Home School Life Journal From Preschool to High School

Home School Life Journal ........... Ceramics by Katie Bergenholtz
"Let us strive to make each moment beautiful."
Saint Francis DeSales

The Human Digestive System (Grades 5-8)

We talked this week about what happens to food as it passes through each part of the digestive system. We had already reviewed our study of the digestive system and how food gets ground into small bits and mixes with saliva in the mouth and becomes a soft lump called bolus, 
The muscles in the pharynx contract, squeezing the food so that it moves into the esophagus. The muscles of the esophagus contract and relax to bush the bolus along and into the stomach.
James' (age 14) science notebook page

Stomach Acid and Antacids

In the stomach, the bolus is mixed with gastric juices, which is a mixture of liquids, but one of the most important of these is hydrocloric acid. I wanted to show the boys how antacids work. In order to do this, we made up some red cabbage indicator like we have used before to experiment with acids and bases. Once it was cool, we poured it into a clear mason jar. 

We put 1 teaspoon of toilet bowl cleaner in a glass measuring cup. Not unexpectedly, the solution turns pink/red, indicating that the solution is acidic.
Then we added an antacid tablet. The tablet began bubbling and fizzing as it dissolves. Because the antacid is made up of calcium carbonate and magnesium hydroxide, both bases, it turns purple. It could also have turned blue.

All of the acid has been neutralized. Our stomach holds a lot more acid than this glass held, so if you ingest an antacid tablet because you have extra acid in your stomach, the antacid should neutralize just the extra acid, leaving plenty behind to digest food.

You can then add another teaspoon of toilet bowl cleaner, which turns the solution back to red/blue, because the solution is now acidic again. This can be done back and forth repeatedly with the same results.

Smooth muscles in the stomach relax and contract, churning the bolus with the gastric juice until it is turned into a liquid mush called chyme. Chyme passes into the small intestine.


The Pancreas and The Effect of Sodium Bicarbonate on Stomach Acid

The pancreas makes several digestive juices which are squirted into the small intestine as the chyme passes through the pyloric sphincter. It also produces a base called sodium bicarbonate. 

To demonstrate this, as before, we mixed together toilet bowl cleaner and red cabbage indicator, turning the indicator a red/pink. This represents our chyme as it enters the small intestine.

Next we scooped some baking soda out and added it to the solution in the glass and very quickly the solution turned purple/blue.

One of the products of this neutralization is carbon dioxide, which bubbles up in the glass, and which, if we get too much of it in our system, comes out of us as a burp. Essentially the same thing happens in your small intestine when the chyme, which contains hydrocloric acid, mixes with the sodium bicarbonate from the pancreas.
After that, the digested food continues through the intestine and, along the way, the blood absorbs the digested food so that it can used in different parts of the body. That is why the small intestine is so long. By the time the chyme has passed through the entire small intestine and moves into the large intestine, it is mostly composed of indigestible material. The large intestine's job is to make it so that it easily passes the waste out of the body. In the large intestine are bacteria which digest some of the chyme, consolidating the waste. Vitamin K, folic acid and biotin are also produced by bacteria which live in both the large and small intestine.
Any waste products that make it to this point are now called feces and are expelled out of the body through the anus via the rectum.

Sources and Resources:

  • Exploring Creation with General Science, Jay Wile
  • Exploring Creation with Human Anatomy and Physiology, Fulbright and Ryan


  1. I love this project, what a great idea to use antacids for showing how it works.

  2. Very cool lesson! Your science is always very hands-on!

  3. This is so comprehensive, & also contains a 'potions' element, which my kids always love. Thank you!


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