Metabolic alkalosis & Acid-base disturbance - USMLE Forums
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Old 06-28-2011
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Arrow Metabolic alkalosis & Acid-base disturbance

Acid base disturbances can be confusing, so I thought I'd share some tips.
Couple rules of thumb:
1. If the disturbance in metabolic (i.e. problem with HCO3-), the compensatory response will be respiratory (i.e. CO2) and vice versa.
2. The compensatory response is always in the same direction as the original disturbance. For example, if there is a decrease in HCO3- leading to metabolic acidosis, there will be a decrease in CO2 to compensate.

Someone asked me the question how does a loss of H+ lead to increase in HCO3- and here's my response:
The gist of it is that bicarb buffers acid, so if you lose acid, there's going to be more unbuffered bicarb lying around. Let's use vomiting as an example.
1. The gastric parietal cells make H+ and HCO3- from CO2 and H2O.
2. H+ is secreted into the stomach to acidify it, and HCO3- goes into the blood.
3. The H+ from the stomach travels in the acidic chyme to the duodenum.
4. Low pH in the duodenum triggers HCO3+ release from the pancreas.
Therefore, the HCO3- added to blood by the parietal cell is later removed from blood in pancreatic secretion, so there is no net increase in bicarb in blood.
In vomiting, the H+ from the stomach doesn't reach the duodenum because it's lost in vomit. Therefore, there is no stimulus to cause the pancreas to secrete bicarb, and that HCO3- stays in the blood, leading to metabolic alkalosis.

Last edited by heights; 06-28-2011 at 11:25 PM. Reason: spelling
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Old 06-28-2011
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I always hated acid-base balance!!:
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Old 04-15-2014
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Default need help I am really stuck a confused

Quote:
Originally Posted by heights View Post
Acid base disturbances can be confusing, so I thought I'd share some tips.
Couple rules of thumb:
1. If the disturbance in metabolic (i.e. problem with HCO3-), the compensatory response will be respiratory (i.e. CO2) and vice versa.
2. The compensatory response is always in the same direction as the original disturbance. For example, if there is a decrease in HCO3- leading to metabolic acidosis, there will be a decrease in CO2 to compensate.

Someone asked me the question how does a loss of H+ lead to increase in HCO3- and here's my response:
The gist of it is that bicarb buffers acid, so if you lose acid, there's going to be more unbuffered bicarb lying around. Let's use vomiting as an example.
1. The gastric parietal cells make H+ and HCO3- from CO2 and H2O.
2. H+ is secreted into the stomach to acidify it, and HCO3- goes into the blood.
3. The H+ from the stomach travels in the acidic chyme to the duodenum.
4. Low pH in the duodenum triggers HCO3+ release from the pancreas.
Therefore, the HCO3- added to blood by the parietal cell is later removed from blood in pancreatic secretion, so there is no net increase in bicarb in blood.
In vomiting, the H+ from the stomach doesn't reach the duodenum because it's lost in vomit. Therefore, there is no stimulus to cause the pancreas to secrete bicarb, and that HCO3- stays in the blood, leading to metabolic alkalosis.


I wanted to know that in respiratory alkalosis due to hyperventilation pac02 falls and according to equation CO2 (g) + H20 (l) <=> H2CO3 (aq) <=> H+ (aq) + HCO3- (aq ) it shifts to right.in literature they say H+ and HCO3 combine to form carbonic acid and it dissociates into co2 and h2o.but they say protons are lost and ph rises causing alkalosis. My question is when H+ AND HCO3 both combine and so are lost then why ph rises.shoudnt ph stay unchanged.if my question is not clear I can elaborate.
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