Question

Describe three ways that the body maintains the acid-base balance of body fluids. (pages \(220-22\) )

Short answer

The body maintains acid-base balance of body fluids through three primary mechanisms: 1) the bicarbonate buffering system, which involves the reaction of bicarbonate ions with hydrogen ions to regulate pH levels; 2) the respiratory system, which controls carbon dioxide levels in the body, thereby regulating carbonic acid concentrations; and 3) the renal system, where the kidneys excrete or retain hydrogen and bicarbonate ions to regulate the pH of body fluids. These mechanisms work together to ensure that the pH levels remain in the normal range and prevent fluctuations.

Step-by-step solution

1. Bicarbonate Buffering System

The bicarbonate buffering system is the primary chemical buffering system in the body that maintains the acid-base balance of body fluids. This system consists of a weak acid, carbonic acid (H2CO3), and its conjugate base, bicarbonate (HCO3-). When there’s an excess of hydrogen ions (H+) in the body, the bicarbonate ion will act as a base and combine with the hydrogen ions to form carbonic acid. Conversely, if there's a lack of hydrogen ions, the carbonic acid will dissociate into bicarbonate ions and hydrogen ions. This reaction ensures that the pH levels remain in the normal range.

2. Respiratory System

The respiratory system plays a crucial role in regulating the acid-base balance by controlling the levels of carbon dioxide (CO2) in the body. CO2 is a byproduct of cellular metabolism, and when dissolved in blood plasma, it forms carbonic acid, which contributes to the acidity of body fluids. When there is an increase in acidity (more H+ ions), the respiratory system increases the rate and depth of breathing, which results in the elimination of more CO2 from the body. This reduces the levels of carbonic acid and brings the pH of body fluids back to the normal range. Similarly, when the body fluids are too alkaline (less H+ ions), the respiratory system decreases the rate and depth of breathing to retain more CO2, increasing the levels of carbonic acid and thus restoring the acid-base balance.

3. Renal System

The renal system, which includes the kidneys, also plays a significant role in maintaining the acid-base balance of body fluids. The kidneys are responsible for excreting or retaining hydrogen ions (H+) and bicarbonate ions (HCO3-) to regulate the pH levels in the body. When the body fluids are too acidic, the kidneys excrete more hydrogen ions into the urine and reabsorb bicarbonate ions back into the bloodstream, thereby increasing the pH of body fluids. Conversely, when the body fluids are too alkaline, the kidneys excrete more bicarbonate ions into the urine and reabsorb hydrogen ions, lowering the pH of body fluids. The renal system's ability to regulate the acid-base balance is slower than the respiratory system but provides a more stable and long-term solution to maintaining the balance in body fluids.