1. The Digestive and Excretory Systems
In this lesson, you will Learn About…
How your body digests food.
How your body removes waste products.

2. The Digestive and Excretory Systems
The Vocabulary terms in this lesson are:
Digestion.
Digestive system.
Saliva.
Small intestine.
Liver.
Pancreas.
Excretion.
Excretory system.
Colon.
Kidneys.
Click each term to display its definition.

3. Useful Material Extracted
Turning Food into Fuel
When you eat, your body’s digestive system breaks the food down into smaller parts so it can use the nutrients in the food for fuel. This is the process of digestion.
Small Intestine
Useful Material Extracted
Mouth
Crushing and Grinding
Stomach
Chemical Breakdown
Colon
Water Removal
Digestion involves physical changes, such as the crushing of food by the teeth. It also involves chemical changes, such as the transforming of food by substances in the body called enzymes.
Waste Elimination

4. How Digestion Begins
Saliva is a digestive juice produced by the salivary glands in your mouth. It starts to flow as a physical signal from your body that it is ready to begin the digestive process.
When you chew your food and swallow it, your body initiates the digestive process.

5. Chewing and Swallowing1
The teeth tear and grind the food into small shreds or chunks.
The salivary glands produce saliva. Enzymes in saliva begin the chemical breakdown of carbohydrates. Moistens and softens food for its transport 2 3
When you swallow, a flap of skin called the epiglottis closes off the trachea to keep food from entering it. At the same time, the uvula closes off the airway to the nose.
The teeth tear and grind the food into small shreds or chunks.
The salivary glands produce saliva. Enzymes in the saliva begin the chemical breakdown of carbohydrates, converting the starches to sugar. The saliva also moistens and softens the food for its transport.
Before swallowing the food, the air passages are open. Getting food into these passages could cause choking. Therefore, when a person swallows, a flap of skin called the epiglottis closes off the trachea to keep food from entering it. The trachea, or windpipe, is the passageway through which air gets to the lungs. At the same time, the uvula closes off the airway to the nose.
Once the food is swallowed, it enters the esophagus, a long muscular tube that connects the mouth to the stomach. 4
Once the food is swallowed, it enters the esophagus. Pushes the food along until it reaches the stomach.

6. Organs of the Digestive System
After the liver produces bile, it sends it to the gallbladder. 4
Acid and enzymes in the stomach break down food until it resembles a thin soup called chyme. 1
The pancreas produces pancreatic juice to break down proteins, carbohydrates, and fats. 5
Next the food moves to the small intestine. Most of digestion takes place here. 2
This is the path food takes during the next part of the digestive process:
The esophagus pushes the food along until it reaches the stomach. The stomach’s strong, muscular walls churn the food to break it into smaller pieces and mix them with gastric juice, a mixture of acid and enzymes. This process can take up to four hours.
Acid and enzymes in the stomach break the food down until it resembles a thin soup called chyme.
Next, the food moves to the small intestine, a coiled tube, about 20 feet long, where most of the digestive process takes place.
The liver, the body’s largest gland, secretes a liquid called bile that helps to digest fats. In addition, the liver helps regulate the level of sugar in the blood, breaks down harmful substances such as alcohol, and stores some vitamins.
After the liver produces bile, it sends it to the gallbladder. The gallbladder stores the bile until it is needed.
The pancreas is a gland that helps the small intestine by producing pancreatic juice, a blend of enzymes that break down proteins, carbohydrates, and fats.
The walls of the small intestine are covered with fingerlike projections called villi. Nutrients from the digested material pass through the villi. This allows the nutrients to enter the bloodstream and eventually reach body cells.
The liver secretes bile to help digest fats. 3
Nutrients from the digested material pass through the small intestine. Villi, bloodstream, body cells. 6

7. Removing Wastes from the Body
Some foods that you eat contain substances that the body cannot use.
During the digestive process, these wastes are separated out.
The wastes are removed from the body through a process called excretion. The major organs of the excretory system are the kidneys, bladder, and colon.
The body produces three kinds of wastes: solids, liquids, and gases. Although the lungs get rid of carbon dioxide gas when one exhales, and the skin gets rid of some wastes when one sweats, the major organs of the excretory system are the kidneys, bladder, and colon.

8. Eliminating Liquid Wastes1
The kidneys filter water and waste materials from the blood. 2
The kidneys send the urine to the bladder through two tubes called ureters. 3
The urine is stored in the bladder.
Liquid wastes are produced by cell activity. Approximately 50 to 80 percent of the body is water and most waste materials are dissolved in it. Here’s how the kidneys and the bladder filter, store, and finally remove these wastes from the body.
The kidneys are a pair of organs that filter water and waste materials from the blood. The kidneys also help to regulate the amounts of water and salt in the body. Urine is made up of the fluid and dissolved substances secreted by the kidneys.
The kidneys send the urine to the bladder through two tubes called ureters.
The bladder is a pouch in which urine is stored.
A signal from the nervous system lets the person know when the bladder is full. Urine passes out of the body through a tube called the urethra. 4
Urine passes out of the body through a tube called the urethra.

9. Solid Wastes
Solid wastes are made up of foods that your body cannot break down, including fiber.
After digestion, the body sends a mixture of water and undigested solid wastes into the colon.
Most of the water is absorbed by the colon and returned to the body. The remaining solid wastes become material called feces.
The colon is also called the large intestine. When the colon becomes full, strong muscles in its walls contract. This movement pushes the feces out of the body through an opening called the anus.

10. Caring for Your Digestive and Excretory Systems
To keep the digestive and excretory systems working well:
Eat a balanced diet that is based on the Food Guide Pyramid.
Eat plenty of foods that are low in fat and high in fiber.
Eat at regular times each day.
Drink eight to ten glasses of water every day.
Take care of your teeth.
Stay active.
Explain the tips on the slide using the points below:
Eat a balanced diet that is based on the Food Guide Pyramid. Eating a variety of foods while taking care not to eat too many foods from the tip of the Pyramid promotes healthy digestion.
Eat plenty of foods that are low in fat and high in fiber. Dietary fiber helps moves wastes through the digestive system.
Eat at regular times each day. This habit will keep foods moving through the body at a steady pace.
Drink eight to ten glasses of water every day. The digestive and excretory systems need plenty of water in order to function. Foods that contain large amounts of water, such as fruit, soup, and juice, also count.
Take care of the teeth. The teeth are important to the digestive process. Teens should brush them at least twice a day with a fluoride toothpaste, and floss daily. Regular dental checkups are very important.
Stay active. Regular physical activity aids digestion. Teens should participate in moderate to physical activity on most, if not all, days of the week. Waiting a while after eating, before engaging in physical activity gives the body time to digest some of the food eaten.

11. Reviewing Terms and Facts
Define the term digestion.
Digestion is the process by which the body breaks down food into smaller components that can be absorbed by the bloodstream and sent to each cell in the body.
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12. Reviewing Terms and Facts
Identify the major organs of the excretory system.
Kidneys
Bladder
Colon
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13. Thinking Critically
Describe possible consequences for the rest of the body if the digestive system is not working properly.
Reponses will vary, but should provide specifics on how the body will not function properly if it does not get the necessary nutrients.

14. Vocabulary Review
Digestion is the process by which the body breaks down food into smaller components that can be absorbed by the bloodstream and sent to each cell in the body.
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15. Vocabulary Review
The digestive system is a group of organs that work together to break down foods into substances that the cells can use.
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16. Vocabulary Review
Saliva is a digestive juice produced by the salivary glands in the mouth.
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17. Vocabulary Review
The small intestine is a coiled tube, about 20 feet long, where most of the digestive process takes place.
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18. Vocabulary Review
The liver, the body’s largest gland, secretes a liquid called bile that helps to digest fats.
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19. Vocabulary Review
The pancreas is a gland that helps the small intestine by producing pancreatic juice, a blend of enzymes that breaks down proteins, carbohydrates, and fats.
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20. Vocabulary Review
Excretion is the process by which the body gets rid of waste materials.
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21. Vocabulary Review
The excretory system is the system that removes wastes from the body and controls water balance.
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22. Vocabulary Review The colon is a storage tube for solid wastes.
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23. Vocabulary Review
The kidneys are a pair of organs that filter water and waste materials from the blood.
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