Pathophysiology

Pathophysiology Study Guide

©2018 of 131 by the tubular cells such that hydrogen is secreted, and in turn, bicarbonate is generated. Finally, the mechanism of ammoniagenesis helps in the formation of NH 3 buffer. Compensatory Mechanisms Compensatory responses are the defense mechanism that helps to mitigate or minimize the effect of the imbalance that disturbs the level of pH in the blood. It should be noted that compensatory responses do not directly normalize the pH levels, but correct the underlying reasons that cause the disorder. It is characterized by the renal or respiratory response that alters the ratio of PCO 2 /HCO 3 - in order to minimize the change in H+. The compensatory response for metabolic disorders involves a change in alveolar ventilation, while that in respiratory disorders involves a fast response because of cell buffering and slower response due to renal adaptation. In metabolic acidosis, the initial chemical change is a fall in HC0 3 -. The compensatory mechanism in this case would be hyperventilation and the compensatory response would be a decrease in PCO 2 . In contrast, with metabolic alkalosis, there is an increase in HCO 3 -; therefore, the mechanism would be hypoventilation due to the compensatory response of an increase in the PCO 2 . In respiratory acidosis, the initial chemical change is characterized by a rise in PCO 2 and the compensatory rise in HCO 3 -. It should be noted that the compensatory mechanism in acute and chronic respiratory acidosis would now be different. For acute cases, the mechanism would be intracellular buffering, while for chronic cases, the mechanismwould be the generation of new HCO 3 - as the excretion of ammonium rises. Similarly, in the case of respiratory alkalosis, the initial chemical change would be a fall in PCO 2 and the compensatory response would be a fall in HCO 3 -. For acute cases, the mechanism would be intracellular buffering, while in the case of chronic respiratory alkalosis, the compensatory mechanism would be a fall in the reabsorption of HCO3- as the excretion of ammonium decreases. 5.4 Acute Renal Failure When the kidney becomes incapable of filtering waste substances from the blood it is known as acute kidney failure. Due to losing the filtering capability, the blood accumulates a very high level of water, which disturbs the chemical composition of the blood. The main causes of acute renal failure include impaired blood flow to the kidneys, damage to the kidneys, and the blockage of urine in the kidneys. Symptoms of acute renal failure include a fall in urine output; swelling in the legs, ankles, and feet due to the retention of fluid; drowsiness; shortness of breath; fatigue; state of confusion; nausea; coma; seizures; and a rise in pain and pressure in the chest. Achieve Page 81