“Fantastic Voyage!”
Aretha Saunders-Phillips
HS130, Section #4
Unit #9 Assignment
Kaplan University
April 1, 2014

Fantastic Voyage

Walter, a 55 year old male has just eaten a hamburger, French fries and a root beer. Our mission is to travel through the gastrointestinal tract as a video reporter and monitor the digestion of Walter’s meal. First we enter through the mouth where food is broken down into smaller molecules by the teeth. The teeth are hard organs found along the anterior and lateral edges of the mouth. Teeth are made up of a bone-like structure called dentin and covered in a enamel layer for hardness. The tongue contains rough papillae, which grips food as it is moved the tongue muscles. The tongue also helps to push food toward the posterior part of the mouth for swallowing. In the mouth there are 3 sets of salivary glands that produce a watery secretion know as saliva. With the assistance of salivary enzymes or saliva the food particles are moistened and are then able for the tongue and other muscles to push the food into the pharynx, which is connected to the posterior end of the mouth. We are now travelling downward through a long muscular tube that extends from the pharynx to the stomach and the food will then enter the esophagus. The pharynx serves two different functions in the digestive system; it has a flap of tissue called the epiglottis that acts as a switch to route food to the esophagus and air to the larynx (enchantedlearning.com, 2001). The food has now entered the esophagus and we are experiencing a series of rhythmic, wave like muscle movements, called peristalsis. This movement forces food from the throat to the stomach. We have entered the stomach which is a large muscular sac located on the left side of the abdominal cavity, just inferior to the diaphragm. The stomach is lined with a mucous membrane which contains glands that secrete gastric juices. The stomach is a storage area for food until the body has had time to digest the food properly. While in the stomach gastric acid is secreted in three phases: cephalic, gastric, and intestinal. The cephalic phase is activated by the smell and taste of food and swallowing. The gastric phase is activated by the chemical effects of food and the distention of the stomach. The intestinal phase blocks the effect of the cephalic and gastric phases. After the stomach receives the bolus, peristalsis begins and the gastric juices and bolus are mixed together to become chyme. Now from the stomach we travel to the duodenum, which is the first part of the small intestine. The duodenum continues to breakdown food, while peristalsis continues. The jejunum and ileum are responsible for absorption of nutrients into the blood stream. The superior mesenteric artery supplies the small intestine with blood. The superior mesenteric artery and pancreatic duodenal artery run between layers of mesentery membrane that connects the intestines with the wall of the abdominal cavity. The blood from the intestine is returned by the superior mesenteric vein along with the splenic vein, which forms the portal vein, which drains into the liver. The division of the portal vein creates the hepatic portal, which is two large branches, each going to one of the major lobes of the liver. The hepatic portal vein arises from the gut, enters the substance of the liver behind not only the bile but also the hepatic artery. The superior mesenteric vein receives blood from the small intestines, two-thirds of the large intestine, and the stomach (http://en.wikipedia.org/wiki/Hepatic_portal_vein, 2014). The superior mesenteric vein drains the distal third of the large intestine, including the descending colon, the sigmoid colon, and the rectum. The splenic vein is formed from branches from the spleen, pancreas, and portions of the stomach, and the inferior mesenteric vein. The hepatic portal vein delivers materials from these digestive and circulatory organs directly to the liver for processing. The processed blood that came from the hepatic artery exits the liver via the right, left, and middle hepatic veins, and flows into the inferior vena cava (CNX Anatomy and Physiology, 2013). The inferior vena cava receives blood from the liver via a series of hepatic veins which drain the central vein. It is now time for waste materials to be filtered and excreted from the body. The renal artery enters into the kidney at the level of first lumbar vertebra just below the superior mesenteric artery. As it enters the kidney it divides into branches: first segmental arteries, which divide into 2 or 3 lobar arteries, then divides again into interlobar arteries and they divide again into arcuate arteries, which leads into the interlobar artery, and forms the afferent arterioles. The kidneys main function is to maintain homeostasis in the body. By doing so the kidney must regulate water volume, blood volume, and interstitial fluid volume. The kidney also regulates normal blood pressure, regulates body pH, excretion of toxic substances, excretion of excess substances, and reabsorption of required substances that were removed in the glomerulus. We began our filtration in the nephron, where pressure is pushing fluid and solutes through the microscopic holes of the glomerular capillaries. As we travel to a portion of the nephron called the Loop of Henle we find various materials, liquid waste, and water (http://en.wikipedia.org/wiki/Kidney, 2014). Water re-absorption, along with certain materials, such as calcium and potassium takes place in the Loop of Henle. The large cells and proteins stay in the blood and the plasma is taken to the nearest proximal convoluted tubule. The proximal convoluted tubule runs down into the medulla into the Loop of Henle and then back to the farthest distal convoluted tubule to join with other tubules. As the kidney filters blood, they also create urine, which collects in the kidneys’ pelvis. The kidney pelvis is funnel-shaped structures that drain down tubes called ureters to the bladder. The ureters, urinary bladder, and urethra form the urinary tract and works to drain urine from the kidneys, store it, and then release it during urination. There is a 10 to 12 inch long pair of tubes that run on the left and right sides of the body called the ureters that carry urine from the kidneys to the urinary bladder. The ends of the ureters extend just slightly into the urinary bladder and are sealed at the point of entry to the bladder by ureterovesical valves. The valves prevent urine from flowing back towards the kidneys (innerbody.com, 2013). Urine is now being stored in a sac-like hollow organ called the urinary bladder, located along the body’s midline at the inferior end of the pelvis. The urinary bladder has walls that are stretchable and can hold anywhere from 600 to 800 milliliters of urine. After urine is stored in the urinary bladder it passes through a tube that extends from the bladder to the exterior of the body called the urethra. The urine flow through the urethra is controlled by the internal and external urethral sphincter muscles. The internal urethral sphincter is made of smooth muscle and opens involuntarily when the bladder reaches a certain set of distention. The internal sphincter gives you that urge to urinate. The external urethral sphincter is made of skeletal muscle and may be opened to allow urine to pass through the urethra or may be held closed to delay urination.

References

Barron, J. (2014). “The Baseline of Health Foundation”, Retrieved from: http://jonbarron.org/article/physiology-urinary-system#.Uzs3-RzbPSh
Circulatory Pathways, (2014), retrieved from http://cnx.org/content/m46646/latest/
The Digestive Process, (2001), retrieved from http://www.enchantedlearning.com/subjects/anatomy/digestive/
Hepatic Portal Vein, (2014), retrieved from http://en.wikipedia.org/wiki/Hepatic_portal_vein
Kidney, (2014), retrieved from: http://en.wikipedia.org/wiki/Kidney
Urinary System Anatomy, (2013), retrieved from: http://www.innerbody.com/image/urinov.html