6 - Acids-base Balance
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- What is the difference between a volatile acid and a non-volatile or "fixed" acid?
- A volatile acid is able to be excreted by the lung, whereas a non-volatile acid is usually the product of a metabolic process and must be excreted by the renal system.
- HCO3-/H2CO3 has a pKa of 6.1, while the pH of blood is 7.4. How can this still be a good buffer?
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*it is abundant
*the effective pKa is greater than 6.1 because this is an open system and excess HCO3- can be breathed off - What organ controls the level of PCO2 in the blood? What organ controls [HCO3-] in the blood?
- PCO2 is controlled by the lungs, by increases or decreases in ventilation. [HCO3-] is controlled by the kidneys, by increasing or decreasing excretion.
- Are volatile acids buffered by intracellular or extracellular processes? What about fixed acids?
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*volatile acids - intracellularly
*fixed acids - both - What is normal cellular pH?
- 6.8
- What transporters are likely to be active if a cell becomes acidic?
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*Na+/H+ antiporter (extrudes H+)
*K+/H+ ATPase (extrudes H+) - What transporters are likely to be active if a cell becomes alkaline?
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*Cl-/HCO3- antiporter (extrudes HCO3-)
*Na+/2HCO3- cotransporter (extrudes HCO3- down its gradient) - When salt is absorbed by intestinal cells, two transporters are used. What are these transporters and what is produced outside of the cell as a result of their action?
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*Na+/H+ antiporter
*Cl-/HCO3- antiporter
*CO2 and water produced outside of cell - How is CO2 transported across the membrane?
- It moves freely by diffusion.
- How do renal cells act as a source for buffer?
- They combine water and CO2 to form H+ and HCO3-. H+ is excreted and HCO3-, the buffer, is released into the blood.
- What is the basic problem in respiratory acidosis?
- There is hypoventilation and the lungs fail to excrete CO2 at the same rate it is produced. This leads to an accumulation of CO2 which combines with water to produce bicarbonate and H+.
- What is the basic problem in respiratory alkalosis?
- Hyperventilation leads to hyperexcretion of CO2. Low PaCO2 equates to low H+ and thus a high pH.
- What is the cardinal difference between metabolic acid-base disorders and those of a respiratory nature?
- Respiratory acid-base disorders are always due to a change in PCO2, whereas in metabolic disorders PCO2 remains constant.
- What creates metabolic acidosis? Alkalosis?
- Acidosis is due to the addition of a fixed acid to the blood or removal of a base. Alkalosis is due to the addition of a fixed base to the blood or the loss of an acid.
- How do metabolic systems compensate for a respiratory acidosis? How is PCO2 affected?
- There is increased renal excretion of H+ and secretion of HCO3- into the blood. PCO2 remains constant and at an abnormally high level.
- How do metabolic systems compensate for a respiratory alkalosis?
- Renal excretion of HCO3- is increased; PCO2 remains abnormally low, but pH decreases.
- How can respiratory mechanisms compensate for a metabolic acidosis?
- An increase in ventilation to increase excretion of CO2. This consumes H+ and raises pH. Note that change is enacted by a change in PCO2, characteristic of respiratory compensation.
- How can respiratory mechanisms compensate for a metabolic alkalosis? Why is this not a great mechanism?
- Hypoventilation increases PCO2 in the blood which increases [H+] and lowers pH. This is limited by the O2 demands of the body.
- Name some conditions that might result in a respiratory acidosis.
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*pulmonary fibrosis
*obstructive lung disease
*neural and neuromuscular disorders affecting regulation of ventilation - What are some conditions that might result in respiratory alkalosis?
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*anxiety attack
*acute asthma
*neural disorders
*mechanical over-ventilation - What are some conditions that might cause a metabolic acidosis?
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*overproduction of lactic acid in severe exercise or hypoxemia
*overproduction of keto acids in diabetes or alcoholism
*loss of HCO3- in diarrhea or renal dysfunction - What are some conditions that might cause a metabolic alkalosis?
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*vomiting (loss of a fixed acid)
*overingestion of HCO3-