SALIVARY ION AND FLUID SECRETION
Christopher NosratRoom: 3218Phone: 5 - 4388E-Mail: [email protected]
SALIVARY ION AND FLUID SECRETION
References
Bradley, R.M. 1995. Salivary secretion. Chapter 9 In Essentials of Oral Physiology, pp.161-184, Mosby, St Louis.
Garrett, J.R. and Proctor, G.B. 1998. Control of Salivation. In Linden, R.W.A. (ed.) The Scientific Basis of Eating. Front. Oral Biol., Basel, Karger pp. 135-155.
Petersen, O.H. 1994. Electrophysiology of salivary and Pancreatic Acinar Cells. Chapter 25 In Johnson, L.R. (Ed.) Physiology of the Gastrointestinal Tract, pp. 1025 -1059, Raven, NY.
Petersen, O.H. 1994. Secretion by the major salivary glands. Chapter 26 In Johnson, L.R. (Ed.) Physiology of the Gastrointestinal Tract, pp. 1061 -1117, Raven, NY.
References
Bradley, R.M. 1995. Salivary secretion. Chapter 9 In Essentials of Oral Physiology, pp.161-184, Mosby, St Louis.
Garrett, J.R. and Proctor, G.B. 1998. Control of Salivation. In Linden, R.W.A. (ed.) The Scientific Basis of Eating. Front. Oral Biol., Basel, Karger pp. 135-155.
Petersen, O.H. 1994. Electrophysiology of salivary and Pancreatic Acinar Cells. Chapter 25 In Johnson, L.R. (Ed.) Physiology of the Gastrointestinal Tract, pp. 1025 -1059, Raven, NY.
Petersen, O.H. 1994. Secretion by the major salivary glands. Chapter 26 In Johnson, L.R. (Ed.) Physiology of the Gastrointestinal Tract, pp. 1061 -1117, Raven, NY.
SALIVARY ION AND FLUID SECRETION
• SALIVARY GLAND DIVERSITY• STRUCTURE OF SALIVARY GLANDS• GLANDULAR MECHANISMS OF
SECRETION• FACTORS AFFECTING FLOW• SECRETION OF WATER AND
ELECTROLYTES
MAJOR FUNCTIONS OF SALIVA• Solvent• Anti-bacterial• Anti-fungal• Buffering• Lubrication• Remineralization• Temperature regulation• Production of growth factors and
other regulatory peptides• Digestion based on Essentials of Oral
Physiology by R. M. Bradley
A CONSIDERABLE VOLUME OF SALIVA IS PRODUCED OVER A DAY
• 0.5 to 0.75 liter of fluid is secreted in a day
• This represents about 1/5 of the total plasma volume
• This fluid is not lost as most of it is swallowed and reabsorbed by the gut
NO TWO SALIVARY GLANDS ARE THE SAME!
Much of the information on salivary secretion has been derived from the rat parotid gland.
Parotid glands in other species have different morphologies and physiology.
GENERAL RULES COMMON TO ALL SALIVARY GLANDS
1. Secretomotor autonomic nerves invariably control flow.
2. The osmotic pressure (tonicity) exerted by saliva is usually lower than plasma - saliva is usually hypotonic to plasma.
3. Tonicity increases as flow rate increases.4. Saliva contains potassium ions at 2-10 times the
concentration of serum potassium.5. Saliva in many animals contains a high level of
the digestive enzyme amylase.
SALIVARY GLAND STRUCTURE
Salivary glands are made up of thousands of identical units
THE SECRETORY UNITThe basic building block of all salivary glands
ACINI - water and ionsderived from plasma
enter here.
Saliva formed in acini flowsdown DUCTS to empty into the
oral cavity.
Components of a salivary glandAutonomic nerve fibers
Acini
Ducts
Blood vessels
Myoepithelial cell
Serous salivary gland
(Parotid gland)
Mucous salivary gland
(Submandibular gland)
Mucous secretory unit
Mixed sero-mucous secretory unit
Striated ducts
Actions of nerves on salivary gland cells
Hydrokinetic - water mobilization
Protokinetic - protein secreting
Synthetic - inducing synthesis
Trophic - maintaining normal functional state and size
Neural stimulation of myoepithelial cells
1. Speeds up the initial outflow of saliva
2. Reduces luminal volume
3. Contributes to secretory pressure
4. Supports underlying parenchyma
5. Helps the flow overcome increased
peripheral resistance
GLANDULAR MECHANISMS OF SECRETION
FACTORS AFFECTING FLOW RATE
Time of dayFeedingStimulus frequency
16
CIRCAIDIAN RHYTHM OF SALIVA FLOW
Time of day
No sleep
sleep
12 am 6 am 12 pm 6 pm 12 am 6 am 12 pm 6 pm 12 am
30
20
10
17
Effect of feeding on salivary secretion
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
10 min collection periods
Mealduringthis period
Classic experiment in which the nerve supply to the submandibular gland of a dog was stimulated electrically at different frequencies to initiate salivary flow.
Note the relationship between the frequency of stimulation and the salivary flow rate (Emmelin and Holmberg, 1967)
Range of flow ratesobserved during feeding
GLANDULAR MECHANISMS OF SECRETION
FACTORS AFFECTING COMPOSITION
• FLOW• PARASYMPATHETIC
STIMULATION• SYMPATHETIC STIMULATION
Resting Stimulated Plasma (mEq/L)Na+ 2.7 mEq/l 63.3 mEq/l 143.3K+ 46.3 mEq/l 18.7 mEq/l 4.1Cl- 31.5 mEq/l 35.9 mEq/l 100.9HCO3
- 0.6 mEq/l 29.7 mEq/l 27.5Mg2+ 0.45 mg/100 ml 0.04 mg/100ml 1.85Ca2+ 4.16 mg/100 ml 3.78 mg/100ml 2.47P(inorganic) 31.9 mg/100ml 9.7 mg/100ml 3.5 mg/100mlpH 5.82 7.67 7.4Osmolality 85.7 mOsm/kg 132.0 mOsm/kg 296.0 mOsm/kg
ELECTROLYTE COMPOSITION OF HUMAN PAROTID SALIVA COMPARED WITH PLASMA
PROTEIN COMPOSITION OF HUMAN PAROTID SALIVA
RESTING STIMULATED
Total protein 134.0 mg/100 ml 302.0 mg/100ml
Amylaseunits
340.6 528.0
FLOW RATE ml/min
Con
cen
trat
ion
(m
M)
Parasympathetic
Sympathetic
Sympathetic nervous system
Parasympathetic nervous system
TECHNIQUES TO STIMULATE EITHER THE PARASYMPATHETIC OR SYMPATHETIC
NERVOUS SYSTEM
Stimulate different branches of the autonomic nervous system - not practical in human experiments.
Use drugs that act at either the parasympathetic ( ) or sympathetic ( ) synapses with the salivary gland.
carbacholcarbachol
isoproterenolisoproterenol
0 5 10 15 20
0
2
4
6
810
12
14
Stimulus frequency (Hz)
Flo
w r
ate
(µl/m
in)
0 50 100 150 200
0
20
40
60
80
100
120NOTE differentvalues on X andY axes. High flow rates with parasympathetic stimulation when compared to sympathetic stimulation and no increases in flow rate after about 15 Hz for sympathetic stimulation. Flow rate plateaus out after 150 Hz for parasympathetic.
Sympathetic stimulation
Parasympathetic stimulation
Flo
w r
ate
(µl/m
in)
Control 3 mg/kg 30 mg/kg
050
100150
Are
a of
sec
reto
ry g
ranu
les
(µm
2 )
Dose of isoproterenol
TWO STAGE HYPOTHESIS OF SALIVA FORMATION
Water & electrolytes
Isotonic primary saliva
Most proteins
Some proteins electrolytes
Na+ Cl- resorbed
K+ secreted
Hypotonic final saliva into mouth
0 10 20 30 40
020
4060
80100
K
Cl
HCO3
NaC
once
ntr
atio
n (
mE
q/l
)
Classic experiment in which the concentration of ions in human parotid saliva was measured at different flow rates produced by
parasympathetic stimulation (Thaysen et al., 1954)
Flow of saliva (ml/min)
IONIC COMPOSITION OF PRIMARY SALIVA
Control Carbachol Isoproterenol Plasma
Na 136 139 136 147
K 8.5 4 5.5 4.4
QUESTIONS YOU SHOULD BE ABLE TO ANSWER
1. Where do salivary components come from?2. How is saliva formed?3. What makes saliva flow?4. What controls salivary flow rate?5. What are the underlying mechanisms of salivary reflexes?6. What good is saliva?7. What do salivary glands and saliva have in common?8. What differences are there between salivary glands and
saliva?9. What is the current hypothesis of the mechanism of salivary
secretion?10. What factors contribute to changes in salivary composition
and flow rate?