Dear journal, 

I was once a living breathing pig. Now I am little more than a couple of vegetables, some grains and a few slices of meat. I sit on a plate waiting to be eaten by a hungry human. I am a happy sandwich, about to go through an exciting journey called the digestive system.

I begin my journey at the mouth, the site of ingestion. I am being eaten. The teeth bite me into small pieces and are responsible for physical digestion. They increase my surface area. Once in the mouth I encounter the tongue. I am being tasted and being moved around in the mouth. Salivary Glands produce saliva,  dome which contains mucus and amylase. The saliva starts chemical digestion which breaks me down. 

Dear journal, 

Once I have finished going through physical digestion, I am swallowed. I am now called a bolus, what a name. I encounter the Pharynx at back of the throat before it splits into the trachea and the esophagus. I see my last light of day as a soft palate moves back to close of the nasopharynx. The trachea moves up under the epiglottis which covers the glottis. This forces me down the esophagus. I am going down the esophagus, and the rhythmic contraction of the esophagus pushes me into the stomach. Once through the esophagus, I approach the Cardiac Sphincter. This is the top of the stomach, which keeps food like me inside the stomach.

Dear journal,

I have arrived at the stomach! The stomach acts as storage for food, like me. The hydrochloric acid in the stomach’s gastric juice is to lower the pH of the stomach. This makes it a harsh environment for any bacteria I may have had on or in me. This hydrochloric acid also lets the enzyme Protease work at the low pH of the stomach. This environment of the stomach is ideal for the breakdown of my proteins to take place! The digestive enzymes are activated, and pepsinogen is changing to pepsin which is breaking down my proteins into peptides. I noticed that a layer of mucus was coating the interior of the stomach! It is preventing the gastric juice from burning the lining of the stomach!  At the bottom of the stomach is the Pyloric Sphincter. It is regulating food like me from leaving the stomach to the duodenum.

Dear journal,

The pyloric sphincter lets me out of the stomach and into the duodenum which is the first 25cm of the small intestines. The pancreas secretes its pancreatic juices into duodenum. The role of sodium bicarbonate in the pancreatic juice is to lower the pH and acidity of the stomach acid when it enters the intestine.  Insulin is released from the beta cells in the pancreas in response to rising glucose in the human’s bloodstream. After I was eaten, my carbohydrates were broken down into glucose and passed into the bloodstream. The pancreas detects this rise in blood glucose and starts to secrete insulin. Insulin works by improving the uptake of glucose from the blood across cell membranes and into the cells of the body, and so takes glucose out of the bloodstream. Once in the cells, the glucose is used as the energy to fuel the cells doing their different jobs or is stored in the liver or muscle cells as glycogen. This results in the glucose level of the blood dropping, which then triggers the pancreas to switch off the release of insulin.

Dear journal,

Digestion of all foods, like me happens in the small intestine. Absorption of my nutrients happens through the villi.  These villi absorb glucose, amino acids, vitamins and minerals. A villi contains a microvilli, capillaries, and lacteals. The functions of the villi and microvilli are to increase my surface area for enabling a faster rate of absorption. The function of the capillaries is to pass nutrients (glucose and amino acids) through the villi by diffusion. The circulating blood then takes these nutrients away. The lacteal does a similar role as the capillary however, it absorbs emulsified fats.

Dear journal,

I am still in the duodenum, and the gall bladder has started to secrete bile into the duodenum. . The purpose of this bile is to emulsify my fats and increase the surface area of my fats. The liver is in charge of many things like producing and excretes bile to dissolve fat and eats up my bacteria and old cells. The liver also aids in breaking down and storing my nutrients. As I leave the small intestine I catch a glimpse of a small projection on the large intestine. It is the appendix! I wonder what it is for….  

Dear journal, 

Once all my nutrients and fats have been absorbed and emulsified, I arrive at the large intestine and the colon. This is where my final absorption of water and the storage of my last non-digestible remains end up. Some nice E. coli are here to help digest and produce some vitamins and amino acids.

Dear journal,

My journey is almost coming to an end as I reach the rectum, the last 20 cm of the large intestine. Anaerobic bacteria in the colon takes up space and nutrients and, in that way, limit the ability of pathogenic bacteria in the colon from proliferating (if there's no food, the raw materials needed for them to multiply aren't there and if there is no space for them to grow, they simply can't grow and expand their numbers). Here, what is left of me is compacted into feces. 

Dear journal, 

I just passed the outlet of the digestive tube, the anus.

 I have changed a lot from this journey. The only that is left of me is my non-digestible remains! I have learned a lot of things about the digestive system. 

One of the things that I observed was the importance of the pH level in various regions of the digestive tract. The different pH levels in various regions of the digestive track allow each part of the system to do its function properly. For example, the stomach would not be able to digest and break down food like me if it were not for the high pH, because the enzymes that thrive in high pH levels would not function. The pH in the small intestine must be lowered by pancreatic juices, because the small intestine does not contain the same mucus coating to protect it from the gastric juice’s acidity. I also got to observe many different enzymes do their work. I have included my observations and findings in another journal entry. As well, I was able to witness all of the wonderful things that water does for the human body. I have also included these findings in another journal entry. Both of these things were so important I decided I should dedicate entire sections to explain their role. 

Digestive Enzymes

These are all the digestive enzymes I observed in action on my trip through the digestive system.

-          Salivary amylase – Source gland is salivary glands, they promote the breakdown of carbohydrates in the mouth.  Specifically, starch into maltose.

-          Pancreatic amylase - Source gland is pancreas, works in the small intestine.  It promotes the same reaction as salivary amylase.

-          Proteases (pepsinogen, pepsin, trypsin)

-          Lipase – Splits bond between glycerol and fatty acids.  Source gland is the pancreas, and it works in the small intestine.  It digests fat droplets after they have been emulsified by bile salts.

-          Peptidase – Secreted by the small intestine, it functions as to breakdown protein to amino acids.

-          Maltase – Secreted by the small intestine, it functions as to breakdown maltose into glucose.

-          Nuclease – Splits bond between sugar and phosphate in RNA and DNA, secreted by the pancreas, and acts in the small intestine.

Importance of water in the human body

Water is a very important part of a human's bodily functions. As I travelled through the digestive system, it became apparent how many ways in which water was involved. 

Digestion & Waste Elimination

·         Water is a major component in saliva and of the digestive juices in the stomach. Water keeps the feces moist enough to pass through the alimentary canal. The kidneys also use water to dilute wastes, making them easier to pass from the body. With diseases like diabetes, the kidneys remove excess sugar from the blood and then need to dilute that sugar with extra water in order to pass it from the body.

Metabolism & Respiration

·         Metabolism of food into usable energy is a chemical process that requires a lot of water and oxygen. The body uses water to break down nutrients into their component parts. The lungs use water vapour for osmosis, the transfer of oxygen and carbon dioxide. The air sacs (alveoli) in the lungs have minute amounts of water. As air enters the lungs, the water in the alveoli break the gasses down into their component parts. It is these component parts that pass through the walls of the alveoli into the bloodstream.

Regulation of Body Temperature

·         Water is a major component of blood and sweat. Water has a high specific heat and easily absorbs large amounts of heat. The water in blood regulates body temperature by absorbing the heat from metabolic processes and transferring that heat throughout the body in the circulatory vessels. Blood also cools the body by moving to the surface of the skin, where the outside air cools the blood. The cooled blood then circulates around the body, cooling the body. This is why people with fevers appear flushed. Sweat cools the body through evaporation. The sweat sits on the surface of the skin and as it dries it releases heat. In humid areas, the concentration of water in the air prevents sweat from evaporating off the skin.

Moistening & Lubrication

·         Water moistens mucous membranes, the interior of the lungs, the pleura surrounding the lungs and the membranes surrounding the organs. This layer of moisture allows the tissues to slide over each other, preventing lesions and adhesions. Water is also a major component of synovial fluid, which cushions and lubricates the joints.

Journal conclusion

Dear journal, 

I started out as a sandwich, and now I am just compacted non-digestibles that have been expelled from the human body. The amazing system that was able to transform me is the human digestive system.

I was able to observe and go through all of the different parts. I was processed though physical digestion, swallowing and peristalsis, gastric juices and pancreatic juices. I learned the major functions of the liver and the role of bile in the emulsification of fats. I know the structure of villus and can describe the functions of anaerobic bacteria in the colon. I was also able to witness all of the digestive enzymes in action, and see the importance of water. 

Most of my journey was enjoyable, but the end was shit.