pH measures how acidic or alkaline a substance is, based on hydrogen ion concentration. The human body maintains a tightly regulated physiological pH, essential for various biological processes and ensuring a stable internal environment for cells and organs.
Understanding Physiological pH
The pH scale spans 0 to 14, with 7 as neutral. Values below 7 are acidic, above 7 alkaline. Each whole number change represents a tenfold difference; a pH of 4 is ten times more acidic than a pH of 5.
In human biology, “physiological” refers to conditions optimal for biological functions. Blood pH is typically maintained between 7.35 and 7.45, making it slightly alkaline. Other body fluids have different pH values; stomach acid, for example, ranges from 1.5 to 3.5, suitable for digestion.
The Importance of pH Balance
Maintaining physiological pH is crucial for proper body functioning. This balance directly impacts enzyme activity; enzymes function optimally within specific pH ranges. Deviations can alter their structure, reducing effectiveness or causing denaturation, where they lose their shape and ability to function.
Protein structure is also sensitive to pH changes. Proteins are composed of amino acids, and their interactions are influenced by the surrounding pH. Changes in pH can alter amino acid residues, leading to modifications in protein shape. Higher-level structures that dictate a protein’s function can be severely disrupted, rendering the protein inactive.
pH balance is essential for oxygen transport by hemoglobin. Hemoglobin’s oxygen binding is influenced by pH, a phenomenon known as the Bohr effect. In active tissues, increased carbon dioxide lowers pH, causing hemoglobin to release oxygen. In the lungs, a higher pH promotes oxygen binding for transport.
Body Systems for pH Regulation
The body employs several mechanisms to regulate pH within its narrow physiological range, neutralizing and removing excess acids or bases.
Buffer systems provide the first line of defense against pH shifts. The bicarbonate buffer system, crucial for stabilizing blood pH, involves carbonic acid and bicarbonate ions. These quickly neutralize introduced acids or bases, preventing drastic changes; for instance, bicarbonate ions neutralize hydrogen ions, forming carbonic acid.
The respiratory system plays a significant role in short-term pH regulation by controlling blood carbon dioxide levels. Carbon dioxide forms carbonic acid, affecting blood pH. When blood is too acidic, increased breathing expels more carbon dioxide, raising pH. If blood is too alkaline, breathing slows to retain carbon dioxide, lowering pH.
The renal, or kidney, system provides a long-term and powerful mechanism for pH control. Kidneys regulate blood pH by excreting excess hydrogen ions into the urine and reabsorbing bicarbonate from the urine back into the blood. They reabsorb nearly all filtered bicarbonate, ensuring this important buffer remains in the bloodstream. This dual action allows the kidneys to adjust the body’s acid-base balance over hours to days.
When pH Levels Change
Significant deviation from physiological pH indicates a failure in the body’s homeostatic regulatory mechanisms. These conditions are broadly categorized as acidosis and alkalosis. Acidosis occurs when body fluids become too acidic (pH drops below 7.35), due to excess acid or bicarbonate loss. Alkalosis is when body fluids become too alkaline (pH rises above 7.45), indicating excess base or acid loss. Both can lead to serious health complications if not corrected.