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11.16: Human Digestive System

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Do you know when you're digesting food?

Unless you have an upset stomach, digestion usually happens without you even noticing. You consciously chew up your food, but most of the digestive process takes place without your conscious awareness. Long after you put down your fork, food is still passing through your stomach and small intestine. It may take over a day for a meal to pass all the way through your digestive system.

Function of the Digestive System

Nutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get to your body cells? What organs and processes break down the foods and make the nutrients available to cells? The organs are those of the digestive system. The processes are digestion and absorption.

The digestive system is the body system that breaks down food and absorbs nutrients. It also gets rid of solid food waste. The digestive system is mainly one long tube from the mouth to the anus, known as the gastrointestinal tract (GI tract). The main organs of the digestive system include the esophagus, stomach and the intestine, and are pictured below ( Figure below ). The intestine is divided into the small and large intestine. The small intestine has three segments. The ileum is the longest segment of the small intestine, which is well over 10 feet long. The large intestine is about 5 feet long.

This drawing shows the major organs of the digestive system. The liver, pancreas and gallbladder are also organs of the digestive system.

Digestion is the process of breaking down food into nutrients. There are two types of digestion, mechanical and chemical. In mechanical digestion , large chunks of food are broken down into small pieces. Mechanical digestion begins in the mouth and involves physical processes, such as chewing. This process continues in the stomach as the food is mixed with digestive juices. In chemical digestion , large food molecules are broken down into small nutrient molecules. This is a chemical process which also begins in the mouth as saliva begins to break down food and continues in the stomach as stomach enzymes further digest the food.

Absorption is the process that allows substances you eat to be taken up by the blood. After food is broken down into small nutrient molecules, the molecules are absorbed by the blood. After absorption, the nutrient molecules travel in the bloodstream to cells throughout the body. This happens mostly in the small intestine.

Some substances in food cannot be broken down into nutrients. They remain behind in the digestive system after the nutrients are absorbed. Any substances in food that cannot be digested and absorbed pass out of the body as solid waste. The process of passing solid food waste out of the body is called elimination.

Vocabulary

  • absorption : Process that allows nutrients to be taken up by the blood.
  • chemical digestion : Process by which large food molecules are broken down into small nutrient molecules through a chemical process.
  • digestion : Process of breaking down food into nutrients.
  • digestive system : Body system that breaks down food, absorbs nutrients, and rids the body of solid food waste.
  • elimination : Process of passing solid food waste out of the body.
  • mechanical digestion : Process by which large chunks of food are broken down into small pieces through a physical process, such as chewing.
  • saliva : Watery substance located in the mouths of organisms, secreted by the salivary glands.

Summary

  • The digestive system is the body system that breaks down food, absorbs nutrients, and gets rid of solid wastes.
  • Digestion is the process of breaking down food into nutrients, while absorption is the process that allows nutrients to be taken up by the blood.

Practice

Use the resources below to answer the questions that follow.

  1. What type of muscles do you think you have in your esophagus?
  2. How long does food stay in your stomach? Where does it go next?
  3. What is the role of bile in the digestion process?
  1. Where does digestion start?
  2. Where are most of the nutrients from food absorbed? What happens to the nutrients once they are absorbed?
  3. What happens in the colon (large intestine)?
  4. What does the digestive system do to food?

Review

  1. What are three functions of the digestive system?
  2. What is the difference between mechanical and chemical digestion?

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Difficulty Level:

Basic

Grades:

7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Jun 16, 2014
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