GI Phys 3

• four processes of the GI tract

  1.) motility

  2.) secretion

  3.) digestion

  4.) absorption
• first motility of the mouth and pharynx

  chewing (mastication) = grind food to increase surface area

  • mix with saliva to aid taste (chemoreception)
  • dissolve and liberate
• first motility of the mouth and pharynx

  voluntary skeletal muscles, but utilizes complex brainstem pattern

  • generators to organize and coordinate all the movements
  • lots of contact stimuli to get the patterns going and maintain movements within the mouth (e.g. using the tongue)
• secretion of the mouth and pharynx

  saliva = variety of functions

  • from three pairs of salivary glands
  • sublingual salivary gland
  • submandibular salivary gland
  • parotid salivary gland
• how does the autonomic nervous system affect secretion of saliva?

  Parasympathetic: lots, thin, watery, breaks down food

  Sympathetic: little, thick, viscous, not good for dissolving food
• water component in saliva

  99% of the saliva; moistens food and dissolves molecules to facilitate chemoreception
• mucus component in saliva

  lubricates food and facilitates formation of a bolus for swallowing
• HCO3- component in saliva

  neutralizes acids in foods and bacterial metabolites
• lysozyme component in saliva

  kills bacteria to maintain health of gums and teeth
• amylase component in saliva

  begins the digestion of polysaccharides (carbohydrates)
• lipase component in saliva

  begins the digestion of triglycerides and identifies fatty food source
• second motility of mouth and pharynx

  swallowing (deglutition) = propels food to stomach

  • two-phase process organized by a brainstem "swallow center"
• oropharyngeal phase

  first part

  • begins with voluntary closing of lips and elevation of tongue
  • irreversible reflex when bolus contacts back of oral cavity

  
• oropharyngeal phase

  second part

  • irreversible reflex when bolus contacts back of oral cavity
  • soft palate and uvula elevate to block off nasal passage

  
• oropharyngeal phase

  third part

  • soft palate and uvula elevate to block off nasal passage
  • larynx elevates & bolus flattens epiglottis over glottis
  • UES opens
  • (i.e. smooth muscle relaxes)

  
• oropharyngeal phase

  fourth part

  • larynx elevates, bolus flattens epiglottis over glottis, UES opens
  • UES closes rapidly. reducing eventual eructation, borborygmi, and flatuation

  
• esophageal phase

  peristaltic wave

  • propulsion only organized/regulated by brainstem
  • takes 5-9 seconds

  
• what does the local stretch of esophagus activate?

  secondary waves of peristalsis that increase propulsion of bolus (stronger)
• the first _/_ of esophagus is skeletal; all smooth muscle until anus after

  1/3
• LES or "cardiac" sphincter relaxes & bolus enters stomach

  weak LES gives rise to acid reflux = heartburn
• secretion of esophagus

  mucus = makes GI tract slippery and buffers acidity

  • protects the GI tract wall
  • buffers acidity with bicarbonate
• digestion and absorption of the esophagus

  essentially none = not enough time or enzymes

  • for mechanical digestion to take place