BIOL 2420 Lecture Notes - Lecture 14: Lactic Acidosis, Respiratory Acidosis, Metabolic Acidosis
26 Apr 2018
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Unit 8 – Lecture 14
Metabolic Acidosis
- a disturbance of mass balance that occurs when the dietary and metabolic input of H+
exceeds H+ excretion
o metabolic causes of acidosis include lactic acidosis
▪ result of anaerobic metabolism, and ketoacidosis = comes from excessive
breakdown of fats or certain amino acids
o metabolic pathway that produces ketoacids is associated with type 1 diabetes
mellitus and with low-carb diets
▪ ex: atkins diet
- ingested substances that cause metabolic acidosis include methanol, aspirin, and
ethylene glycol (antifreeze)
- metabolic acidosis is expressed by the following equation:
o hydrogen ion concentration increases because of the H+ contributed by the
metabolic acids
o increase shifts the equilibrium represented in the equation to the left = increase
in CO2 levels and using up the HCO3- buffer
- metabolic acidosis can also occur if the body loses HCO3-
o most common cause of bicarbonate loss is diarrhea, during which HCO3- is lost
from the intestines
o pancreas produces HCO3- from CO2 and H2O by a mechanism similar to the renal
mechanism illustrated in figure 20.16
▪ H+ made at the same time is released into the blood
▪ Normally the HCO3- is released into the small intestine, then reabsorbed
into the blood, buffering H+
▪ If a person is experiencing diarrhea, HCO3- is not reabsorbed, and a state
of acidosis may result
- Whether HCO3- concentration is elevated or decreased is an important criterion for
distinguishing metabolic acidosis from respiratory acidosis
- Unless the individual also has lung disease, respiratory compensation takes place almost
instantaneously
o Both elevated CO2 and elevated H+ stimulate ventilation through the pathways
described earlier
o This means that PCO3 decreases to normal or even below-normal levels due to
hyperventilation
- Uncompensated metabolic acidosis is rarely seen clinically
o A common sign of metabolic acidosis is hyperventilation, evidence of respiratory
compensation occurring in response to acidosis
- The renal compensations (discussed for respiratory acidosis also take place in metabolic
acidosis)
o Secretion of H+ and reabsorption of HCO3-
o Take several days to reach full effectiveness
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Document Summary
If a person is experiencing diarrhea, hco3- is not reabsorbed, and a state of acidosis may result. Whether hco3- concentration is elevated or decreased is an important criterion for distinguishing metabolic acidosis from respiratory acidosis. Uncompensated metabolic acidosis is rarely seen clinically: a common sign of metabolic acidosis is hyperventilation, evidence of respiratory compensation occurring in response to acidosis. The renal compensations (discussed for respiratory acidosis also take place in metabolic acidosis: secretion of h+ and reabsorption of hco3, take several days to reach full effectiveness, not usually seen in recent-onset disturbances. States of alkalosis are much less common than acidotic conditions. Occurs as a result of hyperventilation: alveolar ventilation increases without a matching increase in metabolic co2 production. Consequently, plasma pco2 falls, and alkalosis results when the equation shifts to the left: decrease in co2 shifts the equilibrium to the left, and both plasma h+ and plasma. Hco3- decrease: low plasma hco3- levels in alkalosis indicate a respiratory disorder.
