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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. ==Pathophysiology== There are several possible explanations for the process of alkalosis observed after volume contraction. One popular theory is that alkalosis is simply the loss of solvent volume without a proportional loss in bicarbonate concentration or increase in carbon dioxide concentration. This explanation may be especially appropriate for the very short term after volume loss. Another suggests that the alkalosis is due to renal compensatory mechanisms used to correct volume loss. Extracellular fluid (ECF) volume contraction is associated with decreased blood volume and decreased renal perfusion pressure. Three compensation mechanisms engage as a result: # renin secretion is increased, # production of angiotensin II is increased, and # secretion of aldosterone is increased. 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. Aldosterone also induces H+-efflux from cells through the K+-H+ exchanger, which could be a possible mechanism for the development of alkalosis. Finally, it has been suggested that the term "contraction alkalosis" is actually a misnomer, and that the alkalosis observed during volume contraction is actually attributable entirely to chloride depletion, which leads to a failure of pendrin, a chloride/bicarbonate exchanger in the collecting duct. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Contraction alkalosis」の詳細全文を読む スポンサード リンク
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