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The body has three ways of maintaining a normal pH range: Chemical buffer systems, respiratory controls and renal mechanisms. First we’ll describe chemical buffers. They act within seconds to help the body control pH. To see how buffers work, let’s see what happens when there is no buffer as in pure water. First we’ll add acid to the water. Notice the large drop in pH, which is typical when acid is added to an unbuffered solution. Most buffers are composed of weak acid and weak base pairs, which are sometimes called conjugate acid/base pairs. The purpose of a buffer is to help the body maintain a relatively constant pH. There are three important buffer systems in the body: The carbonic acid/bicarbonate buffer system, the phosphate buffer system and protein buffers. First, let’s discuss the carbonic acid bicarbonate buffer system. The weak acid is carbonic acid and the weak base is bicarbonate. Let’s add acid to the buffered solution. The hydrogen ion attaches to the weak base, bicarbonate, to form a weak acid, carbonic acid. Because the hydrogen ion attaches and is not free in solution, the pH will not change dramatically. The weak acid that forms will not dissociate into hydrogen ions to any great extent. Now let’s bring it back to pH 7… …and add base to the buffer. The hydroxide pulls a hydrogen ion off of carbonic acid forming water and bicarbonate. Because the hydroxide pulled a hydrogen ion off of the carbonic acid and formed water, the hydroxide did not significantly increase the pH of the solution. As you remember, this is the equation for the carbonic acid bicarbonate buffer. Now let’s expand the equation to see how the entire respiratory system works to regulate pH. Carbonic acid can break down into carbon dioxide and water. Carbon dioxide and water can also combine together to form carbonic acid, which breaks down into bicarbonate and hydrogen ion. Bicarbonate and hydrogen ion can also come together to form carbonic acid, which splits into carbon dioxide and water. While these mechanisms may seem complex, keep in mind that we have discussed only three mechanisms for renal control of acidosis: Conserving or reabsorbing filtered bicarbonate. Generating new bicarbonate ions by the kidney tubule cells, which increases the pH of the plasma and adds new buffering power to the plasma and secreting buffered hydrogen ion into the urine. This eliminates hydrogen ions from the body and increases the pH of the plasma. Metabolic alkalosis is caused by a relative deficit of any acid in the body, except carbonic acid. Metabolic alkalosis can be caused by an excess of base in the body. Ingestion of two much bicarbonate or baking soda would produce an excess of base. Metabolic alkalosis can also be a result of two little acid in the body. Vomiting of stomach contents containing hydrochloric acid would deplete the acid in the body. Metabolic alkalosis can occur when there is too little potassium in extracellular fluid. Hypokalemia causes potassium to come out of cells in exchange for hydrogen ion. Let’s look at an example of how alkalosis occurs. Jose Fuentes has caught the stomach flu that’s been going around the office and is vomiting. As a result of vomiting, Jose is losing a lot of stomach acid. What would you expect to happen to his plasma pH? His pH will rise indicating he is becoming alkalotic from loss of hydrogen ion. As alkalosis progresses, Jose will experience the effects of rising pH on interstitial fluid. Initially nerve cell membranes become irritable and muscle spasms and convulsions may occur. With severe alkalosis, central nervous system depression occurs, and confusion, lethargy, and coma may ensue. Death occurs when the plasma pH reaches about 7.8. Fortunately, Jose only has a 24-hour flu. Respiratory alkalosis is a deficit of carbon dioxide and occurs as a result of hyperventilation. When respirations are excessively deep and rapid, carbonic acid is excreted rapidly from the lungs in the form of carbon dioxide and water. The result is a deficit of both carbon dioxide and carbonic acid. What causes an individual to hyperventilate to the point of carbonic acid deficit? Low levels of oxygen in the plasma may cause hyperventilation. Stimulation of the brain stem such as in the case of meningitis may cause hyperventilation. Head injury may also cause hyperventilation. For Sally however, hyperventilation appears to be caused by severe anxiety over a visit to the dentist.