Digestion of the major foodstuffs is an orderly process involving the action large number of digestive enzymes.
句子主干：digestion主语 （of结构为定语 ）is系词process表语（involving到句末为宾语的后置定语）
Some of these enzymes are found in the secrtions of the salivary glands,the stomach,and the exocrine portion of the pancreas.
句子主干：Some of these enzymes主语；are found谓语.in以后为地点状语
Other enzymes are found in the luminal membranes and the cytoplasm of the cells that line the small intestine.
句子主干：主语谓语与上句相类似.cell后that从句为定语从句,修饰cells
The action of the enzymes is aided by the hydrochloric acid secreted by the stomach
and the bile secreted by the liver.
句子主干：The action主语；is aided谓语；by the hydrochloric acid为谓语的补语,（the bile也是by的宾语）secreted by the stomach为过去分词形式的后置定语