Contraction alkalosis
Encyclopedia
Contraction alkalosis refers to the increase in blood pH that occurs as a result of fluid losses (volume contraction
). The change in pH is especially pronounced with acidic fluid losses caused by problems like vomiting
.
Increases in angiotensin II cause increased Na+-H+ exchange in the proximal tubule and increased HCO3- (bicarbonate) reabsorption in the proximal tubule
due to increased luminal H+. Increased aldosterone secretion stimulates the H-ATPase of alpha-intercalated cells of the collecting duct, which causes 1) increased distal tubule H+ secretion, worsening the metabolic alkalosis, and 2) increased generation of "new" bicarbonate within these same cells, which will be reabsorbed.
Additionally, increased aldosterone secretion causes increased distal tubule K+ secretion, in turn causing the hypokalemia
seen with contraction alkalosis.
Alkalosis also induces H+-efflux from cells through the K+-H+ exchanger, leading to hypokalemia.
infusion to correct ECF volume contraction and administration of K+ to replace urinary losses.
Volume contraction
Volume contraction is a decrease in body fluid volume, also including any concomitant loss of osmolytes. The loss of the water component of body fluid is specifically termed dehydration.-By body fluid compartment:...
). The change in pH is especially pronounced with acidic fluid losses caused by problems like vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
.
Pathophysiology
Extracellular fluid (ECF) volume contraction is associated with decreased blood volume and decreased renal perfusion pressure. Three compensation mechanisms engage as a result:- reninReninRenin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
secretion is increased, - production of angiotensin II is increased, and
- secretion of aldosteroneAldosteroneAldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
is increased.
Increases in angiotensin II cause increased Na+-H+ exchange in the proximal tubule and increased HCO3- (bicarbonate) reabsorption in the proximal tubule
Proximal tubule
The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.-Structure and appearance:...
due to increased luminal H+. Increased aldosterone secretion stimulates the H-ATPase of alpha-intercalated cells of the collecting duct, which causes 1) increased distal tubule H+ secretion, worsening the metabolic alkalosis, and 2) increased generation of "new" bicarbonate within these same cells, which will be reabsorbed.
Additionally, increased aldosterone secretion causes increased distal tubule K+ secretion, in turn causing the hypokalemia
Hypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
seen with contraction alkalosis.
Alkalosis also induces H+-efflux from cells through the K+-H+ exchanger, leading to hypokalemia.
Treatment
Treatment consists of NaClSodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
infusion to correct ECF volume contraction and administration of K+ to replace urinary losses.