Salivary secretions (Choudhury lecture) Flashcards
Saliva functions
Taste Lubrication Protection Digestion Speech Not essential for life
Salivary control
Saliva is under
neuronal control
not hormonal
(hormones modify)
Salivary glands
Salivary glands: (ectodermal)
Submandibular: serous/mucous 70% (thick saliva)
Sublingual: serous/mucous 5% (thick saliva)
Parotid (largest): serous 25% (thin saliva, no mucin)
Smaller glands: mucous
Constituents of saliva and their functions
Water facilitates speech, dissolving, tasting food, swallowing
Mucus lubrications, food into cohesive bolus
a-amylase (ptyalin) carbohydrate digestion, cleaves a-1,4 glycosidic bonds in starch (not essential)
Lingual lipase lipid digestion (milk-fats), hydrolysis of dietary lipid (not essential)
Ribonuclease RNA digestion (not essential)
Lysozyme antibacterial (bacillus & streptococcus), innate and acquired immunity
Lactoferrin chelates iron (inhibits microbial growth)
Lactoperoxidase antibacterial (kills bacteria in milk and mucosal lining)
Glycoprotein of IgA secretory IgA-immunologically active against virus and bacteria
EGF, NGF mucosal growth and protection
Kallikrein activates bradykinin – dilates arterioles, constricts veins increase blood
flow to secretory glands
Bicarbonate minimizes tooth decay (neutralizes bacterial acid)
(HCO3-) neutralizes refluxed gastric acid into lower esophagus (heartburn)
Hypotonic taste (can taste carbohydrates, fats and not protein –tofu!) Low osmolality
Two types of salivary glands
- serous (parotid- secretes non-viscous saliva composed of water, electrolytes and enzymes)
- mixed (submandibular, sublingual- secretes viscous saliva rich in mucin glycoproteins)
Salivary gland acini
primary secretion-saliva, plasma (H2O, Na+, Cl-, K+, HCO3-, amylase)
myopepithelial cells
motile, contracts, expels saliva
salivary gland ductal cells
modifies secretion by modifying electrolytes, Na+, Cl- reabsorbed K+, HCO3- secreted
- **Ductal cells are water impermeable, water is not absorbed along with the solute, water remains in lumen and saliva is secreted hypotonic relative to plasma
- **
Striated duct epithelium tight junction
H2O cannot leave duct
The story of salivary ions
Initial saliva is produced by acinar cells
Subsequently modified by ductal epithelial cells
Salivary ducts are impermeable to water and sodium is continually reabsorbed
Lumen of ductal cells contains
3 transporters:
- Na +- H + exchange,
- Cl - HCO 3 exchange, and
- H +- K + exchange
Basolateral membrane contains:
- Na +/K + ATPase and Cl channels
Net absorption of Na + & Cl causes
NaCl in saliva lower than in plasma
Net secretion of K + and HCO 3 causes
K + and HCO 3 in saliva higher than in
plasma
Changes in ionic composition of saliva
Ionic composition of saliva changes as salivary flow rate changes
Duct cells modifies the composition of saliva
At highest flow rates (4 mL/min), final saliva resembles plasma (high Na+, Cl-, low K+)
as the ductal cells have less time to modify the saliva
At lowest flow rates (
The short story on neuronal regulation of saliva
Both Symp and Parasymp stimulates secretion
Parasymp stimulates more than Symp
Parasymp: major M3 receptors, increase secretion of watery saliva
Symp: major b receptors, increase viscous saliva, minor a receptors – watery saliva
The long story on regulation of saliva
Salivary acinar & ductal cells have both Symp and
Parasymp innervation
Neuronal: ANS (symp & parasymp) stimulate &
regulate the flow of salivary gland secretions
Symp NS stimulates secretion:
- increases cAMP (major), increase amylase secretion
- increases IP3 (minor), increase fluid secretion
Parasymp NS stimulate secretion -Dominant
- increases IP3 (major), increase fluid secretion
- vasodilation to surrounding blood vessels
- activation of both acinar & duct cells transporter
- releases kallikrein
- greater influence than Symp NS
Hormonal:
- ADH (antidiuretic hormone) &
- Aldosterone modify composition of saliva Na +, K +
- Kallikrein produces bradykinin (potent vasodilator),
increases blood flow and increase salivary secretions
Salivary regulation compared to rest of GI tract
Salivary secretion and composition are controlled solely by the autonomic nervous system, in contrast, other parts of the GI tract include local reflexes and hormonal mechanisms as well
Stimulation and inhibition of saliva
CNS and its ANS respond to external
events and either stimulate or inhibit
activities of salivary glands
Stimulated by:
smell, taste, sound, sight, chewing,
spicy or sour tasting foods, smoking,
nausea, vomiting, sympathomimetic
(ephinephrine), parasympathomimetics
(acetylcholine, pilocarpine, muscarine),
histamine, etc.
Inhibited by:
sleep, fear, shock, anti depressants,
fever, dehydration, fatigue,
antihistamines, anti-parkinson drugs,
anti-muscarinic drugs, marijuana
(anti-cholinergics lead to dry mouth)
monoamine oxidase inhibitors, etc.
