<span>The submucosa<span> of the alimentary or the gastrointestinal tract contains numerous glands (i.e. gastric glands in the stomach, Brunner's glands in the duodenum) as well as numerous blood vessels. The submucosa also contains the submucosal nerve plexus or Meissner's plexus which functions to control the secretion of the submucosal glands.
</span><span><em>Another layer that has a nerve plexus is the muscularis layer which has the muscular nerve plexus or Auerbach's plexus which control the contractions of the gastrointestinal tract. The Meissner's and Auerbach's plexus are collective called the enteric nervous system.</em></span></span>
Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses.
