The Digestive Tube and Its Basic Processes Help

Introduction to The Digestive Tube and Its Basic Processes

Now we will look at another life-giving process – digestion – and its association with nutrition. Nutrition is the “process of nourishing,” while nutrients ( NEW -tree-unts) are “nourishing (substances).” Such nutrients (nourishing substances) would include, of course, glucose and other simple sugars, lipids, and proteins consumed for energy within our diet.

Digestion is literally the “process of separating or dividing (something) apart.” Formally speaking, digestion is the chemical and physical breakdown of food, thereby releasing its contained nutrients. But digestion and its breakdown is not an isolated process. It occurs along with many other related processes, and in the same anatomic location – within the digestive tube (Figure 19.1). The digestive tube is a tube that extends from the mouth (oral cavity) to the anus ( AY -nus), the small, muscular “ring” through which one defecates.

Fig. 19.1 The digestive tube and its general functions.

Ingestion And Egestion

Of the major processes associated with the digestive tube, ingestion ( in-JES -chun) is the first, while egestion ( ee-JES -chun) is the last. Ingestion is the “process of carrying (food) into” (in-) the digestive tube, while egestion is the “process of carrying (feces) out” (e-).

Digestion And Absorption

Absorption is the “process of swallowing (something) up.” In reality, absorption is a different process from the actual one of swallowing. Swallowing is the movement of food from the oral cavity, down into the pharynx (throat), and then into the esophagus (eh- SAHF -uh- gus ) or “gullet,” the muscular tube leading into the stomach.

Absorption is the movement of digested nutrients from the interior of the digestive tube, into the bloodstream. But we must remember that, quite often, the food we ingest consists of large chunks of food, far too big to be absorbed. (Picture a ham sandwich, with protein molecules in the ham and starch or carbohydrate molecules in the bread.)

Just because a particular foodstuff happens to be ingested through the mouth, does not necessarily mean that it can be digested (broken down) into smaller nutrients and absorbed. This digestive process is somewhat dependent upon the particular kind of stomach the food is entering, and the various digestive enzymes it may contain.

Secretion And Defecation

Digestion is often helped by the results of secretion – the release of various products from accessory digestive organs that are added to the digestive tube contents. The accessory digestive organs are organs attached to the sides of the digestive tube, but through which no food or feces actually passes. In humans, the accessory digestive organs include the salivary ( SAH -lih- vair -ee) glands, pancreas, liver, and gall bladder. These organs all add small quantities of various secretions to the digestive tube, which help in its process of breaking down big chunks of food into smaller molecules of nutrients.

Egestion is also called defecation ( deh -feh- KAY -shun), the excretion of unusable waste products within the feces or excrement.

Summary

The five basic processes involving the digestive tube are thus ingestion, digestion, secretion, absorption, and egestion (defecation).

Practice problems for these concepts can be found at:  Nutrition And The Digestive System Test