Complete Digestive Tract: Definition & Advantages

Lesson Transcript
Instructor: Amanda Robb

Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Learn about the complete digestive tract and the advantages of this type of digestive tract over incomplete digestive tracts. Discover how the complete digestive tract is structured and what organisms have this type of digestive tract. Updated: 12/13/2021

What Is a Digestive Tract?

As we snack on chips, veggies, or fruit while we work, we're getting some good energy to fuel our brains. However, where does this energy come from, and how do our bodies extract it from food? The answer is the digestive tract, which is a group of tissues or organs designed to break down food. Some animals, including humans, have a complete digestive tract, meaning it has a clear beginning (the mouth) and a separate end (the anus). Other, less complex animals, like sea sponges, or jellyfish, have only one opening.

These animals take in food from the same opening they release waste. Sound gross? Good thing humans have a complete digestive system! Let's look more closely at the human digestive tract.

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  • 0:00 What Is a Digestive Tract?
  • 0:47 The Human Digestive Tract
  • 2:11 Complete Digestive…
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The Human Digestive Tract

Humans, like other more complex animals, have a complete digestive tract. It starts at the mouth, where food is ground up and the digestion of carbohydrates, like those found in bread or sweets, begins. Next, the food is transported by the esophagus down to the stomach, which is a specialist in breaking down carbohydrates and some protein. It does this using tiny proteins called enzymes that speed up the chemical reaction of breaking down food. It also has an abundance of acid, which dissolves food into liquid.

Next, the food goes into the small intestine, a very different environment. The small intestine is basic, or lacks acid, unlike the stomach. This environment is suited for absorbing nutrients and breaking down mainly protein and fat. Here, we can see the advantage of efficient digestion. The stomach has a very harsh environment, perfect for liquefying food. But, the small intestine has a totally different environment for absorbing nutrients.

Since each organ is separate, they can do their jobs to the best of their abilities. After the small intestine is the large intestine, which absorbs water. Again, the structure and environment of the large intestine is different, so it can do a different job. After the large intestine is the rectum for storing waste and the anus for expelling waste. While the food moves through the digestive tract, a person is free to continue eating to gain more energy and nutrients.

Complete Digestive Tract Advantages

More recently evolved and more complex organisms usually have a complete digestive tract. Scientists think it evolved to provide two main advantages: to allow for continuous intake of food and to more efficiently absorb nutrients.

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