Many organs talk to each other to perform specific roles to achieve a balance called homeostasis, which is crucial for survival. Acid-base homeostasis is a type of homeostasis that’s important for proper functioning of many biological processes. Sometimes when organs aren’t working the way they should, they can interrupt normal acid-base homeostasis. But first, let’s look at what “acid” and “base” mean.
The amount of acid or base in a solution is measured using a pH scale ranging from 0 to 14, with 7 being neutral. An acid, with a pH value of less than 7, is a substance that releases a positively charged hydrogen ion. Lemon juice is an example of an acid. A base is a substance that releases a negatively charged hydroxide ion and has a pH value above 7. Soap and bleach are examples of basic substances.
Now think back to childhood when you were on the playground. Imagine the seesaw as your acid-base homeostasis. Under normal conditions, the seesaw is perfectly balanced with a pH between 7.35 and 7.45. However, another kid (a hydrogen ion) on the playground just hopped on the left side of the seesaw, skewing the balance toward more acidic. This is called acidosis and can happen when a person has kidney or respiratory problems.
The reason kidney and lung disorders can disrupt acid-base homeostasis is because these are the two organs involved in maintaining that balance in the first place. On one side of the seesaw are the kidneys, which are built-in filters responsible for removing any excess acid in the urine and reabsorbing bicarbonate—a base that helps stabilize acids—into the blood.
On the other side are the lungs, which are responsible for gas exchange. This means they make sure there is enough oxygen delivered throughout the body and that you are exhaling carbon dioxide (an acidic waste product produced by your cells as they generate energy).
Together, the lungs and kidneys talk to one another to ensure proper balance is maintained but also help each other out in the case of injury. For example, if someone has a respiratory disorder, such as asthma or pneumonia, they are not exhaling carbon dioxide properly. In this case, acidosis will occur due to the extra hydrogen ions floating around in the blood. However, the kidneys can sense this disturbance and effectively increase the amount of acid they excrete and the bicarbonate the body reabsorbs to neutralize the excess carbon dioxide. Think of this like you’re adding more weight (or bicarbonate) to the right side of the seesaw to help it rebalance.
How exactly these two organs can communicate and respond to one another is still under being studied, but hopefully in coming years scientists and researchers will have a better idea of how the seesaw works.
Eva Gilker, MS, is a PhD student in physiology and biophysics at Case Western Reserve University in Ohio. Her research focuses on acid-base balance, specifically how the kidneys sense and respond to elevated carbon dioxide.