Table 3-2 .—Principal digestive juices, source and action Source Digestive  juice Substance acted Product upon Salivary glands Ptyalin Gastric glands Hydrochloric   acid (HCl) Liver Bile Pancreas Amylase Proteinases (trypsin, chymotrypsin) Lipase Intestinal   glands Carbohydrates (maltase, sucrase, lactase) Peptidases Lipase Starch Pepsinogen Proteins Fats Starch Proteins,  split proteins Fats Complex  sugars (maltose, sucrose, lactose) Peptides polypeptides Fats Complex  sugar (maltose) Pepsin Split proteins (proteoses, peptones) Emulsified  fats Complex  sugar (maltose) Peptides,  polypeptides Fatty acids, glycerol Simple sugars (glucose fructose, galactose) Amino   Acids Fatty acids, glycerol the  aid  of  digestive  enzymes,  into  solutions  and simple compounds. Carbohydrates (starches and sugars) change into simple sugars (glucose); fats change into fatty acids; and proteins change into amino  acids. MOUTH In the mouth the TEETH mechanically break up  food  into  small  particles  before  it  is  swallowed. The salivary glands—parotid, submaxillary, and sublingual—secrete  saliva,  which  moistens  the food, makes it easier to chew, and lubricates the food  mass  to  aid  in  swallowing.  About  1,500  ml of  saliva  are  secreted  daily.  Saliva  contains  one principal enzyme, ptyalin, which initiates chemical digestion  of  starches,  breaking  them  into  the  com- plex sugar maltose. The  TONGUE  is  a  muscular  organ  attached to  the  lower  jaw  at  the  back  of  the  mouth  and is the chief organ of taste. It assists in mastica- tion,  swallowing,  and  speech. PHARYNX The pharynx (see The Respiratory System) is the   passageway   between   the   mouth   and   the esophagus and is shared with the respiratory tract. The  EPIGLOTTIS  is  a  cartilaginous  flap  that closes the opening to the larynx when food is be- ing  swallowed  down  the  pharynx.  Food  is  de- flected away from the trachea to prevent particle aspiration. 3-43