PAL Worksheet Week 9 Problem Set 1 TUBULAR SEGMENTS 1) On your white board, draw an unfolded nephron and collecting duct: 2) In which segment of the tubule does the majority of reabsorption take place? - Is this portion of the nephron permeable to water? - Does this portion of the nephron have an unlimited number of transporters for the various substances that are reabsorbed back into blood? - What happens to the reabsorption of substance X when all of its transporters are saturated? Where will the remainder of substance X end up? - What is the osmolarity of the filtrate in this portion of the nephron? How can this be if most of the solute reabsorption is taking place here? 3) Which segment of the LOH is permeable to water, but impermeable to solutes? - What happens to the osmolarity of filtrate as it moves through this segment? Please explain: 4) Which segment of the LOH is impermeable to water, but permeable to solutes? - Why does the solute have to be actively transported out of the tubule in this portion of the LOH? - What happens to the osmolarity of filtrate as it moves through this segment? Please explain: - How is this segment related to the osmotic gradient of the renal medulla? 5) In which segment of the nephron/tubules does fine tuning of water and Na+ reabsorption take place? - Which cells are responsible for this fine tuning? - These cells have receptors for which two hormones? 6) Is facultative water reabsorption greater when an individual is hydrated or when an individual is dehydrated? 7) Using a drawing, describe in detail the mechanism by which ADH acts as an anti-diuretic hormone, making sure to use the following words (along with others) in your description: collecting duct, receptor, channel, blood, peritubular capillaries, water, filtrate, reabsorption, excretion, urine volume, urine concentration: