<P> There are many specialised cells of the GI tract . These include the various cells of the gastric glands, taste cells, pancreatic duct cells, enterocytes and microfold cells . </P> <P> Some parts of the digestive system are also part of the excretory system, including the large intestine . </P> <P> The mouth is the first part of the gastrointestinal tract and is equipped with several structures that begin the first processes of digestion . These include salivary glands, teeth and the tongue . The mouth consists of two regions; the vestibule and the oral cavity proper . The vestibule is the area between the teeth, lips and cheeks, and the rest is the oral cavity proper . Most of the oral cavity is lined with oral mucosa, a mucous membrane that produces a lubricating mucus, of which only a small amount is needed . Mucous membranes vary in structure in the different regions of the body but they all produce a lubricating mucus, which is either secreted by surface cells or more usually by underlying glands . The mucous membrane in the mouth continues as the thin mucosa which lines the bases of the teeth . The main component of mucus is a glycoprotein called mucin and the type secreted varies according to the region involved . Mucin is viscous, clear, and clinging . Underlying the mucous membrane in the mouth is a thin layer of smooth muscle tissue and the loose connection to the membrane gives it its great elasticity . It covers the cheeks, inner surfaces of the lips, and floor of the mouth . </P> <P> The roof of the mouth is termed the palate and it separates the oral cavity from the nasal cavity . The palate is hard at the front of the mouth since the overlying mucosa is covering a plate of bone; it is softer and more pliable at the back being made of muscle and connective tissue, and it can move to swallow food and liquids . The soft palate ends at the uvula . The surface of the hard palate allows for the pressure needed in eating food, to leave the nasal passage clear . The lips are the mouth's front boundary and the fauces (the passageway between the tonsils, also called the throat), mark its posterior boundary . </P>

How does the oral cavity help the digestive system