CONTROL MECHANISMS

We refer to the concentration of H⁺ as the body’s pH. The pH is a numeric value (0-14) used to represent the negative logarithm of the number of hydrogen ions present in one (1) liter of a solution, indicating the degree of acidity or alkalinity of the solution. Because pH is a negative logarithm:

	As the H⁺ concentration increases, the pH goes down and the solution becomes more acidic.
	As the H⁺ concentration decreases, the pH goes up and the solution becomes more alkaline.

Text Box: Examples of common pHs

pH Example
0 Hydrochloric acid
1 Stomach acid
3 Vinegar, cola, beer
5 Coffee
6 Urine
6.5 Saliva
7 Neutral
7.4 Blood, arterial
10 Great Salt Lake
11 Household ammonia
13 Oven cleaner
14 Sodium hydroxide(NaOH) A pH of 7.0 indicates neutrality—equal amounts of H⁺ and hydroxyl ions. Under normal circumstances body fluids tend to be somewhat alkaline. Blood pH is maintained within a narrow range of 7.35-7.45.

A sustained pH below 7.0 or above 8.0 is generally considered incompatible with survival. Consequently some mechanism for neutralizing or eliminating the H⁺ is necessary if blood pH is to remain constant and favorable.

A favorable pH is essential to body functions. Without a favorable pH:

1. Structural shapes of proteins and/or protein functions are altered

2. Enzymatic activity is diminished

3. Chemical reactions may cease.

In addition, acidity or alkalinity may lead to changes in blood vessels or cell membranes placing oxygenation of the myocardium, brain or other vital organs in jeopardy. Also, the effectiveness of a variety of pharmacological agents may be altered during times of acid-base imbalance.

To maintain the body’s pH and prevent life-threatening consequences from a sustained imbalance, several control mechanisms—known as buffers—act to minimize changes. An acid-base buffer is a solution of chemical compounds that prevent marked changes in the H⁺ concentration when either an acid or a base is added to the solution.

Text Box: Memory Jogger:
In the premature or sick newborn these mechanisms (buffers) may be blunted or insufficient placing him at risk for life-threatening imbalances These buffers include:

a. Chemical buffers (carbonic acid, bicarbonate, proteins, phosphates)

b. Physiologic buffers (lungs & kidneys)

c. Biologic buffers (blood and cellular activity)

Let’s look at each of these buffer systems.