A Journey through the Digestive, Circulatory and Urinary Systems
My Fantastic Voyage: A Journey through the Digestive, Circulatory and Urinary Systems
My journey begins with the ingestion of a cheeseburger, fries, and root beer by a 55 year old man. I begin my trip in the gastrointestinal tract. While in the mouth, the food is masticated by the teeth and combined with saliva to moisten the bolus and begin digestion. Salivary amylase begins the breakdown of starches into smaller sugars and salivary lipase begins breaking down the fats (“Saliva,” 2013). We are then swallowed and peristalsis moves us down the esophagus towards the stomach (University of Leicester, 2001).
Upon arrival in the stomach, we are bathed in gastric acids. We first enter at the cardia. When we look up, we can see the fundus which is a reservoir for digestive gases. The body of the stomach is responsible for secreting hydrochloric acid and pepsinogen which helps liquefy the food. The pylorus is our last stop before entering the small intestine. The pylorus is responsible for secreting mucous, pepsinogen and gastrin. The stomach is very important in that it liquefies the food, controls how fast the food moves into the small intestine, and begins primary food digestion (University of Leicester, 2001).
Now we enter the small intestine. The small intestine is comprised of three regions, the duodenum, the jejunum, and the ilium. In the duodenum, the highly acidified food from the stomach is neutralized by an alkaline secretion from the Brunner’s glands (University of Leicester, 2001). The breakdown of carbohydrates into simple sugars occurs here with the help of enzymes from the liver and pancreas. Fats are also broken down here into fatty acids by the addition of an enzyme called lipase from the pancreas. The next section of the small intestine is called the jejunum. It has a highly folded lining with projections called villi for the efficient absorption of monosaccharides, fatty acids, and amino acids (the building blocks of proteins). Water, vitamins, and minerals are also small enough to be absorbed into the blood stream here (“Jejunum,” 2013). We then enter the ilium which is responsible for absorbing bile salts and the vitamin B12. It also has a large surface area, thanks to villi, to absorb whatever nutrients were not absorbed in the jejunum. The epithelial cells here secrete the enzymes carbohydrase and protease to further breakdown carbohydrates and proteins, respectively. It is here our submarine is absorbed into the bloodstream through the mucuosa and we enter the Superior Mesenteric Vein (SMV) (“Ileum, 2013). In the SMV, we first pass the right ureter, then the inferior vena cava, the inferior duodenum, and pancreas. It is here that the SMV joins the lineal vein to make the portal vein (“The Portal System of Veins, n.d.). Just as we reach the liver, we enter the hepatic portal vein. We are absorbed into the liver sinusoids so that the liver can remove any toxins. Initial absorption of nutrients occurs here, then the blood is drained back into the portal vein (“Hepatic Portal Vein,” 2013).
We are now on our way to the kidneys. The kidneys are responsible for the removal of waste products and water from the blood stream forming a fluid known as urine for removal from the body. The renal arteries deliver the newly oxygenated blood from the heart and lungs to the kidneys. Within the kidneys, we enter the renal which branch off into interlobular arteries which that then feed into afferent arterioles. These supply the glomeruli which will filter the blood for water and waste before removing it from the body as urine.
We leave our journey as we are concentrated in the urine and removed from the body via urine. Our path out of the human body is through the urinary bladder and urethra. The primary product from the kidneys is urea, waste products mostly from protein metabolism. Combined with water, it makes urine which travels from the kidneys through the ureter into the bladder, where it is stored until we urinate. When the nerves in in the bladder are triggered by pressure, we urinate and the urine travels through the urethra outside our body (“Your Urinary System and How It Works,” 2012).
So what has our journey taught us? There are multiple systems responsible for maintaining a delicate balance in the human body. This is known as homeostasis, or the regulation of internal conditions in response to environmental conditions within certain boundaries such as temperature, pH, water balance and electrolytes, blood pressure, temperature, and respiration. Each of the systems we travelled through today play a role in maintaining homeostasis in the human body. But, we cannot ignore the fact that the nervous and endocrine systems regulate homeostasis (Bailey, n.d.).
In order for biological reactions to occur efficiently, they need to occur within a narrow tolerance of environmental conditions. Within the digestive system, the rate of digestion and absorption is dictated by how fast the food moves through the digestive system. We did not mention the role of the large intestine in our journey, but it is very important in the absorption of water and minerals. The digestive system also plays a strong role in filtering the blood for toxins in the liver. Within the circulatory system, the provision of energy from the digestive process is very important, but also the amount of water in the system will affect blood pressure. In the urinary system, fluid balance is ultimately regulated as well as the removal of the byproducts of digestion. We have had a fantastic journey through the human body and we now appreciate how amazing all the integrated systems function.
References
Alters, S. & Alters, B. (2006), Biology: Understanding Life, Hobokon, NJ: John Wiley & Sons, Inc.
Bailey, R. (n.d.). In About.com Biology. Retrieved from http://biology.about.com/od/biologydictionary/g/homeostasis.htm
Hepatic Portal Vein. (2013, February 21 ). In Wikipedia, The Free Encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Hepatic_portal_vein
Ilium. (2013, February 21 ). In Wikipedia, The Free Encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Jejunum
Jejunum. (2013, February 21 ). In Wikipedia, The Free Encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Jejunum
Kidney. (2013, February 27). In Wikipedia, The Free Encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Kidneys
Saliva. (2013, February 26). In Wikipedia, The Free Encyclopedia. Retrieved from http://en.wikipedia.org/w/index.php?title=Saliva&oldid=540422197
The Portal System of Veins. (n.d.). In Yahoo Education. Retrieved from http://education.yahoo.com/reference/gray/subjects/subject/174#p682
