This question was answered on Tue 10, May 2011 11:33am by Dr Smita Sarwan

Routes through kidneys, blood stream

    
Asked by dwright63 (Female ) on Tue 10, May 2011 09:24am
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I know this is alot but I really need the help with this You have been swallowed by a 55 year old man eating a hamburger, french fries and a root beer. 1. Pilot your sub through the gastrointestinal tract to monitor the digestion of his meal. Describe all major structures you pass by or through, just like a tour guide would do. Describe what happens to the meal during the digestion process. Once you arrive at the distal ileum, go through the mucosal membrane and enter the bloodstream via the Superior Mesenteric Vein. 2. Now in the bloodstream, you are to go to the left kidney Rules of the Road: A. You may never go the wrong way down a “one-way street” B. You are not allowed to “create” new roads C. You may choose any possible route Trace your path from the superior mesenteric vein to the left renal artery, via the hepatic portal vein, heart and lungs. Once again, describe all major structures you pass by or through (but you don’t need to indicate every “side road”). 3. Once you’ve arrived at the kidney, enter the nearest nephron by crossing the glomerular membrane into Bowman’s capsule. Describe the structures you see, and narrate what happens as you travel through the urinary tract, until you leave the body via the urethra. 4. Based on your first-hand observations, wrap up your report by explaining the integration of the body systems in maintaining homeostasis. You must include at least the circulatory, digestive and urinary systems in your explanation.

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Answer by Dr Smita Sarwan  on Tue 10, May 2011 11:33am:

Hi, Welcome to the forum and thanks for posting. The food described by you has carbohydrates, proteins, fats etc. Usually the the process of all is little different. The carbohydrates are composed of chains of simple sugars. In mouth the amylase breaks the longest molecule of glucose (polysaccharide) into smaller molecules (oligosaccharides). No digestion of carbohydrates occurs in stomach. The remaining carbohydrates then pass to small intestine and the molecules which are not broken are broken here by pancreatic amylase. These are then broken down further to small molecules and then eventually get absorbed in blood through membranes. The food is absorbed and the veins from ileum drain eventually into superior mesenteric vein. The superior mesenteric vein then combines with splenic vein to form hepatic portal vein. The portal venous system in liver delivers blood to capillary system that is hepatic sinusoids of liver. The blood then enters the inferior vena cava, right atrium, right ventricle and then pulmonary artery and then lungs. The blood from lungs comes to left atrium by pulmonary vein and then to aorta via left ventricle. The blood from aorta then goes to abdominal aorta. Then the blood goes into the superior mesenteric artery and left renal artery. The blood then enters the kidney via glomerular membrane in the nephrons. The blood trickles from bowman's capsule to renal tubule, that is proximal convoluted tubule, loop of henley, distal convoluted tubule and then into collecting duct system. The blood from cortex is passed to medulla of kidney. The urine thus formed is collected via ureter. The urine from ureter then passes to urinary bladder and leaves the body from urethra. Hope it helps. Take care and keep posting.

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Comment by Dr Bhupinder K, MD on Tue 10, May 2011 11:36am:
Hello, Thanks for posting on the forum. I will try explaining the routes in two different ways as the circulatory system has been very well explained by Dr Smita Sarwan. The two different ways are gthe gastrointestinal pathway, and the urinary pathway. So starting with the digestive system, digestion begins in the mouth where food is acted upon by saliva and enzymes like amylase. The flow of saliva is set in motion by a brain reflex that sets in when we see of smell food. Amylase breaks down some of the carbohydrates (starches and sugars) in the food in the mouth itself and by the act of chewing food is broken down into small bolus. From the mouth, the food moves into moves the food into the throat or pharynx which is a common pipe for air and food. It divides into two: the food pipe and trachea and the epiglottis separates the two so that food mistakenly does not enter the windpipe or trachea. From the pharynx, food travels down a muscular tube in the chest called the oesophagus which is also called the food pipe. There are a number of muscular contractions called peristalsis which propels the bolus of food forward. At the lower end of esophagus, there is an esophageal spincter which acts as a gateway which allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the esophagus. The stomach acts like a mixer grinder where the food churns and mixes with acids and enzymes like pepsin converting it into small digestible pieces. It leaves the stomach in the form of chime (a thick gravy like liquid) and enters the duodenum. At the lower end of stomach also there is another spincter which does not allow food to turn back once it enters duodenum. Duodenum is the first part of small intestine and the other parts are jejunum and ileum (the terminal part). Here the lining of the small intestine has many finger like projections called villi through which nutrients can be absorbed into the body. The small intestine is also in close proximity to the liver, gall bladder and pancreas which although are not directly related to the digestion but are important in secreting enzymes for digestion of food. Liver produces bile that helps the body absorb fat. Bile is stored in the gallbladder which acts as a storehouse until it is needed. The pancreas produces enzymes that help digest proteins, fats, and carbohydrates. Here in small intestine, maximum absorption of food occurs and then it passes into the large intestine which comprises mostly undigested food (and some water). At the junction of the small and large intestine there is a small valve which also acts as a gatecheck to avoid any food from moving back. The large intestine is made up of three parts: cecum, colon and rectum. Cecum is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine and it has a finger like small pouch called appendix which is a vestigial organ and does not help in digestion. From the cecum, food moves into first the ascending colon then transverse colon and then the descending colon by regular peristaltic movements. Bacteria in the colon help to digest the remaining food products. Ultimately it reaches the rectum where feces are stored until they exit the body through the anus. You can have a further reading from the following site for reference (http://leavingbio.net/Human%20Nutrition/H uman%20Nutrition.htm ). Now coming to the urinary system, after the body has absorbed the nutrients and water, waste products are left behind in the bowel and in the blood. These waste products reach the kidneys through the blood vessels and systemic circulation. Urea is produced when foods containing protein are broken down in the body. Urea is carried in the bloodstream to the kidney. This urea is captured by the kidneys from the blood through tiny filtering units called nephrons which act just like a sieve. Here urea along with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney. From the kidneys, urine travels down two thin tubes called ureters to the bladder which is a balloon like organ. The bladder stores urine until it if full and then it expands and sends impulses to the brain through autonomic nervous system. The bladder has circular muscles which prevents urine from leaking. Signals from the brain cause the bladder muscles to tighten and thus squeezing urine out of the bladder. The digestive system works in syngery with the circulatory system to get the absorbed nutrients distributed through your body and thus helps in the growth of the body. I hope this helps. Take care and regards.

Comment by Dominique on Sun 12, Jun 2011 12:19pm:
How do you get from the distal ileum, go through the mucosal membrane and enter the bloodstream via the Superior Mesenteric Vein. How exactly does that work?

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