GIT and Saliva Study Quiz

GIT & Saliva

• The gastrointestinal (GIT) tract and saliva are topics for study.
• Objectives include differentiating between mesenteric and submucosal plexuses, explaining the autonomic nervous system's role in GIT function, and discussing saliva composition and secretion mechanisms.
• The enteric nervous system is entirely within the GIT wall.
• The system extends from the upper esophagus to the internal anal sphincter.
• It's composed of two plexuses: the myenteric (Auerbach's) and submucosal (Meissner's) plexuses.
• Both plexuses comprise intricate networks of fine, unmyelinated nerve fibers and neuronal cell bodies forming ganglia.

Enteric Nervous System

• The myenteric plexus (Auerbach's plexus) lies between the outer longitudinal and inner circular smooth muscle layers and extends from the upper esophagus to the anus.
• It's principally responsible for controlling gastrointestinal movements.
• Its neurons are multipolar.
• The submucosal plexus (Meissner's plexus) lies between the inner circular smooth muscle and the muscularis mucosae, also extending from the stomach to the anus.
• It primarily regulates gastrointestinal secretions and local blood flow.
• This plexus's neurons are bipolar or unipolar (sensory) and multipolar (interneurons).

Neurotransmitters

• Enteric neurons release a variety of neurotransmitters.
• Acetylcholine (ACh) is a key neurotransmitter, generally acting as an excitatory signal, stimulating smooth muscle contraction and increasing intestinal secretions.
• Norepinephrine (NE), derived from extrinsic sympathetic neurons, usually has an inhibitory effect, opposing ACh's actions.

Role of the Autonomic Nervous System

• The enteric nervous system functions autonomously but needs communication with the central nervous system.
• Parasympathetic and sympathetic fibers connect with the CNS and/or the enteric nervous system to affect the GIT.
• This connection allows signals from outside the digestive system to influence it, like the sight of food stimulating stomach secretions.
• Sympathetic stimulation usually inhibits GIT function and constricts blood vessels. Conversely, parasympathetic stimulation promotes digestive activity.
• The autonomic system modulates the enteric nervous system's activities in most cases.

Saliva

• Saliva is mostly water (approximately 99%), with a pH of 6.8–7.0.
• Important components include salivary amylase (for starch digestion), lingual lipase (activated by stomach acid to digest fat), mucus (lubrication and binding), lysozymes (antibacterial), and IgA (also antibacterial).
• Electrolytes like sodium, potassium, chloride, phosphate, and bicarbonate ions are present.
• Average daily saliva production is around 1000 mL.

Salivary Glands

• The main salivary glands are parotid, submandibular, and sublingual.
• Smaller glands are also located in the mouth's mucosa.
• Saliva has a critical role in oral health:
  • Moisten the mouth.
  • Digest starches and fat.
  • Cleanse the teeth.
  • Inhibit bacterial growth.
  • Dissolve molecules for taste.
  • Dilute and buffer food.
  • Moisten food & bind particles for swallowing

Saliva Secretion

• The major types of secretion in saliva include aqueous (serous) fluid containing water, ions, and digestive enzymes like ptyalin.
• The serous part is produced by the parotid, submandibular, and sublingual glands.
• Mucin-rich saliva (mucous secretion) is mainly created by the submandibular and sublingual glands.
• Parasympathetic signals are primary drivers of saliva production.

Simple and Conditioned Reflexes

• Simple reflexes involve direct stimulation within the oral cavity (e.g., food presence), triggering salivation.
• Conditioned reflexes (like mouth-watering from the smell of food) are associated with acquired responses.

Saliva Characteristics

• Aqueous fluids are also called serous secretions. These fluids contain water, ions and enzymes.
• Mucous secretions are rich in mucin.