Question

1.Explain how carbonic acid and bicarbonate are formed in the blood and the functions they serve.

2. Define the terms acidosis and alkalosis, and explain how they relate to hypoventilation and hyperventilation.

3. Explain how ventilation is adjusted to help maintain acid-base balance.

Answer 1

1. The carbon dioxide which is released from the cellular metabolism is transported into the capillary blood surrounding the cells. This carbon dioxide reacts with water to form carbonic acid which is later converted into bicarbonates.

CO2 + H2O --> H2CO3

H2CO3 --> H+ + HCO3-

Functions of bicarbonate in the body:

- Bicarbonate is the main buffering system of the body. It helps in regulating the pH of the blood and helps in maintaining the acid base balance in the blood. It neutralizes the excess of acid present in the blood.

- Bicarbonates also neutralizes the acid in the stomach after the gastric phase of digestion to prevent the damage to the gastric mucosa.

- Bicarbonates are also secreted by the pancreas which helps in controlling the acidity of the duodenum.

2. The normal blood pH is between 7.35 - 7.45

Acidosis is defined as increase in the acid level of the blood which decreases the pH to less than 7.35

Alkalosis is defined as increase in the level of bases in the blood which increases to pH to more than 7.45

Kidneys and lungs regulate the levels of acids and alkalis (bases) in the body by controlling the level of carbon dioxide and bicarbonate ions.

Acidosis and alkalosis can be both metabolic (when the kidneys are primarily involved) and respiratory ( when the lungs are primarily involved).

During acidosis, there is excess of hydrogen ions and reduced bicarbonates in the body. The body tries to compensate for this acidosis by exhaling out more carbon dioxide from the lungs by increasing the ventilation rate. Thus, more carbon dioxide is lost through the lungs by hyperventilation thereby reducing the level of acids in the body.

During alkalosis, the body has excess of bicarbonates and reduced amount of hydrogen ions. The body tries to compensate for this by decreasing the rate of ventilation thereby preventing the loss of carbon dioxide from lungs. This carbon dioxide compensates for the alkalosis by creating compensatory acidosis. Thus, in alkalosis, there is hypoventilation to decrease the amount of carbon dioxide lost from the lungs which adds to the acidity of the blood thereby compensating for the alkalosis.

3. Acid base balance is maintained by regulating the functions of the lungs and kidneys.

Lungs maintain the acid base balance by controlling the amount of carbon dioxide exhaled out by regulating the rate of ventilation depending upon the acid base level of the body.

Whenever there is excess of acids in the body (acidosis), the lungs start to exhale out more carbon dioxide by increasing the rate of ventilation. As carbon dioxide generates the hydrogen ions responsible for the acidity, increased loss of carbon dioxide through the lungs by hyperventilation causes increase in the blood pH which means compensating for the acidosis.

Whenever there is alkalosis ( increased pH to more than 7.45 ), there is decreased hydrogen ions and increased bicarbonates in the blood. The body tries to compensate for this alkalosis by decreasing the rate of ventilation thereby decreasing the amount of carbon dioxide lost through the lungs. As more carbon dioxide is now retained, it compensates for the increased bicarbonates or decreased hydrogen ion levels. Thus, alkalosis is compensated by decreasing the rate of ventilation (decreasing the amount of carbon dioxide lost)