SALIVARY ION AND FLUID SECRETION

Christopher NosratRoom: 3218Phone: 5 - 4388E-Mail: nosrat@umich.edu

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?