Physiology · MU Sofia

47. Composition and functions of the saliva and gastric juice. Regulation of saliva and gastric juice secretion.

Covers the composition and functions of saliva, including its electrolytes, enzymes and antimicrobial components, then sets out the parasympathetic and sympathetic control of its secretion. It goes on to the make-up of gastric juice, with the roles of hydrochloric acid, pepsin and intrinsic factor, and compares paracrine, neurocrine, hormonal and inhibitory regulation in a table. A further table lays out the cephalic, gastric and intestinal phases of acid secretion with their triggers, and the note closes with recap questions.

Inside: 8 sections · 3 labelled pictures · 2 tables · 15 flashcards · 3 min

Topic 47 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 8 sections, about 290 words (3 min of reading), with 15 flashcards.

In this note

  1. Composition and functions of the saliva and gastric juice. Regulation of saliva and gastric juice secretion.
  2. Saliva
  3. Functions
  4. Neural Regulation
  5. Gastric Juice
  6. Regulation of Gastric Juice Secretion
  7. Phases of HCl Secretion
  8. Recap Questions

Saliva

Composition

  • Water (99.5%)
  • Electrolytes: Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Magnesium (Mg²⁺), Chloride (Cl⁻), Bicarbonate (HCO₃⁻)
  • Mucus
  • White Blood Cells
  • Glycoproteins
  • Enzymes: Amylase (digests starch), Lipase (digests fats)
  • Antimicrobials: Immunoglobulin A (IgA), Lysozyme

Functions

  • Digestion: Lubricates and dissolves food for chewing and swallowing.
  • Protection: Irrigates mouth, flushes debris, prevents microbial infections.
  • Enzymatic Action: Initiates digestion of carbohydrates and lipids.
  • Speech & Taste: Aids in articulation and dissolves substances for taste reception.
  • Wound Healing: Growth factors in saliva aid mucosal repair.

Neural Regulation

Saliva secretion is entirely under autonomic (neural) control, not hormonal.

Parasympathetic Stimulation (Dominant)

  • Origin: Facial nerve (CN VII) & Glossopharyngeal nerve (CN IX)
  • Neurotransmitter: Acetylcholine (ACh)
  • Receptor: Muscarinic receptors on acinar cells
  • Second Messenger: IP₃ → ↑ Intracellular Ca²⁺
  • Effect: Profuse, watery saliva with low mucus content
  • Stimulators: Food, smell, nausea, chewing

Sympathetic Stimulation

  • Origin: T1–T3 spinal segments
  • Neurotransmitter: Norepinephrine
  • Receptor: β-adrenergic receptors
  • Second Messenger: cAMP (via adenylyl cyclase)
  • Effect: Low volume, viscous saliva with high mucus
  • Inhibitors: Sleep, fear, dehydration

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