1. SALIVARY ION AND FLUID SECRETION
Christopher Nosrat
Room: 3218
Phone:

2. SALIVARY ION AND FLUID SECRETION
References
Bradley, R.M Salivary secretion. Chapter 9 In Essentials of
Oral Physiology, pp , Mosby, St Louis.
Garrett, J.R. and Proctor, G.B Control of Salivation. In Linden, R.W.A. (ed.) The Scientific Basis of Eating. Front. Oral Biol., Basel, Karger pp
Petersen, O.H Electrophysiology of salivary
and Pancreatic Acinar Cells. Chapter 25 In Johnson, L.R. (Ed.)
Physiology of the Gastrointestinal Tract, pp , Raven, NY.
Petersen, O.H Secretion by the major salivary glands.
Chapter 26 In Johnson, L.R. (Ed.) Physiology of the
Gastrointestinal Tract, pp , Raven, NY.

3. SALIVARY ION AND FLUID SECRETION
SALIVARY GLAND DIVERSITY
STRUCTURE OF SALIVARY GLANDS
GLANDULAR MECHANISMS OF SECRETION
FACTORS AFFECTING FLOW
SECRETION OF WATER AND ELECTROLYTES

4. 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

5. 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

6. 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.

7. 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.

8. SALIVARY GLAND STRUCTURE
Salivary glands are made up of thousands of identical units

9. Saliva formed in acini flows down DUCTS to empty into the
THE SECRETORY UNIT
The basic building block of all salivary glands
Saliva formed in acini flows
down DUCTS to empty into the
oral cavity.
ACINI - water and ions
derived from plasma
enter here.

10. Components of a salivary gland
Autonomic nerve fibers
Myoepithelial cell
Ducts
Acini
Blood vessels

11. (Submandibular gland)
Serous salivary gland
(Parotid gland)
Mucous salivary gland
(Submandibular gland)

12. Mixed sero-mucous secretory unit
Striated ducts
Mixed sero-mucous secretory unit

13. Actions of nerves on salivary gland cells
Hydrokinetic - water mobilization
Protokinetic - protein secreting
Synthetic - inducing synthesis
Trophic - maintaining normal functional state and size

14. 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

15. GLANDULAR MECHANISMS OF SECRETION
FACTORS AFFECTING FLOW RATE
Time of day
Feeding
Stimulus frequency

16. CIRCAIDIAN RHYTHM OF SALIVA FLOW
No sleep
sleep
12 am
6 am
12 pm
6 pm 30 20 10
Time of day

17. Effect of feeding on salivary secretion
Meal
during
this
period
10 min collection periods

18. observed during feeding
Range of flow rates
observed during feeding
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)

19. GLANDULAR MECHANISMS OF SECRETION
FACTORS AFFECTING COMPOSITION
FLOW
PARASYMPATHETIC STIMULATION
SYMPATHETIC STIMULATION

20. ELECTROLYTE COMPOSITION OF HUMAN PAROTID SALIVA COMPARED WITH PLASMA

21. PROTEIN COMPOSITION OF HUMAN PAROTID SALIVA

22. Concentration (mM)
FLOW RATE ml/min

23. Parasympathetic
Sympathetic

25. Parasympathetic nervous system

26. 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.
carbachol
isoproterenol

27. NOTE different values on X and
Y 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.
120
100
Parasympathetic stimulation 80
Flow rate (µl/min) 60 40 20 50
100
150
200 14 12 10
Sympathetic stimulation
Flow rate (µl/min) 8 6 4 2 5 10 15 20
Stimulus frequency (Hz)

30. Area of secretory granules (µm2)
Control
3 mg/kg
30 mg/kg 50
100
150
Area of secretory granules (µm2)
Dose of isoproterenol

31. TWO STAGE HYPOTHESIS OF SALIVA FORMATION
Most proteins
Na+ Cl- resorbed
Hypotonic final saliva into mouth
Water & electrolytes
Some proteins electrolytes
K+ secreted
Isotonic
primary saliva

32. Concentration (mEq/l)
100 Na 80
HCO3 60
Concentration (mEq/l) Cl 40 20 K 10 20 30 40
Flow of saliva (ml/min)
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)

33. IONIC COMPOSITION OF PRIMARY SALIVA

34. 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?