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Clinical Application

Acid-Base Imbalances

Ordinarily, chemical and physiological buffer systems maintain the hydrogen ion concentration of body fluids within very narrow pH ranges. Abnormal conditions may disturb the acid-base balance. For example, the pH of arterial blood is normally 7.35-7.45. A value below 7.35 produces acidosis (as"i-do'sis). A pH above 7.45 produces alkalosis (al"kah-lo'sis). Such shifts in the pH of body fluids may be life threatening. In fact, a person usually cannot survive if the pH drops to 6.8 or rises to 8.0 for more than a few hours (fig. 21C).

Acidosis results from an accumulation of acids or a loss of bases, both of which cause abnormal increases in the hydrogen ion concentrations of body fluids. Conversely, alkalosis results from a loss of acids or an accumulation of bases accompanied by a decrease in hydrogen ion concentrations (fig. 21D).

The two major types of acidosis are respiratory acidosis and metabolic acidosis. Factors that increase carbon dioxide levels, also increasing the concentration of carbonic acid (the respiratory acid), cause respiratory acidosis. Metabolic acidosis is due to an abnormal accumulation of any other acids in the body fluids or to a loss of bases, including bicarbonate ions. Similarly, the two major types of alkalosis are respiratory alkalosis and metabolic alkalosis. Excessive loss of carbon dioxide and consequent loss of carbonic acid cause respiratory al-kalosis. Metabolic alkalosis is due to excessive loss of hydrogen ions or gain of bases.

Since in respiratory acidosis carbon dioxide accumulates, this can result from factors that hinder pulmonary ventilation (fig. 21E). These include the following:

1. Injury to the respiratory center of the brain stem, decreasing rate and depth of breathing.

2. Obstructions in air passages that interfere with air movement into the alveoli.

3. Diseases that decrease gas exchanges, such as pH of Arterial Blood

Normal pH range pH of Arterial Blood

Normal pH range pH scale I I I I I I I I I I I I I I I 6.8 7.0 7.357.45 7.8 8.0

pH scale I I I I I I I I I I I I I I I 6.8 7.0 7.357.45 7.8 8.0

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