The digestive system is one of the main systems we have in our bodies. It is from this system that we get the vitamins, minerals, and even water we need for survival. We learned the basic steps of this process in class based on the big digestive system we had made with Homer’s “lunch menu”.
It all begins when we first put food in our mouths, or “his mouth”. We learned that the first main step our body performs as part of our digestive system is mechanical digestion, where we break down the food we are eating into smaller pieces by chewing. Salivary glands are already producing saliva even before we begin eating (as we saw in Homer’s picture), and in the saliva we also have Salivary Amylase, which is an enzyme that breaks down starch into smaller substances. This enzyme’s role is already part of the second step of our digestion, which is the chemical digestion. In chemical digestion enzymes (speed up chemical reactions; catalysts) help our bodies break down the big substances of food we eat until they are small enough for our bodies to absorb the nutrients from it. To represent the chemical digestion we used scissors as our enzymes, and cutting the substances with each enzyme (scissors) meant that the enzyme was breaking down the substances. This helped me a lot to actually visualize the enzyme’s role and importance in the digestive system.
So, continuing the process, we saw that still in our mouths, the Salivary Amylase breaks down carbohydrates (starch) from polysaccharides into simpler sugars like disaccharides (maltose) and then to even simpler ones. This chewed, smaller foods, and “new” smaller substances are then moved to our esophagus (when we swallow it) and pushed down to our stomach by the peristalsis. In the stomach we learned that we have HCI, which is an acid that also “facilitates” this breakdown, along with the enzyme Pepsin, which is an enzyme that breaks down proteins. Pepsin then starts to break down the large protein substances in our stomach from polypeptides, to dipeptides and finally to amino acids. After the stomach breaks down as much proteins as the pepsin is able to, all of the broken down food goes out of the stomach on its way to the small intestine.
When the “food” is on its way to the small intestine we saw that a lot of things begin to happen at the same time. The pancreas liberates all of the enzymes it produces in order to finish the digestion process (the pancreas produces all kinds of enzymes needed). It also liberated bicarbonate since the acid HCI from the stomach also moves with the food and the small intestine, along with the rest of the body, is not resistant to the acid as the stomach is. At the same time as the pancreas is acting and doing all of these jobs, the liver is also acting on the food being digested. It liberated bile, produced in its gallbladder, which helps “separate” the big lipids molecules we eat, breaking them into smaller molecules so that later the enzyme is able to act on it. After these 2 organs “finish” contributing to the digestion process the food finally gets to the small intestine.
In the small intestine food is “still” being digested but its also absorbed. We saw in our diagram that this is basically were most of the things happens because we are both digesting and absorbing the most. The small intestine produces a juice that contains several enzymes like proteases, lactase, maltase, sucrase, and lipase. These enzymes finish digesting any “left over” substance that hasn’t been digested in the other organs, transforming it into its simplest forms along with the pancreatic enzymes like trypsin and pancreatic amylase. The nutrients are then turned into the smallest, simplest, substances they can be like monossacharides, amino acids, fatty acids and glycerol and are finally absorbed by the villi structure of the small intestine. The capillary bed structure of the villi increases its surface area and also contains lacteal, which helps digestion of fats and along with its microvilli, allows greater digestion and absorption of the nutrients to the blood vessels ( which are right next to the villi- single celled layer).
Finally we saw that in Homer’s digestive system anything that wasn’t absorbed in the small intestine then moves to the large intestine where water, minerals, and vitamins are absorbed (if they haven’t been absorbed before since they don’t require any digestion), and the waste products along with cellulose, is then excreted from the rectum and anus, finally out of our bodies, finishing the work of our digestive system, and enabling us to start it all over again.
We also learned from the diagram and the notes that the digestive system is one that even though seems to have different steps, actually have its steps connected to each other, interconnecting the whole system as one. We were able to see this clear connection while doing the concept map (as shown below), that connects everything that is related in this system (we even see repeated words for different parts, showing its “similar work”), which at least for me, facilitated my understanding of the concept itself.
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