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The primary event is indicated by the double arrows (TT or 00). Note that respiratory acid-base disorders are initiated by an increase or decrease in PCO2, whereas metabolic disorders are initiated by an increase or decrease in HCO3".

The primary event is indicated by the double arrows (TT or 00). Note that respiratory acid-base disorders are initiated by an increase or decrease in PCO2, whereas metabolic disorders are initiated by an increase or decrease in HCO3".

respiratory and metabolic alkalosis, which are discussed in the next section. Note that in respiratory acidosis, there is a reduction in pH, an increase in extracellular fluid H+ concentration, and an increase in Pco2, which is the initial cause of the acidosis. The compensatory response is an increase in plasma HCOf, caused by the addition of new bicarbonate to the extracellular fluid by the kidneys. The rise in HCO3-helps offset the increase in Pco2, thereby returning the plasma pH toward normal.

In metabolic acidosis, there is also a decrease in pH and a rise in extracellular fluid H+ concentration. However, in this case, the primary abnormality is a decrease in plasma HCO3-. The primary compensations include increased ventilation rate, which reduces PCO2, and renal compensation, which, by adding new bicarbonate to the extracellular fluid, helps minimize the initial fall in extracellular HCO3 concentration.

Renal Correction of Alkalosis—Decreased Tubular Secretion of Hydrogen Ions and Increased Excretion of Bicarbonate Ions

The compensatory responses to alkalosis are basically opposite to those that occur in acidosis. In alkalosis, the ratio of HCO3- to CO2 in the extracellular fluid increases, causing a rise in pH (a decrease in H+ concentration), as is evident from the Henderson-Hasselbalch equation.

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Essentials of Human Physiology

Essentials of Human Physiology

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