biol_119_lecture_14_10-5-09

biol_119_lecture_14_10-5-09 - Lecture 14, 10-05-2009 End of...

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Lecture 14, 10-05-2009 End of 44 and then onto 45 Review Session today at 3:30 in Newton 201 .
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The most effective molecule for nitrogenous waste disposal in desert animals would be _____. A. ammonia because it uses less energy to make than uric acid or urea B. urea because it is less toxic than uric acid C. uric acid because it takes less energy to make than urea D. uric acid because it does not require water for excretion E. ammonia because it is the most soluble of all the nitrogen-containing metabolic waste products
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The countercurrent multiplier system in the loop of Henle expends energy in the form of ATP to create a high salt concentration in the medulla This enables the kidney to form concentrated urine The collecting duct, permeable to water and urea but not salt, conducts the filtrate through this salt gradient extracting water from the filtrate by osmosis. Approximately, 50% of the urea leaks out adding to the gradient. Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood
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H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O NaCl NaCl NaCl NaCl NaCl NaCl NaCl 300 300 100 400 600 900 1200 700 400 200 100 Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX H 2 O Urea H 2 O Urea H 2 O Urea H 2 O H 2 O H 2 O H 2 O 1200 1200 900 600 400 300 600 400 300 Osmolarity of interstitial fluid (mosm/L) 300 Figure 44.16
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C. Adaptations of the Vertebrate Kidney to Diverse Environments The form and function of nephrons in various vertebrate classes are related primarily to the requirements for osmoregulation in the animal’s habitat Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in their various habitats. Mammals that excrete the most hyperosmotic urine , such as hopping mice and other desert mammals, have exceptionally long loops of Henle . This maintains steep osmotic gradients, resulting in urine becoming very concentrated. In contrast, beavers, which rarely face problems of dehydration , have nephrons with short loops, resulting in much lower ability to concentrate urine.
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Avian reptiles , like mammals, have kidneys with juxtamedullary nephrons that specialize in conserving water. However, the nephrons of birds have much shorter loops of Henle than do mammalian nephrons. Bird kidneys cannot concentrate urine to the osmolarities achieved by mammalian kidneys. The main water conservation adaptation of birds is use of uric acid as the nitrogen excretion molecule. hyper The kidneys of non-avian reptiles , having only cortical nephrons , produce urine that is, at most, isoosmotic (or hypo)to body fluids. However, the
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biol_119_lecture_14_10-5-09 - Lecture 14, 10-05-2009 End of...

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