Module 13B: Saliva and Salivation

Topic context

  • Topic: Saliva and salivation control
  • Source: PHY2032 GUT SECRETIONS, Dr. Julia Choate
  • Core question: What is saliva and how do we regulate salivation?

Normal volumes and pH of secretions into the GI tract

  • Saliva: volume 1000\ \mathrm{mL}, pH 7.0-8.0
  • Stomach: volume 1500\ \mathrm{mL}, pH 1.0-3.5
  • Pancreas: volume 1000\ \mathrm{mL}, pH 8.0-8.3
  • Bile: volume 1000\ \mathrm{mL}, pH 7.8
  • Small intestine: volume 1800\ \mathrm{mL}, pH 7.5-8.0
  • Large intestine: volume 200\ \mathrm{mL}, pH 7.5-8.0
  • Total GI secretions: 6700\ \mathrm{mL}

Why do we salivate? What controls salivation?

  • Saliva serves multiple roles in oral processing and digestion; it is essential for lubrication, initial digestion, protection of oral tissues, regulation of water intake, speech, taste, and swallowing.
  • Salivation is regulated by neural control, with parasympathetic input playing a major role in controlling rate and volume.

Saliva is secreted from salivary glands

  • Extrinsic glands (3 pairs): parotid, submandibular, sublingual
  • Intrinsic buccal salivary glands are also involved
  • Gland types:
    • Parotid gland
    • Submandibular gland
    • Sublingual gland

All about saliva

  • Daily secretion: 800-1500\ \mathrm{mL} (average 1000\ \mathrm{mL})
  • Flow rates (relative to state):
    • Sleep: 0.05\ \mathrm{mL/min}
    • Awake: 0.5\ \mathrm{mL/min}
    • With acid (stimulated): 7-8\ \mathrm{mL/min}
  • pH depends on flow rate: ranges from 6.2-8.0
  • Composition:
    • Water: 97-99.5\%
    • Ions: Na+, K+, Ca^{2+}, Mg^{2+}, PO4^{3-}, HCO3^{-}, Cl^{-}
    • Salivary amylase (ptyalin)
    • Mucin
    • Immunoglobulins

Functions of saliva

  • Lubrication
  • Digestion
  • Protection of oral tissues
  • Control of water intake
  • Speech
  • Absorption (pre-absorptive oral processes)
  • Taste sensation

Regulation of salivary secretion

  • Predominantly regulated by parasympathetic nerves
  • Triggers include:
    • Sleep, fear
    • Olfactory, gustatory, visual, auditory cues
    • Cortical input: salivation anticipation (approach of food, thought of food, smell, sound, sight)
    • Presence of food in the mouth (touch, taste)
    • Nausea

Treatments targeting muscarinic receptors (ACh) for saliva disorders

  • Principle: modulation of parasympathetic activity at muscarinic receptors on salivary glands
  • Targeted action: muscarinic receptor agonists or antagonists to adjust saliva production

Treatment of excessive salivation (ptyalism/drooling)

  • Approach: Muscarinic receptor inhibitor/antagonist
  • Example/product: Sal-Tropine tablets
  • Mechanism: reduce salivation by inhibiting muscarinic receptors
  • Dosing example: Sal-Tropine 0.4 mg tablets (Atropine sulfate, U.S.P.)
  • Product specifics:
    • Brand: Sal-Tropine
    • Regulatory code: OC 60267-742-30
    • Package example: 100 tablets
  • Clinical goal: prevent hygiene problems and remove social barriers due to drooling or excess saliva
  • Example formulation: Sal-Tropine (Atropine sulfate, U.S.P.) 0.4 mg tablets

Xerostomia (dry mouth) due to insufficient salivation

  • Main causes:
    • Drugs
    • Radiotherapy
    • Dehydration
    • Shock
    • Renal failure
  • Consequences:
    • Oral diseases including dental cavities
    • Gum disease
    • Bad breath
    • Constant thirst sensation
    • Altered taste sensations
    • Compromised chewing, swallowing, and speech
    • Note: possible association with consumption of acidic agents (e.g., 5% citric acid)
  • Diagnosis and treatment:
    • Diagnosis: assess salivary flow and related symptoms
    • Treatment: muscarinic receptor agonists to stimulate saliva; withdraw offending drug if possible

Summary of salivation

  • Saliva is secreted from both extrinsic and intrinsic salivary glands
  • Main functions: lubrication, digestion, protection, control of water intake, speech, taste
  • Parasympathetic nerves modulate the rate of salivation
  • Abnormal salivation states (ptyalism/drooling and xerostomia) are managed with drugs acting on muscarinic receptors on the salivary gland epithelium