SGD: Concept of Compensation

At SGD a student asked questions about the nature of compensation:

1. What is the meaning of compensation?
2. What are the types of compensation?
3. Why is the opposite of a condition taken as the compensation?
4. Why is there 2 phases for compensation, acute and chronic phases?
5. Which conditions have 2 phases for compensation?

There are 4 simple acid-base disorders: respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis. 

Respiratory acidosis has a 2-phase compensatory mechanism - acute and chronic. Respiratory alkalosis has a 2-phase compensatory mechanism - acute and chronic. In respiratory conditions, the compensation is two-phase - acute and chronic. The acute phase involves correction by blood buffers and the chronic phase involves the kidneys. 

In respiratory acidosis, the chronic compensation involves mechanisms to conserve and increase the bicarbonate levels (this resembles metabolic alkalosis), and occurs by two means - regeneration of bicarbonate and reabsorption of bicarbonate.

In respiratory alkalosis, the chronic compensation involves mechanisms to reduce the levels of bicarbonate and to increase acids in the blood. The chronic compensatory phase involves excretion of bicarbonate and conservation/regeneration of acids.

Metabolic acidosis has a single phase compensation. Metabolic alkalosis has a single phase compensation. In metabolic conditions, the compensation is single phase. 

In metabolic acidosis, there is excess acids in the blood and the blood pH drops. The compensation in metabolic acidosis is to breathe fast (hyperventilate), which resembles the mechanism for respiratory alkalosis.

In metabolic alkalosis, there is loss of acids and excess bicarbonate exists in blood. The compensation in metabolic alkalosis is to breathe slowly (hypoventilate) or breathe into a paper bag and breathe the same expired air from the paper bag.