Compensatory mechanisms of acid-base balance: respiratory acidosis and alkalosis and metabolic acidosis and alkalosis

Compensatory mechanisms for Metabolic AcidosisThe body regulates the acidity of the blood by four buffering mechanisms:

• Bicarbonate buffering system

• Intracellular buffering system

• Respiratory compensation

• Renal compensation

Bicarbonate buffering systemThe bicarbonate buffering system is an

important buffer system in the acid-base homeostasis.

In this system, carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3), which in turn rapidly dissociates to form hydrogen ions and bicarbonate (HCO3- )

The carbon dioxide - carbonic acid equilibrium is catalyzed by the enzyme carbonic anhydrase

Intracellular bufferingby absorption of hydrogen atoms

by various molecules, including proteins, phosphates and carbonate in bone.

Respiratory Compensation of Metabolic Acidosis

is a mechanism by which plasma pH can be altered by varying the respiratory rate. It is faster than renal compensation, but has less ability to restore normal values

In the case of Metabolic Acidosis chemoreceptors sense a deranged acid-base system, and there is increased breathing

Renal Compensation of Metabolic Acidosisthe kidney produces and excretes

ammonium (NH4+) and monophosphate, generating bicarbonate in the process while clearing acid

Compensatory mechanisms for Metabolic Alkalosis2 Buffering mechanisms :

Renal compensationRespiratory compensation

Respiratory compensation - occurs mainly in the lungs, which retain CO2 through slower breathing, or hypoventilation (respiratory compensation). CO2 is then consumed toward the formation of the carbonic acid intermediate, thus decreasing pH.

The decrease in [H+] suppresses the peripheral chemoreceptors, which are sensitive to pH. But, because respiration slows, there's an increase in PCO2 which would cause an offset of the depression because of the action of the central chemoreceptors which are sensitive to the partial pressure of CO2[citation needed] in the cerebral spinal fluid. So, because of the central chemoreceptors, respiration rate would be increased.Renal compensation - consists of increased

excretion of HCO3- (bicarbonate), as the filtered load of HCO3- exceeds the ability of the renal tubule to reabsorb it.

Compensatory Mechanisms of Respiratory AcidosisIn acute respiratory acidosis,

compensation occurs in 2 steps :1. The initial response in cellular

buffering that occurs over minutes to hours. Cellular buffering elevates plasma bicarbonate only slightly

2. The second step is renal compensation that occurs over 3-5 days. With renal compensation, renal excretion of carbon is acid is increased and bicarbonate reabsorption is increased.

Compensatory Mechanisms of Respiratory Acidosis

Compensatory Mechanisms of Respiratory AlkalosisCompensation in an Acute Respiratory

Alkalosis :

Changes in the physicochemical equilibrium occur due to the lowered pCO2 and this results in a slight decrease in HCO3-. There is insufficient time for the kidneys to respond so this is the only change in an acute respiratory alkalosis. The buffering is predominantly by protein and occurs intracellularly; this alters the equilibrium position of the bicarbonate system.

Compensatory Mechanisms of Respiratory Alkalosis

Compensation in a Chronic Respiratory Alkalosis :

Renal loss of bicarbonate causes a further fall in plasma bicarbonate (in addition to the acute drop due to the physicochemical effect and protein buffering).

Thanks for your ATTENTION !!!