ABG Interpretation, part 2: Buffers in the Body
by Cathy Parkes June 03, 2021 Updated: July 29, 2021 5 min read
In the body, we have several buffers that help regulate the acid-base balance. Acid-base balance is measured by pH, and it's important for the body to keep the pH level within the normal range of 7.35 to 7.45. The body constantly works to achieve this homeostasis. Keeping pH levels within a normal range allows the body to function optimally. Blood that is too acidic or too basic can be dangerous, which is why pH is an important measurement in an Arterial Blood Gas test.
First line of defense: Chemical buffers
The first line of defense for regulation of the acid-base balance in the body are chemical buffers. These chemical buffers are present in our bodily fluids and act immediately to bind or release hydrogen ions and help promote acid-base balance in the body.
There are several chemical buffers you should be familiar with when it comes to ABGs. These include the carbonic acid-bicarbonate buffer system, the phosphate buffer system, and protein buffers, which include albumin, globulins, and hemoglobin.
For some chemistry background, a buffer is a solution, usually containing an acid and a base, that can resist pH change. These buffers are quite helpful when the body is seeking pH homeostasis!
Carbonic-acid-bicarbonate buffer system
The carbonic-acid-bicarbonate buffer system is a buffer solution made of carbonic acid (H₂CO₃, a weak acid), and bicarbonate (HCO₃). This buffer system plays a bigger role in regulating the pH of the blood than the following two.
Phosphate buffer system
The phosphate buffer system is another type of chemical buffer system in the body that works to regulate the pH of the blood. The phosphate buffer system consists of acidic phosphate ions and alkaline phosphate ions that work to neutralize pH.
Protein buffers: albumin, globulins, and hemoglobin
The protein buffers in our body are albumin, globulins, and hemoglobin. Proteins work well as buffers because they have both positive and negative charges on their surface, and can bind with acids to neutralize them.
Second line of defense: Respiratory system
If the chemical buffers are not able to regulate the acid-base levels in the arterial blood, then the respiratory system will kick in. The respiratory system is the second line of defense, and is able to control the amount of carbon dioxide in the arterial blood by regulating breathing.
High CO₂ level response
In response to high CO₂ levels in the arterial blood, the respiratory system will increase the depth and rate of breathing, leading to hyperventilation. In this case, hyperventilation is the body's attempt to reduce excess CO₂ and thus reduce excess hydrogen ions.
Low CO₂ level response
In response to low CO₂ levels in the arterial blood, the body will decrease rate and depth of breathing, leading to hypoventilation. In this case, hypoventilation is the body's attempt to retain more CO₂ and therefore, more hydrogen ions.
Third line of defense: Renal system
If the respiratory system is not able to regulate the acid-base levels in the arterial blood, then the renal system will kick in. The renal system is the third line of defense; slower to respond, but longer-acting.
If the renal system senses that the blood pH is too low/acidic (acidosis is present), the kidneys will increase reabsorption of bicarbonate, to retain more of it, and excrete more hydrogen ions.
If the renal system senses that the blood pH is too high/alkaline (alkalosis is present), it will increase excretion of bicarbonate (reduce bicarbonate) and increase reabsorption of hydrogen ions (retain more hydrogen ions).
The chemical buffers, respiratory system, and renal system are the body's backup methods for maintaining a healthy acid-base balance. If the body's backup systems fail, there are treatments for acid-base balances, which we'll cover in an article later in this series!
In this video, I want to briefly talk about the different buffers in the body that help to regulate acid-base balance. The first line of defense are chemical buffers in the body. The second line of defense is the respiratory system, and the third line of defense is the renal system.
So let's first talk about the first line of defense, which are chemical buffers.
So these chemical buffers are present in our bodily fluids and act immediately to bind or release hydrogen ions and help to promote an acid-base balance in the body.
So there are several different chemical buffers that I would be familiar with. One is the carbonic-acid-bicarbonate buffer system.
Then we also have the phosphate buffer system.
And then lastly, we have protein buffers, including albumin, globulins, and hemoglobin.
So if our chemical buffers don't get the job done, then it falls to the respiratory system to try to maintain an acid-base balance. So the respiratory system, it's the second line of defense, and it controls the amount of carbon dioxide in the arterial blood.
So in response to high CO2 levels, or high amount of carbon dioxide, in the arterial blood, the respiratory system will increase the depth and the rate of breathing. So basically you'll have hyperventilation to try to get rid of that excess CO2 and therefore, get rid of those excess hydrogen ions.
If the respiratory system senses that there are low CO2 levels in the arterial blood, then it will decrease the rate and depth of breathing, so meaning hypoventilation, to help your body retain more CO2 and therefore, more hydrogen ions.
Then if the respiratory system doesn't get the job done, then it falls onto the renal system which is the third line of defense. The renal system is slower to respond, but the response of the renal system is more powerful and more long-acting.
So the renal system, if it senses that the blood pH is too low, meaning there's acidosis present, the kidneys will increase reabsorption of bicarbonate. So we're going to keep more bicarbonate, and it will also excrete more hydrogen ions.
So we're getting rid of those hydrogen ions, and we're keeping more bicarbonate when the kidneys sense acidosis is present.
And then on the opposite, if the kidneys sense that the pH is too high, meaning we have alkalosis, it will increase excretion of that bicarbonate and increase reabsorption of those hydrogen ions.
So with those three systems in place, we hopefully will get to a place where we have acid-base balance. However, if the body doesn't get the job done with those three lines of defense, there are several things we do in terms of treatment of acid-base imbalances, and we'll definitely be going over those in a later video here.
So in my next video, we will start getting into interpretation of those ABG results, so thanks so much for watching!
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