Transcript Phases of salivary secretion

Secretion of saliva:
The principle glands of salivations are parotid ,
submandibular & sublingual with many buccal
glands , the daily secretion of saliva is about 8001500 millilitters.
Saliva contain 2 types of secretion:
1- serous secretion contain a-amylase
2- mucous secretion
Pariatal glands secrete entirely serous secretion
,submandibular &sublingual secret both serous
&mucous , buccal gland mainly mucous .
PH os salivais about 6&7.
99.5% of saliva is water , 0.5%are solutes,
among them are salts of CL, Hco3,
phosphate of Na&k, some disolving gases,
vareous organic substances ,including urea ,
uric acid , albumin , globulin,
mucin,,bacteriolytic enzyme.
Water provide a medium for dissolving food ,
Cl activate salivary amylase , HCO3 &Ph
buffer chemicals , urea & uric acid help the
body to get rid of waste , mucous lubricate
the food so it can be easily turned in the
mouth & swallowed , lysozyme distroy
bacteria , so protect mucous memnbrane
from infection& teeth from decay.
Saliva prevent the harmful effect of bacteria by
:1- continuous washing away pathogenic
bacteria as well as food particles that provide
bacteria with metabolic support.
2- saliva contain many facter that can kill
bacteria such as proteolytic enzyme
Regulation of salivary secretion :
The superior & inferior salivary nuclei located
in the brain stem , control secretion by
salivary glands , these nuclei interne are
controlled mainly by taste impulses & tactile
sensory impulses from the mouth, food that
have pleasant tast increase salivary
secretion , also smooth texture food increase
the secretion .
Phases of salivary secretion :]
In addition to the salivation that occurs while
food in the mouth , salivation can occur even
before food enters the mouth, therefore,
salivary secretion divided into 3 phases :
1- psychic phase:it makes the mouth ready for
food & aid in the secretion of saliva as the
food is presented to the mouth
2- gastatory phase : supplies the saliva that
mixes with food while one is chewing
3- GI phase :continuous the secretion of saliva
even after the food passed for storage in the
stomach , this phase is especially likely to be
abundant when one has swallwed irritant food
because nerve signals from stomach then
excite the salivary nuclei, this helps to
neutralize the irritant substances thereby
relieving the irritation of stomach.
Esophageal secretion :
It is entirely mucoid , it provide lubrication for
swallwing , the main body of esophagus is
lined with many simple mucous glands in the
gastric end & in the initial portion of
esophagus , the mucous in the upper
esophagus prevents mucosal excoriation by
the newly entering food , whereas that near
esophago-gastric junction protect the
esophageal wall from digestion by gastric
juice , despite this protection peptic ulcer
may occure at the gastric end of esophagus .
Regulation of gastric acid secretion (nervous
& hormonal mechanism):
Basic facters that stimulate gastric secretion
(Ach , gastrin &histamine):
The neurotransmitters or hormones that
directly gastric secretion are ACH, gastrin
&histamine, all function by binding to
specific receptors
Gastric secretion :
In addition to mucus – secreting cell that line
the entire surface of the stomach , it has 2
important types of glands :
1- oxyntic (acid forming ) glands , secrete
Hcl, pepsinogen , intrinsic facter&mucus.
2- pyloric gland , secrete mainly mucus for
protection pyloric mucosa, some
pepsinogen, & gastrin hotrmone.
Stimulation of acid secretion
Nervous stimulation :
One half on nerve signals to the stomach that
cause gastric secretion originate in the
dorsal nuclei of the vagi&pass by vagus
nerve to the stomach then to the gastric
glands other half of signals generated by
local reflexes that occure in the enteric
nervous system, the type of stimuli that can
initiate reflexes are:distention , tactile ,
chemical stimuli.
Stimulation of acid secretion by gastrin:
The nerve signals from vagus nerve&from local
enteric reflex, beside causing direct
stimulation of glandular secretion of stomach
juices , also also stimulate the antral mucosa
to secrete gastrin hormone , it will carried by
blood to the oxyntic glands in the body of
stomach, it will stimulate the pariatal cells to
secrets Hcl (8x)which inturn excit local
enteric refllex activity which increase Hcl
secretion & increase the secretion of enzyme
by the peptic cell.