8.25.20 Lesson #2 Digestion/Brain&Mouth

If I were to ask you where digestion starts, would you say the mouth? Guess what! You’re right! At least partially correct. The most important thing that works in tandem with the mouth is our brain. Yes, our brains are an intricate part of digestion!

Even before we put food in our mouths, the sight and aromas of our meal begin to trigger salivary glands to start producing saliva. Even though saliva is mainly water, a small portion is solutes and in that solute are salivary amylase. Salivary amylase starts the breakdown of carbohydrates. Do you remember the definition of digestion? That’s right! “Digestion is the mechanical and chemical breakdown of food. The goal of digestion is to reduce food molecules so small that the nutrients can be absorbed and used by the cells.”(NTA slides 2019)

So this breakdown of food starts by the brain seeing and smelling that yummy sourdough toast with avocado (because that’s what everyone is eating right now, right?!) and saying, “Oh, that has some carbohydrates in it. I’m going to need lots of salivary amylase to start breaking that down.” Your teeth start masticating (breaking down) the food into smaller bits. Your salivary glands pump out saliva to moisten food to help with swallowing (and that contains the amylase to break down carbs). Hopefully you chew thoroughly enough to break that toast and avocado down into tiny bits and completely mix the saliva with the food.

Next comes swallowing. The tongue pushes the chewed food to the back of your mouth into your pharynx, or top of your throat. Next comes the pharyngeal stage. “During this phase, called the pharyngeal phase, the larynx (voice box) closes tightly and breathing stops to prevent food or liquid from entering the airway and lungs.” (NIH Pub. No. 13-4307 October 2010) At this point, as the food enters your esophagus, the glob of chewed food and saliva is called a ‘bolus.’ The muscles in your esophagus are triggered and within about 3 seconds the bolus has traveled from your mouth all the way to a little trap door at the top of your stomach called the cardiac sphincter (or lower esophageal sphincter, LES). That sphincter opens up just long enough to let that bolus into your stomach and then closes back up to wait for the next bite to arrive.

The food has finally arrived in your stomach, but instead of digestion starting there, today you’ve learned that the process is already well under way! Next week we’ll explore the stomach, a truly incredible organ!