C34+acid+base+balance+marking+2007.doc

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Department
Biological Sciences
Course
BIOC34H3
Professor
Stephen Reid
Semester
Winter

Description
1 BGYC34 (2007) PhysioEx Lab 10 Acid-Base Balance Marking Scheme Part 1 Complete PhysioEx lab #10. Hand-in all of the pages associated with the lab. Note that there are 9 activities to be completed. You DO NOT need to hand in the histology review supplement. There are 10 questions in part 1 for which marks are assigned. Convert the mark out of 10 to a mark out of 5. Add the mark out of 5 to the mark out of 8 from part 2. The final mark is out of 13. Activity 1: Normal Breathing At 20 seconds, pH = 7.38 or 7.39 or 7.40 or 7.41 or 7.42 At 40 seconds, pH = 7.38 or 7.39 or 7.40 or 7.41 or 7.42 At 60 seconds, pH = 7.38 or 7.39 or 7.40 or 7.41 or 7.42 Note: During any ONE run the pH remains constant. It may be at any one of the above levels but it never change during a single run. Did the pH level of the blood change at all during normal breathing? If so, how? No, the pH level of the blood does not change (during any single run) during normal breathing. Was the pH level always within the normal range for the human body? Yes, the pH level remained within the normal range (7.38 to 7.42) during normal breathing. Did the PCO 2 level change during the course of normal breathing? If so, how? No, the PCO 2level remained constant (40 mmHg) during normal breathing. Activity 2a: Hyperventilation – Run 1 At 20 seconds, pH = approximately 7.45 At 40 seconds, pH = approximately 7.54 At 60 seconds, pH = approximately 7.67 2 Did the pH level of the blood change at all during this run? If so, how? Yes, the pH level of the blood increased over time. Was the pH level always within the normal range for the human body? No, the pH level was not in the normal range for the human body. It increased above normal values. If not when was the pH value outside of the normal range and what acid-base imbalance did this pH value indicate? The pH value began to rise above the normal range between 10 and 20 seconds. This is a respiratory alkalosis. (1 MARK) Did the P CO 2 level change during the course of this run? If so, how? Yes, the PCO 2 level progressively decreased over time (during the hyperventilation). If you observed an acid-base imbalance during this run, how would you expect the renal system to compensate for this condition? You would expect the renal system to compensate for the respiratory alkalosis by - + decreasing HCO re3bsorption and decreasing H ion secretion. (1 MARK) How did the hyperventilation trace differ from the trace for normal breathing? Did the tidal volumes change? During hyperventilation, tidal volume was markedly increased and there was small increase in breathing frequency. What might cause a person to hyperventilate? Two of the major causes of hyperventilation are anxiety and fever. Some drugs (such as cocaine) will also induce hyperventilation. Activity 2b: Hyperventilation – Run 2 What happened to the trace after the 20- second mark when you stopped the hyperventilation? Did the breathing return to normal immediately? Explain your observation. After the period of hyperventilation and the return to normal breathing there was approximately one normal breath before breathing stopped for a few (around ten) 3 seconds. This occurred because P CO 2was low enough to shut off breathing due to the removal of the CO s2imulus from the central and peripheral chemoreceptors. (1 MARK) Activity 3: Rebreathing At 20 seconds, pH = approximately 7.35 At 40 seconds, pH = approximately 7.30 At 60 seconds, pH = approximately 7.25 Did the pH level of the blood change at all during this run? If so, how? Yes, blood pH decreased over time. Was the pH level always within the normal range for the human body? No, the pH level was not always within the normal range; it was lower. If not when was the pH value outside of the normal range and what acid-base imbalance did this pH value indicate? The pH value began to fall out of the normal range at about 20-25 seconds. This was a respiratory acidosis. (1 MARK) Did the P CO 2 level change during the course of this run? If so, how? Yes, the PCO 2 level increased over the course of this run. If you observed an acid-base imbalance during this run, how would you expect the renal system to compensate for this condition? In order to compensate for a respiratory acidosis, the kidney would increase the rate of HCO r3absorption and increase the rate of H ion secretion. (1 MARK) How did the rebreathing trace differ from the trace for normal breathing? Did the tidal volumes change? The rebreathing trace showed greater levels of breathing compared to normal. Tidal volume was elevated as was breathing frequency (albeit the tidal volume change was more obvious than the frequency change). Give examples of respiratory problems that would result in pH and P CO 2 patterns similar to what you observed during rebreathing. Lung disease or airway obstruction could lead to the retention of CO 2hich would increase PCO 2 and decrease pH. 4 Activity 4: Renal Response to Normal Acid-Base Balance At normal P CO 2and pH levels, what level of H was present in the urine? + The [H ]in the urine was normal. There is no quantitative answer to be given. - What level of [HCO ] w3s present in the urine? The [HCO ] in the urine was normal. There is no quantitative answer to be given. 3 Why does the blood pH change as the P CO 2 changes? This question seems out of place. As P CO 2 increases, blood pH decreases because CO is 2 being hydrated to a proton and bicarbonate ion. Activity 5: Renal Response to Respiratory Alkalosis + What level of [H ] was present in the urine at each of these P CO 2pH levels? + At a P CO 2level of 35 mmHg, urine [H ] was normal. As P CO was lowered to 30 and 20 mmHg, urine [H ] was lowered (the kidney was 2 retaining protons). - What level of [HCO ] w3s present in the urine at each of these P CO 2/pH levels? At a P CO 2level of 35 mmHg, urine [HCO ] wa3 normal. As P CO 2was lowered to 30 and 20 mmHg, urine [HCO ] was i3creased (the kidney is getting rid of bicarbonate). Recall that it may take hours or even days for the renal system to respond to disruptions in acid-base balance. Assuming that enough time has passed for the renal system to fully compensate for respiratory alkalosis, would you expect P CO 2 levels to increase or decrease? Would you expect blood pH levels to increase or decrease? The kidney can fully compensate for the pH changes (i.e., bring arterial pH back to normal) but P CO 2 (and HCO ) 3evels will remain low until the respiratory disturbance (alkalosis) is removed. Blood P CO levels would remain at the low level induced by the 2 respiratory alkalosis. The renal compensation would not change this. (1 MARK) 5 Recall our discussion on renal compensation for respiratory disorders that occurred in lecture 20.See the slides on renal compensation for a respiratory alkalosis and the note that a new steady state P CO 2level is achieved. Recall your activities in the first experiment on respiratory acidosis or alkalosis. Which type of breathing resulted in P CO 2 levels closest to the ones we experimented with in this activity – normal breathing, hyperventilation or Rebreathing? The reduced P CO 2levels resemble those observed during hyperventilation which, of course, would induce a respiratory alkalosis. Explain why this type of breathing resulted in alkalosis. Hyperventilation causes an increase in CO ex2retion. Since CO is hy2rated to produce a proton and a bicarbonate ion, less CO i2 the blood means less hydrogen ions and therefore an increase in blood pH. Activity 6: Renal Response to Respiratory Acidosis What level of [H ] was present in the urine at each of these P CO 2pH levels? + As P CO 2was raised to lowered to 60, 75 and 90 mmHg, urine [H ] was elevated (the kidney was secreting protons). What level of [HCO ] w3s present in the urine at each of these P CO 2/pH levels? - As P CO 2was raised to 60, 75 and 90 mmHg, urine [HCO ] was3lowered (the kidney was retaining bicarbonate). Recall that it may take hours or even days for the renal system to respond to disruptions in acid-base balance. Assuming that enough time has passed for the renal system to fully compensate for respiratory acidosis, would you expect P CO 2 levels to increase or decrease? Would you expect blood pH levels to increase or decrease? Ultimately the kidney can compensate for changes in blood pH and restore pH to normal. However, the kidney cannot restore P CO 2 and HCO le3els to normal. Both P CO 2and - HCO le3els remain elevated until the respiratory acidosis ceases. (1 MARK) Note, see the slides on renal compensation for a respiratory acidosis. The renal compensation occurs along a P CO 2 isobar so PCO 2 does not change during the renal compensation. A new steady state P CO 2is achieved that is higher than normal. HCO 3- levels are also higher. 6 Recall your activities in the first experiment on respiratory acidosis or alkalosis. Which type of breathing resulted in P CO 2levels closest to the ones we experimented with in this activity – normal breathing, hyperventilatio
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