Digestion: A Great Discovery
Lauren Walker
HS130
Unit #9 Assignment
Kaplan University
11/19/13

Good morning everyone!! Are we ready for another exciting trip through the human body?! Today we will be following the food of 55 year old Harold who recently ate a hamburger and French fries and is now washing it down with a nice tall root beer. We will be following his meal through his GI tract and I will tell you all about all the structures that we will see on the way. Once we arrive at the distal ileum, we will make a small change to our route by getting into his blood stream. We will follow the superior mesenteric vein to the renal artery. Once there, we will travel through the heart, lungs and eventually reach his kidney. We will make our way into the urinary tract where we will eventually leave his body by way of his urethra. If we hurry, we can catch a ride on the tail end of it! As long as everyone is ready, let’s go Our journey will begin in Harold’s mouth, where he is chewing the last bite of his hamburger and washing it down with root beer. The clear fluid that you will see mixing with the chewed up bits of food is saliva. Saliva has enzymes that help break down the food for digestion. Next, digestion moves into the pharynx and then further down into the esophagus. Once inside the stomach, which looks like a large sac, you will see a small round muscle, called the sphincter. This keeps Harold’s food (and us) from flowing back up into the esophagus. Now inside the stomach, you will see all of the deep pits in the stomach lining. These produce gastric juice, which is mixed with the food that is constantly being digested. The food eventually turns into chyme and looks like a thick paste so that we can travel through the pyloric sphincter. After passing through the pyloric sphincter, we enter the duodenum. This is the first part of the small intestine, followed by the jejunum and ileum. The duodenum is 25 cm long and has many villi that absorb nutrients. If you look really close between the villi, you will see the glands that are responsible for secretion of alkaline mucus that protects the small intestine from the chymes acid. The villi contain blood capillaries and lymphatic vessel that is used to absorb lipids. In the middle part of the duodenum we come to two openings that are the minor and major duodenal papillae. This is where bile from the liver and pancreatic digestive fluid get put into the duodenum. (Patton & Thibodeau, 2008). Bile is a dark green to brown liquid that contains cholesterol, bile salt and bile pigments, while pancreatic juice contains mainly water and enzymes. Enzymes that can be found in the pancreatic juice are amylase, protease and Lipase as well as sodium bicarbonate. The chyme now enters the jejunum, or the second part of the small intestine, where absorption begins. The jejunum also contains numerous villi and also has many large circular folds that are called plicae circulares. These folds make nutrient absorption easier by increasing the surface area and the majority of nutrients are absorbed here. We will now enter the ileum with the chyme, which is the longest part of the small intestine. Like the other two parts of the small intestine, there are villi, as well as lymphoid tissue which contain large numbers of lymphocytes and generate immune response in case of pathogenic attacks. They chyme will not be broken down into small molecules and some of them get absorbed into the blood through membranes. We will be getting into the veins at this point because the ileum veins drain into the superior mesenteric vein which will get us into Harold’s circulatory system. You can tell that we are in the superior mesenteric vein because of the conjunction with the splenic vein which forms the hepatic portal vein. The hepatic portal vein drains the blood to capillary beds in the liver. We now enter the inferior vena cava and travel towards the right atrium of the heart where deoxygenated blood is moving to the right ventricle by way of the tricuspid valve and then into the pulmonary artery via the pulmonary valve where we will eventually enter the lungs (Patton & Thibodeau, 2008). In the lungs, the blood releases carbon dioxide and receives oxygen. The blood that has been oxygenated in the pulmonary vein reaches the left atrium and gets into the left ventricle by way of the mitral valve. Blood then enters the aorta from the left ventricle and makes its way to the ascending aorta and then reaches the abdominal aorta. The abdominal aorta divides into the left renal artery and we will then enter the kidneys and supplies blood to this area. This is where we enter Harold’s urinary system. In the urinary system, the renal artery separates many times and forms many arterioles. These arterioles deliver blood to a single kidney’s nephron. Nephrons consist of two main structures: the renal tubule and the renal corpuscle. The renal corpuscle is there the process of urine begins. Each renal corpuscle has an epithelial cup and holds a numerous capillaries which make up the glomerulus. The blood in the glomerulus travels to the renal tube and then finally comes to the collecting duct area. The renal corpuscle is also where the filtering process takes place, as well as in the renal tubule. The renal tubule passes from the cortex into the medullary pyramids that are in the kidneys. The papilla of each of these individual pyramids takes the urine into the minor calyx, which empties into the major calyces and then is deposited into the renal pelvis. The renal pelvis then becomes the ureter and eventually goes into the urinary bladder. The bladder is a balloon like organ and stores the urine. The bladder can expand quite a bit until it is full and has circular muscles that prevent urine from leaking out. We are now in Harold’s urine and will be leaving his bladder via a urethra. Our trip is almost over and we will find our way out through the external genitals (Patton & Thibodeau, 2008).

References
Patton, K. Thibodeau, G., (2008). “Structure and Function of the Body.” Mosby Elsevier, St Louis Missouri.
Unknown, Author. (2005). The Digestive System and Urinary Tracts. Retrieved from http://stomaatje.com/digestivesystem_urinarytracts.html