Kidney physiology and function: Key concepts and questions

Fundamental reasons for kidney function

1. What is the fundamental reason we need kidneys?

2. How does the glomerulus “autoregulate” the filtration rate locally?

3. What does the body monitor in order to determine electrolyte balance?

4. What happens first in response to fluid loss in the ECF (e.g., dehydration)? What happens next?

5. What is tubular deamination and how can it help correct problems with acid/base balance?

6. What feature of oogenesis might contribute to the steep increase in birth defects seen in mothers aged 35 and older?

7. Why is acidosis more common than alkalosis?

8. What would happen to someone who had a congenital disorder that caused them to lack juxtamedullary nephrons and why?

9. How does inhibin exert negative feedback on spermatogenesis without causing large changes in testosterone levels?

10. Kidney dialysis fluid contains no urea or creatinine. Why is this? Why is the concentration of glucose in dialysis fluid 125 mg/dl (normal blood glucose is around 90 - 100 mg/dl)? Essay questions: You will answer five of the following nine questions

11. (Everyone answers this one.) In your own words, describe the events that occur in countercurrent multiplication in the Loop of Henle. Describe what happens in each limb of the loop and what histological features of each portion contribute to their respective functions. Why is it called countercurrent multiplication? Besides water and ion reabsorption, what other critical function does the loop of Henle serve in juxtameduallary nephrons? What would be the effect if the ion pumps in the loop were disabled? What properties does the blood in the vasa recta have that are different from blood elsewhere in
the body and why is this important? Finally, explain how the diuretics called “loop diuretics” work. Why are they such powerful diuretics? For what conditions (that we have discussed) might they be prescribed? What acid/base balance problem can result from their use and why?

12. Which specific acid/base balance problem is the most common? Why is it the most common? What is the primary clinical sign of this condition? How can you distinguish between acute and compensated forms of this condition? What are the ways that the renal and respiratory systems compensate for this condition? How might you treat someone with this condition? Explain what other acid/base problem tends to occur as a secondary effect of this condition and why. How could you use the anion gap to show the source of this secondary effect?

Local autoregulation of kidney filtration rates

13. Blockage of the urinary tract tends to cause decreased GFR (glomerular filtration rates), while nephritis and glomerular damage tend to increase filtration rates. Explain these results based on the net filtration equation for the kidney that relates HPg, HPc, OPg, and OPc. What effect would dehydration have on GFR and why? How would the kidney respond to this? Be sure to include what, if anything, would happen on the local, hormonal, and autonomic levels of control in response to dehydration. How would this be different in someone who was taking ACE inhibitors for high blood pressure? What would happen to the GFR in someone who has protein deficiency?

14. Explain how aldosterone and ADH act on the DCT and collecting duct. How does their presence affect the amount of water, sodium, and potassium reabsorbed? How do these two hormones contribute to: 1) fluid balance and 2) electrolyte balance? Which of these hormones is secreted in response to small changes in sodium concentration? What would happen to your fluid balance if the collecting duct became impermeable to urea and why? What would happen to fluid balance if you have chronic renal failure? What about if you have a disorder that prevents you from releasing renin?

15. The administration of a certain type of diuretics that block sodium reabsorption can cause hyperkalemia and acidosis. Explain how this happens based on the secretion processes that occur in the DCT and collecting duct. How does the body attempt to correct hyperkalemia? What about acidosis? How would the carbonic anhydrase buffer system try to deal with the problem? What type of acidosis is this? How would the respiratory system compensate? Finally, how could a doctor solve these problems without causing additional water retention (presumably, the patient is on this medication for a reason)?

16. Explain how buffer systems work in the blood and in the urine. Give an example of a buffer system that works in the plasma and a different buffer system that works in the urine. Why are these buffers necessary? That is, why is it so important to buffer the blood pH? What about the urine pH? What are the general limitations of buffers? Why doesn’t HCl work as a buffer? How does each of these systems respond to 1) elevated H+ concentration and 2) decreased H+ concentration? How do these systems react to high
protein/low carbohydrate diets? To starvation?

17. Explain the changes that occur in the kidneys and urine of someone with untreated diabetes mellitus. How does the kidney respond to such metabolic changes? How does the  respiratory system respond? How does the carbonic acid/bicarbonate buffer system help this situation? What do you think leads to the high frequency of kidney problems in diabetics? What factor or factors in the glomerular filtration equation is/are responsible for the change in filtration rate in diabetic kidney disease? You must answer at least one of the following two questions:

18. Men and women differ greatly in the way they make gametes. Compare and contrast male and female gametogenesis on the bases of: overall timing of the process (when it starts, stops, etc.), timing of the meiotic divisions, number of functional cells produced, size and content of the gametes, numbers of gametes produced (per day and in the long term), contribution to the zygote, and reproductive lifespan. Explain the hormonal control of spermatogenesis. Why is it important for inhibin to act on only FSH and not LH?

19. Explain the hormonal regulation of the ovarian and uterine cycles. Outline what hormones trigger which events and when. Explain how and why the two cycles are normally interdependent. What can cause the two cycles to get out of sync? How do modern birth control pills work? What about the “morning after” pill (Plan B)? Finally, how does the so-called “abortion pill” (RU-486) work? Why is it so much harder to make a male birth control pill?
Extra Credit 1. What was your favorite topic we discussed in Biology 242 and why?
Extra Credit 2. Why do you think we evolved to have two kidneys instead of one larger one?