Question

Outline the physiological/pathological processes which can lead to metabolic acidosis and how the body can offset this condition. In your answer discuss any buffer systems utilised and any compensatory mechanisms?

Answer 1

Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys to excrete excess acids. Metabolic acidosis can lead to acidemia, which is defined as arterial blood pH that is lower than 7.35.Acidemia and acidosis are not mutually exclusive – pH and hydrogen ion concentrations also depend on the coexistence of other acid-base disorders; therefore, pH levels in people with metabolic acidosis can range from low, normal, to high

CKD Stage 4 and 5

Acute metabolic acidosis, lasting from minutes to several days, often occurs during serious illnesses or hospitalizations, and is generally caused when the body produces an excess amount of organic acids (ketoacids or lactic acid). A state of chronic metabolic acidosis, lasting several weeks to years, can be the result of impaired kidney function (Chronic Kidney Disease) and/or bicarbonate wasting. The adverse effects of acute versus chronic metabolic acidosis also differ, with acute metabolic acidosis impacting the cardiovascular system in hospital settings, and chronic metabolic acidosis affecting muscles, bones, kidney and cardiovascular health.

Compensatory mechanisms

Metabolic acidosis is characterized by a low concentration of bicarbonate (HCO−
3), which can happen with increased generation of acids (such as ketoacids or lactic acid), excess loss of HCO−
3 by the kidneys or gastrointestinal tract, or an inability to generate sufficient HCO−
3. Thus demonstrating the importance of maintaining balance between acids and bases in the body for maintaining optimal functioning of organs, tissues and cells.

The body regulates the acidity of the blood by four buffering mechanisms.

Bicarbonate buffering system

Intracellular buffering by absorption of hydrogen atoms by various molecules, including proteins, phosphates and carbonate in bone.

Respiratory compensation. Hyperventilation will cause more carbon dioxide to be removed from the body and thereby decrease pH.

Kidney compensation

BufferEdit

The decreased bicarbonate that distinguishes metabolic acidosis is therefore due to two separate processes: the buffer (from water and carbon dioxide) and additional renal generation. The buffer reactions are:

{H+ + HCO3- <=> H2CO3 <=> CO2 + H2O}

The Henderson-Hasselbalch equation mathematically describes the relationship between blood pH and the components of the bicarbonate buffering system:

Using Henry's law, we can say that [CO
2] = 0.03 × PaCO
2

(PaCO
2 is the pressure of CO
2 in arterial blood)

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