CO2made in the beige cells gets converted to H2CO3 and H+
Need carbonic anhydrase to make this fast
Some CO2goes and binds to hemoglobin
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Some CO2in RBC's just gets out
Some bicarb goes in the opposite reaction to make CO2so it can get released
CO2Exodus
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CO2Generation and Transport
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Dissolved CO2 yields H+ because of the carbonic acid-bicarbonate buffer reaction
Anything that interferes with respiration will increase dissolved CO2 because without being able to breath properly you cannot exhale the CO2 produced
Damage to the lungs (e.g., emphysema) or airways (e.g., obstruction) or breathing (damage to the muscles of respiration) □
Damage (trauma) or incapacitation (e.g., opiate poisoning) of respiratory centers in medulla oblongata □
Just holding your breath or running will do it too! □
Causes of respiratory acidosis….
Acute respiratory acidosis increases epinephrine and norepinephrine release. □
This is so you become aggressive to try and breathe □
Note:
Respiratory Causes ○
Anything except for CO2 causing an increase in H+ is called nonrespiratory or metabolic acidosis
Lactic acid produced during glycolysis under anaerobic conditions
Anaerobic metabolism □
Normally the kidney secretes large amounts of acid and when it is not functioning properly pH will fall.
Kidney dysfunction □
Uncontrolled diabetes and other forms of starvation lead to large increases in fatty acids
The breath smells fruity because of the ketones ◊
When there are large amounts of unmetabolized fatty acids around this brings down the pH, ketones also arise so this state is called ketoacidosis.
Incomplete breakdown of fatty acids □
Causes of Acidosis
Consumption of ethanol in large quantities (it is converted from ethanol to acetaldehyde and then acetic acid) or small amounts of methanol or other toxic alcohols
Normal metabolism produces lots of sulfuric and other acids every day
These sorts of acids are called nonvolatile to distinguish them from carbon dioxide.
Acidic fruits which have citric and other acid (this is a very minor contribution)
The loss of bicarbonate rich intestinal fluid leads to acidosis □
Bowel normally dries feces and draws out water and bicarb … which is a base □ Diarrhea Nonrespiratory Causes ○ Acidosis •
Hyperventilation drives down the alveolar CO2 and since your blood stream CO2 is in equilibrium with the alveolar levels then your blood loses CO2
You can easily develop low carbon dioxide levels in the blood because of hyperventilation (i.e., excessive amounts of deep br eathing) □
With low CO2 in the blood and the accompanying elevated pH one loses the drive to breath □
This is like a reboot … this stops the breathing so there is a build up of CO2
People commonly “pass out” when they hyperventilate and quit breathing for a few moments. This decrease in ventilation reesta blishes high enough CO2 levels to stimulate breathing.
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Respiratory alkalosis is caused by low amounts of CO2 in the blood stream
Respiratory Causes ○
Loss of H+ from the extremely acidic contents of the stomach will lead to an increase in pH □
Vomiting
Bicarbonate is a base so consumption of this basic material consumes some of the blood H+ and pH goes up □
Ingestion of bicarbonate
Normally the feces are expelled with a small amount of water and bicarbonate. If the fecal material stays in the large bowel long enough it becomes very dehydrated and much of the bicarbonate, which is normally lost, is reabsorbed.
Absorption of extra bicarbonate from the feces. □ Constipation Nonrespiratory Causes ○ Alkalosis •
We compensate for the changes by one of two ways ○
Greater ventilation of the alveoli decreases the amount of CO2 in the alveoli. The decrease in alveolar CO2 causes a greater concentration gradient between the CO2 in the blood and the alveolar space. With a large concentration gradient the CO2 rapidly leaves the blood. Wi th less CO2 the □
If there is too much acid or lots of CO2 we breath more
Respiratory Compensation ○
What does one do about changes in pH? •
between the CO2 in the blood and the alveolar space. With a large concentration gradient the CO2 rapidly leaves the blood. Wi th less CO2 the bicarbonate buffer system shifts to the left and consumes H+.
Less ventilation causes an increase in alveolar CO2 which leads to a smaller concentration gradient between the CO2 in the bl ood and the alveolar space. With a smaller concentration gradient the CO2 builds up in the blood. More CO2 leads to a shift to the right in the bi carbonate buffer system which yields an increase in H+.
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If there is too little acidity or low CO2 we breath less
CO2levels are more important than O2levels in terms of the breathing rate
□ Note:
If there is too much acid (low pH), we pee out acids (H+) □
If there is too much base (high pH), we pee out base (HCO3-) □
This is fundamentally a very, very simple system
The process of renal compensation for acidosis is better than respiratory compensation because HCO3 - is preserved by the kidneys □
Therefore you are able to preserve HCO3- levels in the bod ◊
For long term compensation of acidosis the bicarbonate can be preserved by using the kidneys
Respiratory compensation “costs” one HCO3- for each H+ (i.e., one bicarbonate has to combine with a hydrogen ion which results in H2O and CO2. The CO2 is expired at the lungs thus one bicarbonate ion is lost) but renal compensation does not cost a bicarbonate.
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The kidneys are also the only way of dealing with nonvolatile acids i.e., acids which cannot leave in the respiratory gas. □
It takes hours for this system to kick in and days for it to become optimized □
Characteristics
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High H+ levels will lead to increases in CO2 □
The CO2 can then move passively into the tubular cell. □
The CO2 combines with water to form H2CO3 which dissociates to HCO3- and H+ □
The H+ is put into the filtrate using the Na/H+ antiporter. □
The HCO3- is passively reabsorbed to the capillary blood □
The Na+ that came in on the antiporter is pumped out using a Na+ pump. □
This rapid conversion of carbonic acid to the bicarbonate ion and H+ allows for the regulation of the ions.
The CO2 could move in any direction but only the cell can deal can create the bicarbonate ions and shunt them back to the blood.
The “secret” here is carbonic anhydrase (CA) which converts the CO2 to H2CO3 □
Notice that the H+ is excreted and the HCO3- is reabsorbed which is not like the respiratory compensation for excess H+. □
Na+/H+ Antiporter in the Proximal C.T.
Renal Compensation ○
If pH is >7.45 you have an alkalosis ○
If pH is <7.35 you have an acidosis ○
The next value to check is the amount of CO2 in the blood to discover if it is higher or lower than normal ○
The final thing is to combine the two measures and think about what you are seeing! ○
First you have to decide whether the situation you are seeing is acidosis or alkalosis
Next you have to figure our whether it is respiratory or nonrespiratory.
Steps ○
If the CO2 levels agree with the pH it will be called “respiratory acidosis”
If the CO2 levels do not “agree with” (or explain) the pH then it will be called “nonrespiratory acidosis”
THIS WILL BE ON THE EXAM FOR SURE
Inference ○
You can also check bicarbonate levels when investigating the cause of an acid-base imbalance.
Example 1. In severe diarrhea there is a loss of bicarbonate and the pH is low. The low bicarbonate is the problem (not CO2 I t is a case of metabolic acidosis because the low pH is not due to too much CO2 . A cure for this problem, besides stopping the diarrhea, is to provi de intravenous bicarbonate.
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Example 2. In the case of vomiting there is a loss of H+ and there is lot of excess bicarbonate left around in the plasma. T his is a metabolic alkalosis because the problem is not due to a low CO2. The cure for the problem is to stop the loss of the unbuffered H+.
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Bicarbonate is a base so the pH should vary directly with the bicarbonate levels if the bicarbonate is causing the problems (i.e., low pH with low bicarbonate levels and high pH with high bicarbonate levels)
Bicarbonate Levels ○
An Introduction to Figuring out the Causes of Acidosis and Alkalosis •
A: 1. The pH is higher than normal, so this is a case of alkalosis.
2. In this case venous CO2 is low which leads to small amounts H+ and a high pH. The CO2 and the pH agree which is to say that the low CO2 is causing the problem. This must be a respiratory alkalosis.
The person has likely hyperventilated since that is by far the commonest cause of this finding.
You don’t have to look at bicarbonate levels here because the cause is clear, however, bicarbonate would be low because there is little CO2 around to make bicarbonate.
Q: After spending several anxious hours waiting to begin the Anatomy and Physiology exam, a student collapses. In the emergency room the blood results show an elevated pH and a low CO2. What is the problem?
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Q: Later that evening after the highly stressful but stimulating and rewarding A&P exam the same student is found semiconscious outside of residence clutching a Problems
A: 1. There is low pH, so this is a case of acidosis.
2. Low CO2 alone leads to small amounts of H+ and a high pH but there is a low pH here. The pH reading and the CO2 measure do not agree therefore the CO2 cannot be causing the problem so it must be a nonrespiratory (metabolic) acidosis.
The low CO2 is a result of compensation by the respiratory system. The low CO2likely means this person was or is breathing deeply.
Notice as well that the low levels of bicarbonate are, in a sense, the cause of the problems. If there was more bicarbonate then the pH would be higher.
The large amounts of alcohol consumed by the patient were converted to acetic acid which leads to increase amounts of fixed acids. If this person had vomited then the pH would have gone back up but she held on with great resolve.
Q: Later that evening after the highly stressful but stimulating and rewarding A&P exam the same student is found semiconscious outside of residence clutching a half-consumed bottle of peach schnapps mumbling the score to “Mamma Mia.” Back in the ER the blood results come back showing a depressed pH and a low CO2 and low bicarbonate. What is the problem?
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The bicarbonate buffer system is an equilibrium reaction which is critical to understanding acid-base balance. ○
The ventilation of the lungs is critical to maintenance of blood pH so any problems can cause alterations respiratory alkalosis or acidosis ○
The kidneys can both generate new bicarbonate and excrete H+ as well as compensate for pH changes ○
We can compensate for lots of problems with pH so you can have high CO2 and low CO2 and still have normal pH. ○
But…. when given a problem about pH on a test or in real life use a systematic approach or suffer the consequences! ○
Summary •