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Digestive systemDigestive system
Salivary glandsSalivary glands
There are three pairs of salivary glands;There are three pairs of salivary glands;
Parotid ,submandibular & sublingual glands .Parotid ,submandibular & sublingual glands .
Saliva contain two types of secretions:Saliva contain two types of secretions:
1-serous secretion containing ptyalin1-serous secretion containing ptyalin αα
amylase which is an enzyme foramylase which is an enzyme for
digestion of starch.digestion of starch.
2- mucus secretion for lubricating purpose.2- mucus secretion for lubricating purpose.
Mechanism of salivary secretionMechanism of salivary secretion
It is a nervous mechanism. HormonalIt is a nervous mechanism. Hormonal
mechanism is not in action because it ismechanism is not in action because it is
The nervous mechanism is classified intoThe nervous mechanism is classified into
Unconditioned reflex: it is inborn reflex, foodUnconditioned reflex: it is inborn reflex, food
in the mouth causes a reflex secretion ofin the mouth causes a reflex secretion of
Conditioned reflex; The sight or smell of foodConditioned reflex; The sight or smell of food
is frequency an adequate stimulus of theis frequency an adequate stimulus of the
initiation of salivary secretioninitiation of salivary secretion..
Composition and volume of saliva
• It contain small amount of inorganic ions ,proteins and in some species ptyalin or α
amylase for digestion of starch.
• The secretion of parotid glands of ruminants tend to be slightly alkaline .
• Bicarbonate & phosphate are the two principle anions and its very import ants to
the buffering capacity of the plasma.
Functions of salivaFunctions of saliva
• Saliva has a lubricating actionSaliva has a lubricating action which facilitate the mastication and
deglutition of ingested food.
• The mucin in salivaThe mucin in saliva assists the formation of food boluses of a convenient
size for swallowing.
• Saliva contain factor that actually destroyed bacteria ,one of these factor is
thiocyanide and several proteolytic enzyme (lyzsosomes) that attack bacteria ,enter
bacteria & become bacteriosidal.saliva contain significant amount of protein
antibody that can destroy oral bacteria which cause dental cariesantibody that can destroy oral bacteria which cause dental caries.
• Regulation of body temperature in panting animals:Regulation of body temperature in panting animals: by
evaporation of saliva
• Regulation of water balance ;Regulation of water balance ;
Dehydration leads to decrease salivation this leads to dryness of mouth & pharynx
,which stimulate thirst sensation
• Buffering actionBuffering action; oral Ph at 7 at this Ph saliva is saturated with calcium ,so
the teeth don’t lose calcium to oral fluids.
• Some drugs as mercury and iodides and leads are partiallySome drugs as mercury and iodides and leads are partially
excreted in salivaexcreted in saliva ,which is import ants in medico legal worksmedico legal works.
•The stomach is the most dilated part
in alimentary canal it is function is
the digestion & reservoir of food
• The simple stomachThe simple stomach
consists of three partsconsists of three parts,
Fundus ,body and pylorus.
• The glands of the fundusThe glands of the fundus
and the body containand the body contain
three types of cellsthree types of cells
• 1- The parietal or oxyntic cells; they
are responsible for HCL and intrinsic
• 2-The chief or peptic cell; they
secrete gastric enzymes as pepsin
• 3- The argentaffine cells; they
secrete serotonin( 5
• 4- The mucus cells; they secrete
Composition of gastric juice:
• Water and solids 99.5% and total solids 0.5%.
• Organic enzyme (pepsinogen –Rennin and gastric lipase.), on
enzyme (Hcl, mucin and intrinsic factor) .
• Inorganic cationsInorganic cations ,na k calcium anions phosphate and
Functions of gastric juiceFunctions of gastric juice;;
• PepsinPepsin: it is formed inside peptic cell in the form of pepsinogen.
• Pepsinogen by the action of Hcl is converted into pepsin
• Pepsin is an active proteolytic enzyme optimum ph is
• Above ph 5 it has a little proteolytic and become completely
•Pepsin is a milk clotting enzyme in human infants its function
is to keep milk for long time in stomach .hcl kill micro
organism in milk.
• Intrinsic factor (IF)Intrinsic factor (IF)
• It is secreted by the parietal cells. it binds with vit B 12 and helps
its absorption in the lower part of ileum.
• A lack of IF results in pernicious anemia
Function Of gastric HCL
• 1-Convertion of pepsinogen to pepsin.
• 2- Provides optimum PH for the action of pepsin.
• 3- It denaturant dietary proteins
• 4- Curdling of milk, so milk is exposed for long time to
• 5- Kill bacteria ( Antibacterial action)
• 6- It help calcium and iron absorption
• 7- It stimulate release of secretin hormone
• 8- It initiate enterogastric reflex, which regulate
•Control of gastric secretion
• It is divided into three phases
1-Nervous phaseNervous phase
• Conditioned reflex;Conditioned reflex;
Due to sight, smell, thought of food, such conditioned reflexes have their centers in the cerebral
cortex, or appetite centers of the hypothalamus.
• Unconditioned reflexUnconditioned reflex: It is produced from the presence of food in the mouth,
which stimulate taste buds. leads to afferent impulse from tongue,buccal cavity to vagal centre
with reflex gastric secretion through vagus nerve .
22--Gastric phase it includesGastric phase it includes;;
A-Central reflex( Extrinsic)A-Central reflex( Extrinsic)
• B-Local nerve plexuses intrinsic)B-Local nerve plexuses intrinsic)
Hormonal phase.Hormonal phase.
1- Central reflex (Extrinsic)
Stimulation of mechano,chemoreceptor of gastric mucosa by food leads to afferent impulse
through vagus nerve stimulate gastric secretion from oxyntic cell.
• 2-Local nerve plexuses (Intrinsic)2-Local nerve plexuses (Intrinsic)
• Stimulation of receptors of gastric mucosa by food lead to impulse in local neuron present in
sub mucosa( forming meissner reflex which leads to stimulation of secretion from oxyntic cell
• HormonalHormonal : Stimulation of the receptor of gastric mucosa by food leads to impulse through
local axon reflex to G Cell gastrin releasing cell in pyloric antrum which pass through portal
veins to the liver then through systemic circulation to the heaart return to the stomach through
its arterial supply to stimulate oxyntic& peptic cell which secret HCL
• Chemical stimulation (secretagogues)Chemical stimulation (secretagogues)
• This types of stimulus independent of C.N.S can stimulateThis types of stimulus independent of C.N.S can stimulate
gastric secretion ,from food extract ,liver extractgastric secretion ,from food extract ,liver extract
vegetable extract ,partially digested proteins ca andvegetable extract ,partially digested proteins ca and
3-Intestinal phaseIntestinal phase::
• Has a minimal role of gastric secretion
• Arrival of the food to the duodenum leads to increased gastric secretion by
stimulation of the local axon reflex which is continue between stomach &
• Released of intestinal gastrin from the duodenum which circulate to blood
& reach stomach to increase gastric secretion.
•Inhibition of gastric scretionInhibition of gastric scretion;;
• 1-Negative feedback from the stomach1-Negative feedback from the stomach
1- Acidified chyme in pyloric antrum ,gastric secretion is inhibited by low ph
,if gastric secretion drop to Ph 1.5 or more gasrtin secretion is stop .
2- D CELL located close to C Cell ,which secrete somatostatin which inhibit
• 2- Negative feedback from the duodenum:Negative feedback from the duodenum:
• Low ph (acid chyme)
• Enterogastrone hormone which include;
• Secretine hormone ; it is released from duodenal mucosa in
response to acid chyme .
• Cholystokinin –Pancriozymine ;It is released from the duodenal
mucosa in response to fatty acids, peptides and amino acids
• Gastric inhibitory peptide ; It is released from the duodenal
mucosa in response to fats and carbohydrates.
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