Role of lungs and kidneys
The lungs are the most agile link: changes in alveolar ventilation allow ABB shifts to be corrected within just a couple of minutes.
The kidneys 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, in which ammonia binds $H^+$, forming ammonium ions ($NH_4^+$).
- Phosphate secretion: excretion of $NaH_2PO_4$ with urine, which allows bicarbonate to be returned to the blood to maintain buffer capacity.
Involvement of the liver and GI tract
The liver participates in regulation via metabolic pathways. For example, gluconeogenesis from lactate and pyruvate helps reduce the concentration of organic acids during acidosis. Hepatocytes also synthesize proteins that function as buffer systems.
The digestive 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
ABB disorders are divided into acidosis (excess acids, pH < 7.39) and alkalosis (excess bases). By origin, they are classified as:
- Respiratory (associated with pulmonary ventilation).
- Non-respiratory (metabolic, excretory, or mixed).
Depending on severity, the process can be compensated, subcompensated, or uncompensated.
Briefly: answers to topical questions
Which blood buffer systems react first to ABB shifts?
The physicochemical buffer systems of the blood react instantly and first to acid-base balance shifts. The 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, hydrochloric acid secretion in the stomach increases, while pancreatic bicarbonate secretion decreases. The digestive organs participate in damping acid-base balance shifts as follows:
- Stomach — during acidification, hydrochloric acid (HCl) secretion increases, ensuring the removal of hydrogen ions from the blood.
- Pancreas — during acidosis, bicarbonate secretion decreases, whereas during alkalosis, it increases instead.
What laboratory blood parameters are used to assess ABB?
To assess acid-base balance and its shifts in clinical practice, blood parameters are used along with their normal ranges:
- pH;
- pCO₂;
- SB (Standard Bicarbonate) — blood plasma standard bicarbonate;
- BB (Buffer Base) — capillary blood buffer bases;
- BE (Base Excess) — base excess of capillary blood.
Blood parameters also indicated in sources include:
- Blood CT: 0.5–2.5 mg%;
- Blood lactic acid: 6–16 mg%.
"The lungs are speed, the kidneys are capacity, the liver and GI tract are metabolic tuning."
Class and exam questions
Why do the lungs react to ABB shifts faster than the kidneys?
The lungs utilize a mechanism of alveolar ventilation changes, which is reflexively triggered within 1–2 minutes. Renal mechanisms require time for enzymatic processes and ion transport in the tubules.
What is the essence of ammoniagenesis?
This is the process of ammonia formation in the tubular epithelium, which binds hydrogen ions. As a result, ammonium is formed and excreted in the urine, while sodium bicarbonate is returned to the blood.
How does the stomach help during alkalosis?
During alkalinization of the body, hydrochloric acid secretion in the stomach is inhibited, which preserves more hydrogen ions in the body to neutralize the excess bases.
What else to study on this topic
- The mechanism of $K^+$, $Na^+$ exchange in the distal tubules under the influence of aldosterone.
- The role of the protein buffer system in blood plasma.
- Detailed analysis of non-volatile acid excretion by the liver.
- The relationship between gluconeogenesis and combating acidosis.
- Mechanisms of absorption of buffer system components in the intestine.
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