Nutrition Science and Everyday Application - beta v 0.1

The Digestive System
We just learned that our body is composed of billions of cells. To function, these cells need
essential nutrients—carbohydrates, proteins, fats, vitamins, and minerals—which we obtain
from foods. However, before our cells can access these nutrients, foods need to be broken
down or digested into their simplest units, so that the nutrients can be absorbed and enter
the bloodstream. Digestion is a complex process that involves many organs and chemicals,
as we’ll explore on this page.
AN OVERVIEW OF THE ORGANS INVOLVED IN DIGESTION
The function of the digestive system is to break down the foods you eat, release their
nutrients, and absorb those nutrients into the body. Although the small intestine is the
workhorse of the system where the majority of digestion and absorption occurs, each of the
digestive system organs makes a vital contribution to this process.
The easiest way to understand the digestive system is to divide its organs into two main
categories: the gastrointestinal tract (GI tract) and the accessory organs.
• The GI tract is a one-way tube about 25 feet in length, beginning at the mouth and
ending at the anus. Between these two points, the GI tract also contains the
pharynx, esophagus, stomach, small and large intestines, and the rectum. The
small intestine is comprised of three parts: the duodenum, the jejunum, and the
ileum. The large intestine, also called the colon, is similarly divided into three
sections: the ascending colon, transverse colon, and descending colon. Both the
mouth and anus are open to the external environment; thus, food and wastes
within the GI tract are technically considered to be outside the body. Only through
the process of absorption do the nutrients in food enter into and nourish the
body’s “inner space.”
• Accessory organs, despite their name, are critical to the function of the digestive
system. They are considered accessory organs since they are not actually part of
the intestinal tract itself, but have ducts that deliver digestive juices into the tract to
help aid in digestion. There are four accessory organs: the salivary glands, liver,
gallbladder, and pancreas. All of these organs secrete fluids containing a variety of
chemicals such as enzymes and acids that aid in digestion.
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