High school

How is the pH scale important for your digestion?

The more I was getting into the inorganic Chemistry, the more I was fascinated by how the reactions I was writing on paper were actually happening inside and around me. I was looking at things with new eyes: for example, every time I was seeing something burning, or just even the smell of burnt, it was reminding me of the exchange of electrons that was taking place between the chemicals involved in that reaction in order to allow the combustion to happen.

This correlation between reactions done on papers and the actual reality around me was incredibly amusing and I have to be thankful to my Chemistry teacher for this. She perfectly understood how to catch the students’ attention and how to show them that Chemistry, and knowledge in general, can be relatable to our everyday lives. Unfortunately, the Italian government did not, and still now, does not give enough money to public schools, therefore we did not have any chemical or biological laboratory to actually play around with chemistry or even do some practical experiments on the topics we studied. But my Chemistry and Biology teacher made always the effort to correlate all the topics and the seemingly pointless exercises we had to do with something more concrete and “touchable”, as it was the case for the pH. 

This was the next big chapter we had to go through in our inorganic Chemistry lessons. pH, that stands for “power of hydrogen”, is a scale that defines the acidity or basicity of a solution and to introduce this new and tricky topic she started talking about our stomach and the relevance of this scale in the digestive process. What left me stunned was that our stomach is actually producing hydrochloric acid during digestion in order to get an acidic environment. Hydrochloric acid is a strong acid with a corrosive effect on human tissues and the ability to damage organs irreversibly. However, this acidic pH is necessary as it acts as a barrier against bacteria that we might ingest along with what we are eating and it also helps digest the food, fostering the enzymes that break down the food molecules and promoting the chemical reactions involved. Without the acidic pH, our digestion, that normally takes around 4 hours, would require hundreds of years!

Thus, today as a “science related fact” I would like to talk about our stomach and sodium bicarbonate, also known as baking soda, a common antacid used to neutralise stomach acidity and relieve an upset stomach after a huge lunch or dinner (a pretty common problem in Italy during holidays or festivities!).

“Science Related Fact” (SRF):

As I already mentioned above, our stomach contains cells that release gastric acid: this consists mainly of hydrochloric acid, in order to acidify its environment to a pH of 1 to 2 during digestion (see picture below). This acid environment is used by the digestive enzymes  in the stomach that will breakdown the food we just ate and it also acts as a barrier against microorganisms to prevent infections. These same cells also produce mucus, that creates a barrier to prevent gastric acid from damaging the stomach. Right after leaving the stomach, the hydrochloric acid is neutralised in the first section of the small intestine by sodium bicarbonate. This neutralisation blocks the gastric enzymes that have their optima in the acid range of pH.

“The pH Scale”. This scale describes the acidity or basicity of a solution. A neutral solution has a pH of 7: if pH < 7, the solution is acid; on the other hand, if pH > 7, the solution is basic. The picture shows some examples of acid and basic solutions we see in our everyday life. The stomach acid and the baking soda are highlighted.
Modified from Poster de vecttori diseñado por Brgfx – Freepik.com

The neutralisation reaction between hydrochloric acid and sodium bicarbonate rapidly equilibrates the pH with carbon dioxide and water, leading to their dissolution in the blood and finally their exhalation through the lungs. However, when there is an excessive production of acids in the stomach, these gastric acids can potentially exit the stomach and damage the esophagus, as it is the case when we have a large and heavy meal or when there are pathologies like acid reflux.

A quick and easy solution, useful at least to relieve the acid indigestion after heavy meals, is helping the esophagus and stomach to neutralise the gastric acid with sodium bicarbonate. Sodium bicarbonate, also known as baking soda, is a white, fine powder that has a slightly salty taste. It has multiple uses: for example, it is used in baking as a leavening agent, but it is also used in pest control or pyrotechnics. Nonetheless, when sodium bicarbonate is mixed with water it can act as an antacid, helping the one that our body is already producing, in order to neutralise gastric acid and relieve heartburn, indigestion or an upset stomach after large meals.

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