Welcome to my first post on the Foundations of Health. I am starting the new year with this new series to start diving into some good nutrition information. And when it comes to foundations of health, I am more and more convinced that digestion is the key to overall health. Eating real, whole foods and properly digesting it provides literally every raw material your body uses to perform every single function from walking to digestion to releasing hormones and firing neurons. None of those things can happen without a steady stream of properly digested vitamins, minerals, proteins, fats, and carbohydrates. Our bodies have the incredible ability to take the food that we eat, break it down into usable pieces that then become us. Every piece of every cell of your body once existed outside of your body. The root of this incredible process is digestion, so let's take a look at how digestion is supposed to work.
Digestion starts in the brain. The sight and smell of food signals to the brain that we're going to be eating soon. The brain then alerts the digestive system to get ready to receive food. Our salivary glands release saliva into the mouth, and our stomaches churn out gastric juices. This is why you can walk by a bakery or restaurant, smell the food wafting out and immediately get hungry.
Once you take a bite, digestion continues in the mouth. Both mechanical (chewing) and chemical digestion starts here. Chewing the food breaks it down into smaller pieces that can more easily be broken down further along in digestion. It also combines the food with saliva that contains salivary amylase that begins chemically breaking down carbohydrates into more simple sugars. Once the chewed food and saliva combine, it's called a "bolus." When you swallow, the bolus travels down the esophagus, through the cardiac sphincter (aka the lower esophageal sphincter or LES) and into the stomach.
In the stomach, both chemical and mechanical digestion continues. The churning action of the stomach coats the bolus with stomach acid (this acidified bolus is called chyme). This stomach acid helps unbind minerals, and begins protein digestion. Stomach acid also acts as a barrier into the rest of the body by killing off harmful bacteria and parasites before they can get into the intestines and wreak havoc. These bacteria and parasites are then digested just like any other proteins.
Once the food is properly acidified, the pyloric valve will open so that the chyme can move on to the duodenum, which is the very beginning of the small intestine. The duodenum is where digestion is really completed. The gall bladder squeezes bile into the duodenum to emulsify fats so they can be absorbed or further broken down into fatty acids. The pancreas sends in enzymes to further break down proteins into amino acids. The pancreas also sends sodium bicarbonate to the duodenum to bring the pH of the chyme closer neutral. If the chyme travelled down the intestines fully acidified it would burn up the fragile intestinal membrane. Now that the food has been broken down to it's most basic parts- fatty acids, amino acids, and sugar, it is now ready to be absorbed in the small intestine.
The small intestine is lined with tiny hair-like villi and microvilli. These villi are providing extra surface area within the small intestine to absorb as much of the nutrients from the food as possible. They are absorbed through the intestinal wall, and then sent to the blood or lymph system for circulation around the body. The intestines are a selectively permeable membrane. They allow specific substances through, but keep others out. When all of the absorption of nutrients is complete, the chyme moves on to it's final destination: the large intestine.
Since nearly all the nutrients in the body have been absorbed, we're mostly left with waste and water. The large intestine's job is to absorb some of that water back into the body, as well as anything else useful, like some hormones. Finally, all that is left is excreted out as feces.
This process may seem fairly familiar or straight forward, but remember this is an ideal. There are a lot of places along the way that things can go wrong, all the way from the brain to the large intestine, that result in digestive discomfort or even disease. Stay tuned, in the next month I'll be posting a follow-up about digestive issues, and some easy things to try to address some of them on your own.
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