Lesson #4: Digestive System

Turn and Talk: Based off this information, do you think that the marathon runner didn't eat enough the day of the race? 

How the Digestive System Works and When It Does Not

The digestive system is responsible for breaking food down into smaller molecules that the body can use for energy, growth, and repair. Digestion begins in the mouth, where food is physically broken apart by chewing and mixed with saliva. After swallowing, food moves through the esophagus and into the stomach. In the stomach, muscles churn the food while acids and enzymes begin breaking large food molecules into smaller ones.

After leaving the stomach, the partially digested food enters the small intestine. The small intestine is where most digestion and absorption take place. Enzymes released from the pancreas and the lining of the small intestine break carbohydrates into simple sugars, proteins into amino acids, and fats into fatty acids and glycerol. These smaller organic molecules are now small enough to move across the wall of the small intestine.

The inner surface of the small intestine contains tiny finger-like structures called villi. Each villus increases the surface area of the intestine and contains many blood capillaries. Organic molecules move from the small intestine into the blood by diffusion. Diffusion occurs when molecules move from an area of higher concentration in the intestine to an area of lower concentration in the blood. Once in the bloodstream, these molecules are transported to cells throughout the body.

In some patients, a disease called celiac disease interferes with this process. Celiac disease is a condition in which the immune system reacts to a protein found in wheat, barley, and rye. This immune response damages the villi lining the small intestine. Over time, the villi become flattened and less effective at absorbing nutrients.

When the villi are damaged, diffusion of organic molecules into the blood is reduced. Even though food is digested into smaller molecules, fewer nutrients are able to pass into the bloodstream. As a result, patients may experience fatigue, weight loss, or poor growth because their cells are not receiving enough nutrients. This disease shows how the structure of the digestive system is directly related to its function, and how damage to that structure can disrupt normal body processes.

Tier 2 Vocabulary 

1. Process: A series of steps that happen in a specific order.
   
   

2. Interferes: Gets in the way of something working correctly.
   
   

3. Disrupt: To interrupt or stop something from working normally.
   
   

4. Absorption: The movement of something from one place into another.
   
   

5. Reduced: Made smaller or less effective.
   
   

Tier 3 Vocabulary 

• Digestive system: A group of organs that work together to break down food and absorb nutrients.
  
  

• Esophagus: A muscular tube that moves food from the mouth to the stomach.
  
  

• Stomach: An organ that churns food and uses chemicals to help break it down.
  
  

• Small intestine: A long organ where most digestion and absorption of nutrients occurs.
  
  

• Villi: Tiny finger-like structures lining the small intestine that increase surface area for absorption.
  
  

• Pancreas: An organ that releases substances that help digest food.
  
  

• Capillaries: Tiny blood vessels that absorb nutrients and carry them through the bloodstream.