MudPhud20XX

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Nov 26, 2013
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So FA mentions "contraction alkalosis" in cystic fibrosis and in angiotensin II. Can anyone explain this? What do you mean by "contraction?" Many thanks!
 

Dr.serotonin

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Jun 30, 2015
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So FA mentions "contraction alkalosis" in cystic fibrosis and in angiotensin II. Can anyone explain this? What do you mean by "contraction?" Many thanks!
whenever the vascular fluid level decreases it stimulates Renin-Angiotensin-Aldosterone system (RAAS). angiotensin 2 has two major actions;
1] it enhances the Na/H antiport activity in PCT, increasing the Na reabsorption in exchange of proton ions.
2] it stimulates aldosterone release from zona glomerulosa which ultimately increase Na reabsorption in Late DCT and early collecting ducts and release Proton into the lumen.
both above actions results in proton loss in urine. and on the other hand creating an Alkalotic condition inside the body. this alkalosis that results from contraction of vascular space [decreased fluid in vascular compartment] is called contraction Alkalosis.
 
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Jun 30, 2015
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Zurich, Switzerland
Hi metabolic alkalosis can be grouped in 4-5 broad groups
  • GI H+ loss
  • Renal H+ loss
  • H+ shift inside cell
  • Administration of "HCO3-"
  • and contraction alkalosis
If you lose a big volume of bicarbonate-free fluid and you have a relatively constant amount of extracellular bicarbonate, contraction alkalosis occurs. In CF you loose a solution of high-sodium chloride (and not so much HCO3-), that's why contraction alkalosis occurs.

1] it enhances the Na/H antiport activity in PCT, increasing the Na reabsorption in exchange of proton ions. → H+ ↑ secretion in proximal tubule (due to AII) → leads to → HCO3-↑ reabsorption in proximal tubule (due to H+ ↑ secretion)
2] it stimulates aldosterone release from zona glomerulosa which ultimately increase Na reabsorption in Late DCT and early collecting ducts and release Proton into the lumen.
both above actions results in proton loss in urine. and on the other hand creating an Alkalotic condition inside the body. this alkalosis that results from contraction of vascular space [decreased fluid in vascular compartment] is called contraction Alkalosis.

As a side note:
Use of the term "contraction alkalosis" to characterize the metabolic alkalosis associated with vomiting, nasogastric suction, and diuretic use is confusing. In such settings, the generation of bicarbonate by the stomach or kidneys plays a crucial role in the development of these metabolic alkalosis.