Table 3-2 .—Principal digestive juices, source and action
| Source | Digestive juice | Substance acted upon | Product |
| Salivary glands | Ptyalin | Starch | Complex sugar (maltose) |
| Gastric glands | Hydrochloric acid (HCl) | Pepsinogen Proteins | Pepsin Split proteins (proteoses, peptones) |
| Liver | Bile | Fats | Emulsified fats |
| Pancreas | Amylase | Starch | Complex sugar (maltose) |
| Proteinases (trypsin, chymotrypsin) | Proteins, split proteins | Peptides, polypeptides | |
| Lipase | Fats | Fatty acids, glycerol | |
| Intestinal glands | Carbohydrates (maltase, sucrase, lactase) | Complex sugars (maltose, sucrose, lactose) | Simple sugars (glucose fructose, galactose) |
| Peptidases | Peptides polypeptides | Amino Acids | |
| Lipase | Fats | 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 complex 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 mastication, 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 being swallowed down the pharynx. Food is deflected away from the trachea to prevent particle aspiration.
