The pH scale measures acidity or alkalinity from 0 to 14, with 7 being neutral. For the human body, the pH of arterial blood is maintained within a narrow, slightly alkaline window of 7.35 to 7.45. This precise acid-base balance is standard for all human physiology, regardless of gender. Nearly every biochemical reaction, from enzyme function to oxygen transport, depends on this regulation. Even a minor deviation outside of this range can severely affect organ systems. The body constantly works to neutralize acids produced by normal metabolism, preventing the pH level from becoming imbalanced.
How the Body Maintains pH Balance
The body employs three primary systems to ensure blood pH remains stable. The fastest-acting defense mechanism involves chemical buffer systems present in the blood and cells. Buffers, such as the bicarbonate system, immediately react to any influx of acid or base by binding to or releasing hydrogen ions, minimizing pH change.
The respiratory system provides the next layer of regulation, offering a rapid response to pH shifts. Carbon dioxide (CO2), a waste product of cellular metabolism, acts as a volatile acid when it combines with water to form carbonic acid. The lungs quickly adjust the rate and depth of breathing to either expel more CO2 (to raise pH) or retain more CO2 (to lower pH).
The third regulatory mechanism is controlled by the kidneys. This system is the slowest to act, taking hours to days to fully engage, but it is the most powerful. The kidneys precisely manage the excretion of non-volatile acids, such as phosphoric and sulfuric acids, into the urine. They also reabsorb or generate new bicarbonate ions, a primary buffer, to restore the body’s alkaline reserves.
Understanding Acidosis and Alkalosis
When the body’s regulatory systems are overwhelmed, the systemic pH shifts into imbalance. Acidosis occurs when the blood pH drops below 7.35, indicating an excess of acid or a deficiency of base. Acidosis is classified as either respiratory, stemming from problems with CO2 removal by the lungs, or metabolic, arising from issues with acid production or base handling by the kidneys.
Common symptoms of acidosis include fatigue, headache, and confusion, which can progress to lethargy as the condition worsens. The body may attempt to compensate by increasing the rate and depth of breathing, a pattern known as Kussmaul respiration, in an effort to blow off more CO2 and raise the blood pH. If left untreated, severe acidosis can lead to shock, coma, and death.
Conversely, alkalosis occurs when the blood pH rises above 7.45, indicating too much base or too little acid. Alkalosis is divided into respiratory alkalosis, caused by excessive CO2 expulsion from the lungs, and metabolic alkalosis, resulting from the loss of acid or the gain of bicarbonate.
Alkalosis symptoms often manifest as neuromuscular excitability. Patients may experience lightheadedness, numbness or tingling sensations, particularly around the mouth and extremities, and muscle cramping or twitching. Both acidosis and alkalosis are severe conditions that require immediate medical attention.
Primary Causes of Systemic pH Disruption
Systemic pH disruption is secondary to a health condition that impairs the function of the lungs or kidneys, or alters metabolic processes. Respiratory imbalances are tied to the lungs’ ability to manage carbon dioxide levels. Respiratory acidosis is caused by hypoventilation, or inadequate breathing, which leads to CO2 retention. This is seen in conditions like Chronic Obstructive Pulmonary Disease (COPD), severe pneumonia, or a drug overdose that depresses the respiratory drive.
Respiratory alkalosis, conversely, is caused by hyperventilation, or breathing too rapidly, which results in excessive CO2 loss. This can be triggered by anxiety, fever, high altitude exposure, or certain neurological disorders that stimulate the respiratory center in the brain. The low CO2 level in the blood causes the pH to rise quickly.
Metabolic acidosis is often the result of either the overproduction of acid or the excessive loss of bicarbonate. A prime example is Diabetic Ketoacidosis (DKA), where the body, lacking sufficient insulin, breaks down fat for energy, producing large quantities of acidic ketone bodies. Lactic acidosis, another common cause, occurs when tissues suffer from a lack of oxygen, such as during shock or severe sepsis, forcing cells to produce lactic acid.
Metabolic alkalosis is most commonly caused by the loss of hydrogen ions, or acid, from the body. Prolonged and severe vomiting is a frequent trigger because it leads to the loss of stomach acid. This condition can also be caused by the overuse of certain diuretics, which increase the excretion of potassium and hydrogen ions in the urine, or by the excessive intake of alkaline substances like antacids.
Diagnosis and Treatment of Imbalance
Diagnosing a systemic pH imbalance begins with an Arterial Blood Gas (ABG) analysis. This test requires a small blood sample, typically drawn from an artery in the wrist, and provides immediate, detailed measurements. The ABG report includes the blood’s precise pH value, the partial pressure of carbon dioxide (PaCO2), and the level of bicarbonate (HCO3-).
These three values allow a physician to determine whether the patient is in acidosis or alkalosis and to classify the imbalance as respiratory or metabolic. Treatment for any pH imbalance is never focused on simply correcting the pH number itself; rather, it is always directed at resolving the underlying cause. For example, metabolic acidosis due to DKA requires insulin and intravenous fluids to manage blood sugar and flush out ketones.
If the issue is respiratory acidosis from a breathing disorder, treatment may involve bronchodilator medications or mechanical ventilation to improve CO2 expulsion. Medical intervention centers on restoring normal function to the lungs or kidneys, or controlling the metabolic process that initiated the disruption. This allows the body’s homeostatic mechanisms to re-establish the correct acid-base balance.