Physical & Chemical Changes in the Digestive System

Physical & Chemical Changes in the Digestive System
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  • 0:00 Digestive System
  • 1:09 Digestion in the Mouth
  • 2:26 Digestion in the Stomach
  • 3:23 Digestion in the Small…
  • 4:39 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
In this lesson, we'll be learning about the changes that take place in your digestive system when you eat. We'll cover both the physical and chemical changes as they happen in different organs, like your mouth, stomach and small intestine.

Digestive System

Right now, you're probably having a snack and something to drink as you work. Brain food is important! But how does that food actually get from your plate to your brain? The answer is your digestive system, a collection of organs that break down food into smaller components that your cells can use.

There are two main ways that digestion happens: physical and chemical. In physical digestion, your body mechanically breaks down food, grinding or smashing it into smaller pieces. However, during chemical digestion, enzymes, or tiny proteins, alter the structure of the food, which is made up of lots of atoms linked together.

When your body employs chemical digestion, the bonds between certain atoms are broken, liberating smaller molecules to be taken to your cells. Although your digestive system has additional organs that perform crucial functions, like the esophagus for transporting food, the large intestine for absorbing water and the rectum for storing waste, we'll focus on three organs that are also important for the breakdown of food: the mouth, stomach and small intestine.

Digestion in the Mouth

The mouth is the first site of digestion. Even though you might think of the mouth as just a gateway to the rest of the workers in the digestive system, it actually participates in both the mechanical and chemical processes. As you might guess, your teeth head up mechanical digestion. They grind, or macerate, your food into a ball called a bolus, which is transported through the esophagus to the stomach. Your tongue also helps push the food around, forming the bolus.

Now, all that saliva in your mouth isn't just to lubricate the process, it actually contains an enzyme called salivary amylase, which mediates chemical digestion. The salivary amylase breaks down carbohydrates, like the molecules in bread, into individual sugar molecules. Your cells can't take in large carbohydrates, like starch, but they can easily use sugars. So, one goal of the digestive system is to break down large carbohydrates into sugars.

One key characteristic of chemical digestion is that it is more specific than mechanical digestion. Typically, enzymes only work on one substance; for example, salivary amylase only works on carbohydrates. Mechanical digestion, such as maceration, however, will break all food down evenly.

Digestion in the Stomach

From the mouth, the food goes to your stomach. Your stomach is a giant pit of acid, a strong chemical that easily breaks the bonds of any substance. The acid eats away at the bonds in proteins and carbohydrates, forming a soupy liquid of acid and food called chyme. As this is happening, enzymes like pepsin break down proteins, while other enzymes break down carbohydrates.

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