilizing of emulsion;
 6. Increase the absorption of fatty acids, carrotin,
vitamins K, D, E;
 7. Increase tone and motor function of intestines
(more duodenum and large intestine);
 8. Decrease the activity of intestine micro flora;
 9. Take place of enzymes fixation on the intestines
Composition and properties of intestine juice
 Composition of intestine juice:
 mucine, enzymes – peptidase, saccharase, maltase,
immunoglobulins; ions; leukocytes; epitheliocytes
(200 g per day).
 pH of intestine juice is 7,5-8,0; production per
day – near 1,8-2,5 L.
 Functions:
ending hydrolyses of all nutritive
substances; protective of mucus wall; support of
chyme in fluid condition; formed of base reaction
of intestine contents.
Increase secretion: parasympathetic nerves,
secretine, and glucagons.
Digestion in the large intestine
 Composition of intestine juice: mucus, epithelial
cells, and small quantity of enzymes (peptidase,
lipase, nuclease, phosphatase).
 Functions:
protective from mechanical,
 chemical irritations;
 formed of base reaction of intestine contents.
Role of the micro flora of large
 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.