Balancing Act: Acid-Base in Human Health

The concept of acid-base balance is fundamental to how the human body works. Blood pH in humans is tightly regulated between 7.35 and 7.45. This narrow range is slightly alkaline, and even a small deviation can have serious effects. If blood pH drops below 7.35, the condition is called acidosis. If it rises above 7.45, it’s called alkalosis. Both conditions can be life-threatening because they interfere with basic cellular functions. The pH scale, which measures acidity and alkalinity, was introduced in 1909 by Søren Peder Lauritz Sørensen, a Danish chemist. Sørensen’s scale made it possible to quantify how acidic or basic a solution is, which led to greater scientific precision in both chemistry and biology.

The pH scale runs from 0 to 14. A solution with a pH of 7 is neutral. Solutions below 7 are acidic, and those above 7 are alkaline, or basic. Human blood sits just above neutral. The body relies on multiple buffer systems to maintain this balance. The most important is the bicarbonate buffer system. It’s based on the equilibrium between carbonic acid (H2CO3) and bicarbonate ion (HCO3-). This buffer system allows the blood to absorb and neutralize small amounts of acid or base, helping keep the pH in the safe zone. There are also the phosphate buffer system and protein buffers, which provide additional regulation.

In the 1920s, Lawrence J. Henderson and Karl Albert Hasselbalch described the mathematical relationship between pH, bicarbonate, and carbonic acid in the blood. This relationship is known as the Henderson-Hasselbalch equation. Their work made it possible to calculate blood pH changes based on the concentrations of these substances, which is crucial for diagnosing and treating acid-base disorders.

Acid-base disturbances can be respiratory or metabolic in origin. Hyperventilation, which is rapid or deep breathing, can cause respiratory alkalosis. That happens because breathing out too much carbon dioxide decreases the level of carbonic acid in the blood, pushing the pH higher. The opposite is hypoventilation, when breathing is too slow or shallow. In that case, carbon dioxide builds up, increasing acidity and causing respiratory acidosis.

The kidneys play a vital role in long-term pH regulation. They excrete hydrogen ions and reabsorb bicarbonate, which helps neutralize acids in the blood. This process of renal compensation means that even if a respiratory imbalance occurs, the kidneys can gradually restore balance by adjusting urine composition. This mechanism is slower than the respiratory response but essential for chronic disturbances.

By the 1950s, advances in medical technology allowed for a better understanding of acid-base disorders. In the 1970s, arterial blood gas (ABG) analysis became a standard diagnostic tool. ABG measures not only the pH of blood but also the partial pressures of oxygen and carbon dioxide, as well as bicarbonate levels. This data is used to assess a patient’s acid-base status quickly and accurately, which can be critical in emergency medicine.

The body’s buffer systems are constantly at work. Protein buffers, for example, use the amino acid side chains to bind or release hydrogen ions. Hemoglobin, the protein that carries oxygen in red blood cells, also helps buffer acids produced during metabolism. The phosphate buffer system works primarily inside cells and in the kidneys. It involves phosphate ions absorbing excess hydrogen ions, which helps keep cellular and urinary pH stable.

Diet influences acid-base balance, but only to a limited extent. Consuming foods that are more acidic or alkaline can change the pH of urine, but these dietary habits do not significantly alter blood pH because the body’s regulatory systems are so effective. This is why so-called “alkaline diets” have minimal effect on overall acid-base status, even though they can change how acidic or alkaline urine becomes.

Cultural beliefs about acid and base have shaped dietary practices in many societies. Some traditional health systems suggest that foods with certain acidic or alkaline properties can influence health outcomes. These beliefs have led to popular dietary trends that emphasize the consumption of alkaline foods for wellness. However, scientific evidence indicates that the body’s buffering capacity ensures that blood pH remains constant regardless of moderate dietary changes.

Supplementation with alkaline minerals, such as potassium citrate or sodium bicarbonate, is sometimes used in clinical settings to treat metabolic acidosis. These supplements provide additional alkaline substances that the body can use to neutralize excess acid. In chronic kidney disease, where the kidneys are less able to excrete acid, such supplementation can help maintain acid-base balance. However, supplementation without medical supervision can disrupt normal regulation and cause dangerous shifts in blood chemistry.

Certain medical conditions disrupt acid-base balance in distinct ways. For example, uncontrolled diabetes can lead to diabetic ketoacidosis. In this condition, the body produces large amounts of acidic ketone bodies, which lower blood pH. In contrast, prolonged vomiting can result in metabolic alkalosis by causing the loss of hydrochloric acid from the stomach.

Dr. Lawrence J. Henderson, who contributed to the foundational understanding of acid-base physiology, described acid-base balance as fundamental to homeostasis. Homeostasis refers to the body’s ability to maintain internal stability, which is essential for proper function of enzymes, nerve impulses, and muscle contractions. Dr. Karl Albert Hasselbalch emphasized that understanding acid-base balance is critical for diagnosing and treating a wide range of medical conditions, from kidney disease to respiratory infections.

Acid-base disturbances affect mental health in several ways. Extreme acidosis can cause confusion, lethargy, and even coma, as nerve and brain cell function becomes impaired. Alkalosis can lead to tingling sensations, muscle twitching, and in severe cases, seizures. This is because nerve cells rely on a specific pH range to regulate electrical activity and neurotransmitter function.

Globally, some cultures have developed rituals or health practices based on the perceived acid or alkaline nature of foods and medicines. These practices are often tied to beliefs about balance and harmony in the body. While cultural approaches can influence dietary choices and health behaviors, the physiological regulation of blood pH is largely independent of these traditions due to the efficiency of the body’s buffer systems.

The use of arterial blood gas analysis introduced in the 1970s provided doctors with a rapid and reliable way to detect life-threatening acid-base disorders. By measuring pH, carbon dioxide, oxygen, and bicarbonate directly in the blood, clinicians could diagnose respiratory or metabolic imbalances on the spot. This led to faster treatment of critical conditions in both emergency and intensive care settings.

Protein buffers play a unique role because they’re present in high concentrations inside cells. The imidazole groups in histidine residues of proteins can accept or donate hydrogen ions, making them effective at stabilizing pH in both intracellular and extracellular environments.

Urinary pH can range from about 4.5 to 8.0, reflecting the body’s effort to excrete acids or bases as needed. This wide variability helps the kidneys protect blood pH from fluctuations caused by diet, metabolism, or disease.

In 1909, when Sørensen introduced the pH scale, he used it to measure hydrogen ion concentration in beer during his work at the Carlsberg Laboratory. This practical application of chemistry sparked decades of research, leading to new discoveries about how life maintains its delicate balance between acid and base.