Overview of Acid-Base Regulation

Acid-base balance refers to how the body maintains a balanced pH of body fluids within a narrow range. A balanced pH is essential for optimal cellular functioning; and any disruption in this balance can adversely affect important metabolic processes, such as the function of enzymes within cells, oxygen delivery to the tissues, and medication metabolism.

Alright, so, pH, which means potential of hydrogen, reflects the concentration of hydrogen ions, or H+, in the blood. An acid is a substance that releases H+, and there's an inverse relationship between pH and H+, meaning that when there's more H+, the pH decreases and the blood becomes more acidic; and, when there's less H+, the pH increases, and the blood becomes less acidic. Now, hydrogen ions are continually produced by normal metabolic processes like ketone production from fat metabolism; phosphoric acid from the breakdown of proteins; and lactic acid resulting from aerobic respiration, which can be due to excess exercise or hypoxia.

On the flip side, a base is a substance that accepts hydrogen ions, which neutralizes acid. Bicarbonate or HCO3-, is a base found in plasma, and it plays a crucial role in acid-base balance. When there's more HCO3- the pH increases, and the solution becomes more basic; and when there's less HCO3-, the pH decreases, and the solution becomes less basic.

Okay, so pH is measured on a scale that ranges from 0 to 14, with a pH of 7 being neutral, less than 7 being acidic, and more than 7 being more alkaline. Optimal metabolic functioning occurs when the pH is maintained between a range of 7.35 and 7.45.

Now, the body has three lines of defense that work together to maintain pH within the optimal range. First, there are chemical buffering systems, like the carbonic acid-bicarbonate system, that act immediately by making small adjustments to the pH. When blood becomes too acidic, a condition called acidosis, the excess H+ can combine with HCO3- to form carbonic acid, or H2CO3-, which then forms water, or H2O and carbon dioxide, or CO2. The CO2 is then exhaled by the lungs, increasing the pH. On the other hand, if the blood becomes too basic, a condition called alkalosis, H2CO3- can dissociate into H+ and HCO3-, decreasing the pH.

The lungs are the second line of defense, which respond to shifts in pH by changing the rate and depth of respirations. With acidosis, chemoreceptors in the brain sense a high concentration of H+. This stimulates an increase in respirations, so more CO2 is eliminated from the body, increasing the pH. Alternatively with alkalosis, chemoreceptors sense a low concentration of H+. This stimulates a decrease in respirations, so more CO2 is retained, lowering the pH. This is a quick response, occurring within minutes of an acid-base alteration.

Finally, the third line of defense is the renal system which helps maintain pH by eliminating excess H+ and reabsorbing more HCO3- in an acidotic state or retaining H+ and eliminating excess HCO3- in an alkalotic state. This is a slow response, which can take hours to days.

Alright, as a quick recap.... Acid-base balance refers to the maintenance of a balanced pH between 7.35 and 7.45 to ensure optimal cellular functioning. There are three lines of defense that work together to maintain the pH of body fluids, including chemical buffering, respiratory, and renal systems.