Thursday, April 21, 2011

Your thirst and hunger centers tell you that you are dehydrated and hungry. You decide a cold water and chicken wings will satisfy such desires. You need to reach for your frosty beverage on the counter directly in front of you. Your starting point should be anatomical position. Trace the path of the water from the mouth to the urethra, listing the path in as much detail as possible. Be very specific and very detailed. Your answer should include both the digestive and renal systems.

The first step in the pathway of the water from the mouth to the urethra is the ingestion of the water, which happens in the mouth. After swallowing, the water goes down the pharynx and esophagus, to reach the stomach where it is mixed with the food and gastric juices. It then passes into the small intestine where it is absorbed. Diffusion of the water through the cell membrane occurs through osmosis. The water will diffuse into capillary blood, reaching the blood stream, traveling to the kidneys through the renal arteries. Here the optimal amount of water will be determined, and the excess will be discharged into urine. In the kidneys, nephrons will first perform glomerular filtration, during which blood pressure forces the water and solutes in the blood plasma through the wall of the glomerular capillaries, forming glomerular filtrate. As the filtered fluid flows through the renal tubules and collecting ducts, tubular reabsorption occurs. During this process, most of the filtered water returns into the blood stream. Tubular secretion also occurs, helping to eliminate waste and the excess of water, that is removed from the blood and transported into the fluid in the renal tubules and collecting ducts into the renal pelvis This water is now part of urine and will drain into ureters, travel into the urinary bladder to be stored in there until its volume exceeds 200 to 400mL. When this happens, pressure increases and micturition reflex is triggered, which will relax the urethral sphincter. Urine is expelled into the urethra through the process of micturition, or urination. 

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