b. The pancreas, linked to the small intestine by a series of small ducts, is made
up of exocrine cells and endocrine cells. Exocrine cells empty their products into the
pancreas duct network. Endocrine cells distribute their products into the circulatory
system. Another name for endocrine cells is islands or islets of Langerhans. Endocrine
cells make up about two percent of the total pancreas mass and are made up of alpha,
beta, and delta cells that secrete hormones.
1-12. APPENDIX--ACCESSORY STRUCTURE
The appendix is attached to the cecum of the large intestine. This organ is a
worm-like structure that has no functional importance in the digestive process. See
figure 1-1 for position of the appendix.
Section II. FUNCTIONS AND STAGES OF THE DIGESTIVE PROCESS
1-13. MECHANICAL AND CHEMICAL DIGESTION
There are two major types of digestion: mechanical digestion and chemical
digestion. Mechanical digestion refers to the various movements that help food move
through the digestive system. Chemical digestion refers to the series of catabolic
reactions (here, the breakdown of bonds of food molecules to release energy) that
break down large carbohydrate, lipid, and protein molecules which are in the food we
have eaten. The broken down molecules are used by the cells of the body to produce
a. Mouth. Both mechanical digestion and chemical digestion take place in the
(1) Mechanical digestion. The first step in mechanical digestion in the
mouth is mastication, more commonly called chewing. The tongue moves food around
in the mouth, the teeth chew the food, and food is mixed with saliva during this process.
The result is that food is reduced to a soft, flexible mass called a bolus. The second
mechanical function that occurs in the mouth is deglutition, also called swallowing. In
swallowing, the tongue moves the bolus upward and backward against the palate
forcing the bolus to the back of the mouth cavity and into the oropharynx (a voluntary
stage of swallowing). Next, the involuntary pharyngeal stage of swallowing takes place,
and the bolus passes through the pharynx and enters the esophagus. Note that the
tongue is important in both mastication and deglutition.
(2) Chemical digestion. Only one chemical digestive process occurs in the
mouth. The enzyme salivary amylase begins the breakdown of starch. The function of
this enzyme is to aid in the breakdown of carbohydrates. Most food is swallowed too
quickly for it to be broken down to substances which the body can use. The enzyme
salivary amylase continues to act on starches in the food for 15 to 20 minutes while the
food is in the stomach.