C34+renal+marking+2007.doc

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Department
Biological Sciences
Course
BIOC34H3
Professor
Stephen Reid
Semester
Winter

Description
BGYC34 Fourth Assignment (2007) PhysioEx Lab 9 (Renal System Physiology) Due Date: Wednesday March 14 2007 Part 1 Complete PhysioEx lab #7. Hand-in all of the pages associated with the lab. Note that there are 5 activities to be completed. You DO NOT need to hand in the histology review supplement or the review sheets. (8 marks) Activity 1: Investigating the Effect of Flow Tube Radius on Glomerular Filtration What happens to the glomerular filtration rate as the afferent radius is increased? As the afferent radius increased, glomerular filtration rate increased. Predict the effect of increasing or decreasing the efferent radius on glomerular filtration rate. Increasing the efferent radius would decrease the glomerular filtration pressure and therefore decrease the glomerular filtration rate. Decreasing the efferent radius would increase the glomerular filtration pressure and therefore increase the glomerular filtration rate.(1 mark) Activity 2: Studying the Effect of Pressure on Glomerular Filtration What happened to the glomerular filtration rate as the beaker pressure was increased? Glomerular filtration rate increased as beaker (i.e., blood) pressure was increased. Explain your answer? Increased beaker (blood) pressure leads to an increase in glomerular hydrostatic pressure which is one of the pressures favouring glomerular filtration. (1 mark) Activity 3: Assessing Combined Effects on Glomerular Filtration There appears to be something wrong with this portion of the simulation. This section is supposed to be examining the combined effects of tube radius and pressure on glomerular filtration rate. However, the only manipulation is to close the valve blocking the collecting duct; there is no exercise in which pressure and radius changes are made so that one counteracts the other. Furthermore, once the collecting duct is blocked, glomerular filtration rate is quantified as being zero yet there is still the visual image of filtration occurring at the glomerulus. How does this run compare to the runs in which the valve was open? Although the glomerular pressure remained the same, there was no glomerular filtration or urine formation when the valve was closed. In this situation, the blockage at the end of the collecting duct would presumably lead to an increase in pressure throughout the nephron and into Bowman’s capsule. Since the glomerular filtration rate was zero you can assume that this pressure build-up was sufficient to counter the forces favouring filtration leading to the total lack of glomerular filtration. Expanding on this concept, what might happen to total glomerular filtration and therefore urine production in a human kidney if all of its collecting ducts were totally blocked? If all collecting ducts were blocked you would expect no glomerular filtration or urine production. Would kidney function as a whole be affected if a single nephron was blocked? No. there are millions of nephrons per kidney. Blocking one would have no affect. Would the kidney be functioning if glomerular filtration was zero? Explain. No, if there is no glomerular filtration then there can be no tubular fluid formation and no urine production. (0.5 marks) Explain how the body could increase glomerular filtration rate in a human kidney. In theory, glomerular filtration could be increased by increasing glomerular hydrostatic pressure or reducing Bowman’s capsule hydrostatic pressure or reducing plasma oncotic pressure. In practice glomerular filtration is maintained at a constant level in the face of changes in blood pressure. An increase in glomerular hydrostatic pressure could be caused by an increase in blood pressure, an increase in the diameter of the afferent glomerular arteriole or a decrease in the diameter of the efferent glomerular arteriole. If you increased pressure in the beaker, what other conditions(s) could you adjust to keep the glomerular filtration rate constant? If beaker (blood) pressure increased then glomerular filtration rate could be maintained constant by decreasing the diameter of the afferent arteriole diameter or increasing the diameter of the efferent arteriole. There could also be mesangial cell contraction leading to a decrease in the surface area for filtration (although this isn’t part of this simulation exercise). (0.5 marks) Activity 4: Exploring the Role of the Solute Gradient on Maximum Urine Concentration Achievable What happened to the urine concentration as the gradient concentration was increased? As the concentration gradient of the interstitial fluid increased the urine solute concentration increased. What would be the maximum possible urine concentration if the maximal interstitial solute concentration were 3000 milliosmoles instead of 1200 milliosmoles? The maximum urine concentration would be 3000 mOsm. Urine can be concentrated to a level equal to that in the peritubular (interstitial) fluid at the bottom of the loop of Henle (i.e., in the deep parts of the renal medulla). (1 mark) Activity 5: Studying the Effect of Glucose Carrier Proteins on Glucose Reabsorption What happened to
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