Classification and main causes
There are three main forms of the pathology depending on the specific pathway through which the body loses essential ions:
- Gastric. Occurs with the loss of hydrochloric acid (HCl) along with gastric juice. The main cause is profuse and repeated vomiting. This condition is characteristic of toxicosis of pregnant women, pyloric stenosis, pylorospasm, as well as high intestinal obstruction.
- Intestinal (enteral). Associated with increased excretion of potassium ions (K^+) along with alkaline intestinal contents. It develops with the abuse of laxatives or overly frequent enemas.
- Renal. Caused by enhanced excretion of chlorides, potassium, and protons (H^+) in the urine, as well as excessive reabsorption of bases. A typical cause is prolonged diuretic therapy.
Pathogenesis of intestinal alkalosis
A key role in the development of the intestinal form is played by potassium loss. The chain of pathological disorders is as follows:
- Massive excretion of K^+ with feces leads to the development of pronounced hypokalemia.
- The body tries to compensate for the deficiency: sodium ions (Na^+), which are alkaline, rush from the intercellular fluid into the cells.
- This transport process occurs strictly in exchange for the exit of intracellular potassium or protons (H^+).
- As a result, sodium accumulates in the cells, and the loss of protons causes alkalosis — with the pH shift occurring both inside the cells and in the blood plasma.
How the kidneys exacerbate the problem
Any significant fluid loss (repeated blood loss, vomiting, diarrhea, increased sweating) reduces the circulating blood volume. Hypovolemia develops, which triggers the renin-angiotensin-aldosterone system (RAAS).
RAAS activation leads to secondary hyperaldosteronism. The hormone aldosterone forces the renal tubules to actively return sodium to the blood, while sharply increasing the release of H^+ and K^+ into the urine. Thus, the initially arising intestinal or gastric alkalosis is later potentiated (amplified) by a secondary renal mechanism.
Mechanisms of renal alkalosis during diuretic therapy
Diuretics cause renal alkalosis through several pathways at once. The basic principle is that increased sodium excretion by the kidneys is combined with bicarbonate retention. This is implemented through four mechanisms:
- Inhibition of sodium and water reabsorption. The tubular reabsorption of Na^+ and water is blocked. The concentration of alkaline bicarbonate anions in the blood plasma relatively increases (concentration alkalosis is formed).
- Hypochloremic mechanism. Chlorine (Cl^-) is actively excreted along with sodium, forming hypochloremia and the corresponding hypochloremic alkalosis.
- Cellular shift. Due to diuretic-induced hypokalemia, protons move from the intercellular fluid into cells (in exchange for potassium to compensate for its deficiency in plasma). A decrease in H^+ concentration in the extracellular environment enhances alkalosis.
- "Poorly absorbable anions" factor. Sulfates, nitrates, or penicillin metabolites may enter the glomerular filtrate with food or medications. They are poorly reabsorbed in the proximal tubules. The accumulation of these anions in the primary urine requires enhanced excretion of cations to maintain electroneutrality, which is accompanied by H^+ secretion and aggravates the pH shift.
Briefly: answers to topical questions
By means of which specific physiological mechanisms (respiratory, renal) does the body compensate for metabolic alkalosis?
Compensation for metabolic alkalosis is carried out using urgent and long-term mechanisms aimed at eliminating or reducing the degree of disorders.
- Respiratory compensation — a decrease in alveolar ventilation volume (hypoventilation), which leads to carbon dioxide retention and the development of respiratory acidosis.
- Renal compensation — enhanced renal excretion of excess bicarbonates.
- Activation of cellular mechanisms — protein buffering, as well as enhanced glycolysis and tricarboxylic acid cycle processes.
- Ion exchange — an increase in the exchange of intracellular chlorine for extracellular bicarbonate.
- Extracellular buffering — recruitment of extracellular buffer systems with low capacity.
What clinical symptoms are observed in a patient with severe excretory alkalosis?
Clinical manifestations directly indicated in sources for electrolyte disorders associated with alkalosis:
- Tetanic convulsions.
- Bronchospasm.
- Laryngospasm with the risk of pulmonary failure and asphyxia.
- Muscle weakness in hypokalemia.
What ECG changes are characteristic of excretory alkalosis accompanied by hypokalemia?
If excretory alkalosis is accompanied by hypokalemia, the following ECG signs are indicated in hypokalemia sources:
- Low T-wave voltage.
- ST-segment depression.
- Extrasystole.
To remember the three types of excretory alkalosis, focus on the "floors" of losses: upper floor (stomach — losing acid with vomiting), lower floor (intestine — losing potassium with laxatives), and filter (kidneys — losing chlorine and protons due to diuretics).
Class and exam questions
Why does alkalosis develop during potassium loss?
In hypokalemia, the body tries to replenish plasma potassium levels by releasing it from cells. In exchange, hydrogen ions (H+) move inside the cells. A decrease in proton concentration in the extracellular fluid shifts the pH toward the alkaline side.
What is hypochloremic alkalosis?
This is a variant of the disorder in which the kidneys excessively excrete chlorine ions (Cl-) along with sodium. Most often, this condition develops against the background of prolonged use of diuretic drugs.
How does the body compensate for excretory alkalosis?
Mechanisms completely analogous to those operating in classical metabolic alkalosis are activated. The main goal of compensation is to maximally reduce the concentration of bicarbonate (HCO3-) in the blood plasma.
What else to study on this topic
- Mechanisms of metabolic alkalosis compensation
- The role of the renin-angiotensin-aldosterone system (RAAS) in pH regulation
- Intracellular alkalosis: impact on metabolism
- Pharmacodynamics of diuretics and their effect on electrolyte balance
- Pathophysiology of hypovolemia and mechanisms of circulatory centralization
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Excretory alkalosis" and another 4,913 pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics in "Chapter 13. Acid-Base Disorders"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.