<P> Submucosal glands can refer to various racemose exocrine glands of the mucous type . These glands secrete mucus to facilitate the movement of particles along the body's various tubes, such as the throat and intestines . The mucosa is the lining of the tubes, like a kind of skin . Submucosal means that the actual gland resides in the connecting tissue below the mucosa . The submucosa is the tissue that connects the mucosa to the muscle outside the tube . </P> <P> The glands themselves are quite complex . The mucus factory is at the bottom, in the submucosa, it is composed of many little sacs (acini) where the mucus originates . Each sac (acinus) has one end that can open and close (dilate) to allow the mucus out . The acini empty into little tubes (tubules) that lead to a reservoir (collecting duct) that has a portal through the skin (mucosa) that can open and close allowing the mucus into the main tube . </P> <P> The submucosal glands are a companion to goblet cells which also produce mucus, and are found lining the same tubes . </P> <Ul> <Li> In the upper respiratory system of mammals there are submucosal glands in the airways, notably in the sinuses, the trachea and the bronchial tubes . </Li> <Li> In the visual systems of mammals . </Li> <Li> In the auditory systems of mammals . </Li> <Li> In the throat there are the esophageal glands, the submucosal glands of the esophagus . </Li> <Li> For the intestine there are Brunner's glands, the submucosal glands of the duodenum . </Li> </Ul>

Where are the submucosal glands located in the gastrointestinal tract