Due to the fact that I’ve been squished under a pile of work and studying, I haven’t been able to post as much biology things as I wanted. Now that it’s Friday, I have a little time to do so. So, I found myself wondering what I should post about, and then it hit me, while I was eating a dumping. After all, this also works as a great review tool for me.

The Digestive system is primarily broken down into three parts: Ingestion, Absorption and Elimination. 

Ingestion, of course, begins in the mouth. As we know, we chew and cut the food we ingest with the help of our teeth. That act is called mastication. By breaking the food down into smaller pieces, its surface area is increased. Once that is done, saliva coats the food. Saliva contains salivary amylase which breaks down amylose and starch, killing some the bacteria and acting as a buffer to raise the pH of the food in oder to make it less acidic. In turn, our tongues shape the food into a ball, called the bolus, and pushes it into our throat, also known as the pharynx. By peristalsis, the pharynx contracts, moving the bolus downwards. This course eventually becomes the esophagus which also performs peristalsis. Once the bolus reaches a certain area before entering the stomach, it passes through the cardiac sphincter which acts like a gateway into the stomach. Its main function is to prevent the stomach acid from reaching the esophagus.

The Digestion phase begins once the bolus reaches the stomach where it mixes with gastric acid, also known as stomach acid, that has a pH of 2. In addition, the stomach produces pepsinogen which turns into pepsin in an acidic environment. It is strong enough to kill bacteria, break down proteins, and also powerful enough to burn through the stomach’s walls. How is gastric acid contained in the stomach? Well, the stomach lining constantly secretes mucus for protection, but they still undergo mitosis to regenerate cells that die off. After the adventure in the stomach, the bolus is now called acid chyme. The contents pass through the pyloric sphincter—yet another gateway— into the small intestine. The first portion of the small intestine is the duodenum in which acid chyme mixes with pancreatic acid, a buffer that counters the acidity of the acid chyme, and bile, produced by the liver and stored by the gal-bladder. As the acid chyme and its mixture travel through the rest of the small intestine, the broken down nutrients are absorbed by its villi, allowing the blood vessels that surround the small intestine to absorb the nutrients. These blood vessel converge into the hepatic portal that connects to the liver where most of the nutrients are stored into and the rest are given to the body.

Once the contents reach the large intestine, Absorption begins. As you recall, food was mixed with gastric acid, bile and pancreatic juice, most of which is really made out of water. If our bodies would let all of that pass through and straight out of us, then we would undergo massive water loss. Therefore, in order to avoid dehydration, the large intestine reabsorbs the water that was used, making the contents more solid. The large intestine is also home to E. Coli—the good kind, yes there are good ones— that take some of the waste material and produce vitamins that benefit us. However, they also produce methane… which is farting gas. Overall, it’s a mutualistic relationship where both organisms benefit. By the end of the absorption stage, we have ourselves a good, solid piece of feces. (:

-Nicole Acnam