Digestive systemDigestive system

Salivary glandsSalivary glandsThere are three pairs of salivary glands; There are three pairs of salivary glands; Parotid ,submandibular & sublingual Parotid ,submandibular & sublingual glands .glands .

Saliva contain two types of secretions:Saliva contain two types of secretions:

1-serous secretion containing ptyalin 1-serous secretion containing ptyalin αα amylase which is an enzyme for digestion of amylase which is an enzyme for digestion of starch.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. Hormonal It is a nervous mechanism. Hormonal mechanism is not in action because it is mechanism is not in action because it is

slow.slow.

The nervous mechanism is classified intoThe nervous mechanism is classified into

Unconditioned reflex: it is inborn reflex, food Unconditioned reflex: it is inborn reflex, food in the mouth causes a reflex secretion of in the mouth causes a reflex secretion of saliva.saliva.

Conditioned reflex; The sight or smell of Conditioned reflex; The sight or smell of food is frequency an adequate stimulus of food is frequency an adequate stimulus of the initiation of salivary secretion. the initiation 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 partially Some drugs as mercury and iodides and leads are partially

excreted in salivaexcreted in saliva ,which is import ants in medico legal worksmedico legal works.

Simple stomach•The stomach is the most dilated part

in alimentary canal it is function is the digestion & reservoir of food

• The simple stomach consists The simple stomach consists of three partsof three parts, Fundus ,body and pylorus.

• The glands of the fundus The glands of the fundus and the body contain three and the body contain three types of cellstypes of cells

• 1- The parietal or oxyntic cells; they are responsible for HCL and intrinsic factor secretion.

• 2-The chief or peptic cell; they secrete gastric enzymes as pepsin and rennin.

• 3- The argentaffine cells; they secrete serotonin( 5 hydroxytryptamine)

• 4- The mucus cells; they secrete mucin

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

bicarbonate.

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

inactivated .•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

pepsin.• 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

gastric emptying.

•Control of gastric secretion • It is divided into three phases

•1 -Nervous phase•2 -gastric phase

•3 -intestinal phase

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

• Hormonal Hormonal : 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 stimulate gastric This types of stimulus independent of C.N.S can stimulate gastric

secretion ,from food extract ,liver extract vegetable secretion ,from food extract ,liver extract vegetable extract ,partially digested proteins ca and alcoholextract ,partially digested proteins ca and alcohol .

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 & duodenum.

• 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

gastric secretion.

• 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.

فيت السره العلميه اللجنه من إهداءيونايتد

Vet UniteD KfsWe Do The Best.... To Be The

Best