parasympathetic:
A. Sublingual & submandibular
Chorda tympani (branch of facial N.; 7 th cranial N.)
1. Superior salivary center ( SSC) in the lower part of
pons.
2. Chorda Tympani
3. Submaxillary ganglion
4. Postganglionic cholinergic fibers.
5. Salivary glands (sublingual & submandibular)
parasympathetic Parotid gland:
- Superficial petrosal nerve (branch of glossopharyngeal
nerve; 9th cranial N.)
1. Inferior salivary center (ISC) in the upper part of
medulla oblongata.
2. Superficial petrosal N.
3. Otic ganglion.
4. Postganglionic cholinergic fibres.
5. Parotid gland.
Sympathetic of salivary glands.
From the LHCs of the upper 2 thoracic segments
of the spinal cord (under control of SSC & ISC).
- Relay in superior cervical ganglion (SCG)
- Postganglionic noradrenergic fibers supply the
salivary glands.
Parasympathetic stimulation: Produces: ( salivary)
- profuse watery secretion rich in electrolytes &
poor in organic substances (enzymes & mucin). - VD of salivary blood vessels.
WHILE, sympathetic stimulation produces: ( salivary)
- Trophic secretion (small in volume & rich in
enzymes). - VC of salivary blood vessels.
- Contraction of myoepithelial cells.
Augmented salivary secretion
Mechanism: may be
- Contraction of the myoepithelial cells.
- Parasympathetic stimulation increases the
sensitivity of the gland to sympathetic stimulation.
Composition of saliva
Organic substances: , Inorganic substances:
Volume, pH
Volume: 800 –1500 ml/day (average 1000 ml/day).
pH: 6-7 (favorable for the action of ptyaline).
1. Water : 99.5%.
2. Organic substances:
- Alpha amylase enzyme (ptyaline) in serous
secretion.
- Lysozyme enzyme.
- Mucin (mucus secretion) for lubricating and for surface protective purposes.
- Proteins e.g. albumin, globulin.
- Small amount of urea & glucose.
3. Inorganic substances:
Nacl, Kcl (cl - acts as activator for amylase
enzyme).
Buffer systems:
Bicarbonate (H2co3 +NaHco3).
Phosphate (Monosodium phosphate; Na H2po4
& disodium phosphate; Na 2Hpo4).
Soluble calcium salts.
Functions of saliva
- Digestion: of cooked starch (by amylase
enzyme). - Deglutition (swallowing).
- Articulation (speech).
- Solving action.
- Antibacterial action & cleaning of mouth.
- Excretion e.g. urea, mercury, lead, iodine &
fluorine. 7. Buffering action. 8. Water balance.
Mechanism of salivary secretion
- Conditioned reflex. “ Pavlov’s experiment.”
- Unconditioned reflex.
A. Buccal: • Chemical & mechanical stimulation of buccal
mucosa. Afferent impulses from anterior 2/3 of the
tongue (carried by chorda tympani) and from
posterior 1/3 of the tongue (by
glossopharyngeal) to the salivary centers in
brain stem which give efferent sympathetic &
parasympathetic.
B. Esophageogastric B. Esophageogastric: - Distension of esophageogastric junction causes
stimulation of gastric mucosa by food or irritant
substances.
Afferent impulses are carried along the vagus
nerve to the salivary centers in brain stem which give efferent sympathetic & parasympathetic.
Theories of salivary secretion
A. Simple filtration diffusion theory. B. Active secretion theory.
Evidences:
1. Increased O2 consumption & glucose utilization
by the gland.
2. Composition of saliva is different from
plasma.
3. Pressure of submandibular gland is 140 mmHg
during secretion.
4. Small dose of atropine stops salivary secretion.
5. Stimulation of chorda tympani nerve decrease the
volume of submandibular gland.
Saliva contains especially
large quantities of K+ &
Hco3- ions.
Conversely, the concentrations of both sodium &
chloride ions are several times less in saliva than in
plasma.
Salivary secretion is a two-stage operation:
first stage involves the acini, and the second stage, the salivary ducts.
The acini secrete a primary secretion that contains
ptyalin and/or mucin in a solution of ions in concentrations not greatly different from those of typical ECF.
the primary secretion flows through the ducts,
The net result is that under resting conditions , the
……………..
During maximal salivation,……..
concentrations of Na+ & cl- ions in the saliva are
only about 15 mEq/L each, about 1/7 to 1/10 their
concentrations in plas
Na cl concentration rises only to ½
or 2/3 that of plasma, and the K+ concentration
rises to only 4 times that of plasma.
primary secretion by the acini
can increase as much as 20-fold. This acinar
secretion then flows through the ducts so rapidly
that the ductal reconditioning of the secretion is
considerably reduced.
