Home › Pathophysiology › Physiological Mechanisms of Acid-Base Balance Regulation

Physiological Mechanisms of Acid-Base Balance Regulation

Q: Which blood buffer systems are the first to respond to acid-base shifts?

The physicochemical buffer systems of the blood react instantly to acid-base shifts. Total buffer capacity is distributed between plasma (43%) and erythrocytes (57%). This first line of defense includes: Bicarbonate buffer — present in both media (plasma and erythrocytes).Hemoglobin buffer — located exclusively in erythrocytes.Protein buffer — located predominantly in blood plasma.Phosphate buffer — plays a minor role directly in the blood.

Q: How exactly do the secretory functions of the stomach and pancreas change during acidosis?

During acidosis, gastric hydrochloric acid secretion increases, while pancreatic bicarbonate secretion decreases. The digestive organs buffer acid-base shifts as follows: Stomach — during acidification, hydrochloric acid ($HCl$) secretion increases, removing hydrogen ions from the blood.Pancreas — during acidosis, bicarbonate secretion decreases, whereas during alkalosis, it increases.

Q: What laboratory blood parameters are used to evaluate acid-base status?

To evaluate acid-base status and its shifts clinically, blood parameters are used along with their normal ranges: pH;pCO₂;SB (Standard Bicarbonate) — standard plasma bicarbonate;BB (Buffer Base) — buffer bases of capillary blood;BE (Base Excess) — base excess of capillary blood. Additional parameters mentioned in literature: Blood ketone bodies: 0.5–2.5 mg%;Blood lactic acid: 6–16 mg%.

Q: Why do the lungs react to acid-base shifts faster than the kidneys?

The lungs use the mechanism of alveolar ventilation changes, which is triggered reflexively within 1–2 minutes. Renal mechanisms require time for enzymatic processes and ion transport in the tubules.

Q: What is the essence of ammoniagenesis?

It is the production of ammonia in the tubular epithelium, which binds hydrogen ions. This results in the formation of ammonium, which is excreted in the urine, while sodium bicarbonate is returned to the blood.

Q: How does the stomach help during alkalosis?

During body alkalinization, hydrochloric acid secretion in the stomach is inhibited, which preserves more hydrogen ions in the body to neutralize the excess base.

Acid-Base Balance

For medical students2 min readUpdated 2026-10-10

The regulation of acid-base balance (ABB) encompasses the physiological processes that maintain blood pH homeostasis. The primary organs involved are the lungs, kidneys, liver, and gastrointestinal tract, which provide compensation during acidosis or alkalosis.

LungsRapid response (1–2 minutes) via changes in alveolar ventilation.

KidneysAcidogenesis, ammoniagenesis, and phosphate secretion to regenerate bicarbonate.

LiverMetabolic neutralization of acids and synthesis of buffer proteins.

GI TractRegulation via gastric HCl secretion and pancreatic bicarbonate secretion.

Role of the Lungs and Kidneys

The lungs are the most mobile component: changes in alveolar ventilation adjust acid-base shifts within a couple of minutes.

Kindeys act more slowly, but provide deep correction through three key processes:

Acidogenesis: energy-dependent secretion of hydrogen ions ($H^+$) in exchange for sodium.
Ammoniagenesis: oxidative deamination of amino acids, where ammonia binds $H^+$, forming ammonium ions ($NH_4^+$).
Phosphate secretion: excretion of $NaH_2PO_4$ in the urine, allowing bicarbonate to return to the blood to maintain buffer capacity.

Involvement of the Liver and GI Tract

The liver participates in regulation through metabolic pathways. For instance, gluconeogenesis from lactate and pyruvate helps reduce organic acid concentrations during acidosis. Hepatocytes also synthesize proteins that function as buffer systems.

Gastrointestinal organs act as a "chemical regulator":

Stomach: inhibits hydrochloric acid secretion during alkalosis, and enhances it during acidosis.
Pancreas: regulates bicarbonate levels depending on the current blood pH.

Classification of Disorders

Acid-base disorders are divided into acidosis (excess acid, pH < 7.39) and alkalosis (excess base). By origin, they are classified as:

Respiratory (associated with pulmonary ventilation).
Non-respiratory (metabolic, excretory, or mixed).

Depending on the severity, the process can be compensated, partially compensated, or uncompensated.

Mnemonic

"The lungs are speed, the kidneys are capacity, the liver and GI tract are metabolic tuning."

Frequently asked questions

Which blood buffer systems are the first to respond to acid-base shifts?

The physicochemical buffer systems of the blood react instantly to acid-base shifts. Total buffer capacity is distributed between plasma (43%) and erythrocytes (57%). This first line of defense includes:

Bicarbonate buffer — present in both media (plasma and erythrocytes).
Hemoglobin buffer — located exclusively in erythrocytes.
Protein buffer — located predominantly in blood plasma.
Phosphate buffer — plays a minor role directly in the blood.

How exactly do the secretory functions of the stomach and pancreas change during acidosis?

During acidosis, gastric hydrochloric acid secretion increases, while pancreatic bicarbonate secretion decreases. The digestive organs buffer acid-base shifts as follows:

Stomach — during acidification, hydrochloric acid ($HCl$) secretion increases, removing hydrogen ions from the blood.
Pancreas — during acidosis, bicarbonate secretion decreases, whereas during alkalosis, it increases.

What laboratory blood parameters are used to evaluate acid-base status?

To evaluate acid-base status and its shifts clinically, blood parameters are used along with their normal ranges:

pH;
pCO₂;
SB (Standard Bicarbonate) — standard plasma bicarbonate;
BB (Buffer Base) — buffer bases of capillary blood;
BE (Base Excess) — base excess of capillary blood.

Additional parameters mentioned in literature:

Blood ketone bodies: 0.5–2.5 mg%;
Blood lactic acid: 6–16 mg%.

Why do the lungs react to acid-base shifts faster than the kidneys?