Exogenous Vs. Endogenous: What’s The Difference?

The terms exogenous and endogenous have two different major definitions. One is used in statistics and refers to exogenous and endogenous variables, and the other is in medicine. The words have similar meanings in both contexts; however, their exact definition ends up being different.

In statistics, there are endogenous variables and exogenous variables. To get an idea of what this means, you have to look at the prefix of the words. End-, or less commonly, endo- means within or inside, or taking in. In this case, it’s the former definition of within.

Endogenous, therefore, means within a system. So, an endogenous variable is a variable inside the system, or rather, a variable that is affected by the other variables in the model.

Exogenous is the opposite. As exo- means outside, exogenous means something outside the system. Therefore an exogenous variable is a variable unaffected by the other variables in the model.

For medicine, it’s much the same. Endogenous is something inside the system – in this case, the body – and endogenous is something outside of it. This is most often used in reference to antigens. It’s used to describe similar ailments with different root causes. For instance, there are both endogenous depression and exogenous depression.

Key Takeaways:

What Does Exogenous Mean?

Merriam-Webster defines exogenous as “caused by a factor, or an agent, from outside the organism or system.” It can also mean “introduced from or produced outside the organism or system,” especially if the system or organism itself doesn’t create it. There’s also a botany definition, but that’s beyond the scope of this article.

In statistics, an exogenous variable is a variable that isn’t affected by the other variables. This is often used in economic models such as supply and demand, as well as in agriculture. Here is an example.

In an agricultural model, you will have several variables if you’re looking to determine the factors that contribute to crop yield. You’ll look at the amount of fertilizer used, the type of soil, and how much rainfall there was that year. The exogenous variable will be rainfall because nothing that you do within the model will affect how much or often it rains.

In medicine, exogenous is used to refer to something outside the body – typically something that has an adverse effect on your health. This is why it’s most often used to refer to antigens.

Antigens are anything that generates an immune response. They can be bacteria, fungi, viruses, or allergens. Whatever they are, however, they have to come from outside your body to be considered exogenous antigens.

The word exogenous has been in the language for quite some time, first being recorded in 1830 in its botany definition. It has a Greek origin but was taken directly from the French ‘exogène’, meaning exogenous.

The French word combined the prefix exo– with –’gène,’ which came from Greek; it was taken from their ending –genēs, which means born. Therefore, breaking it down into its parts roughly means something born outside.

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What Does Endogenous Mean?

Endogenous is defined as something “caused by factors inside the organism or system” or something “produced or synthesized within the organism or system.” Therefore, something that’s endogenous is affected by or created inside the system or body. This can be hormones, antibodies, or even something non-chemical, such as your circadian rhythm.

In terms of statistics, an endogenous variable is a variable that’s affected by the other variables in the system. If you’re looking at an economic model, say, then you’d look at the variables in determining income.

You’d consider your salary, health care plan, investments, and tax rate. The endogenous variables are your salary, healthcare plan, and investments because all of these are affected by one another – they’re all part of your salary package. The tax rate, however, is static – it doesn’t change if the other variables do.

In medicine, an endogenous antigen is something that comes from within the body and generates an immune response. This is most often seen in autoimmune conditions. You can also get an endogenous infection or something that usually lives in your body that makes you sick, most often a bacterium.

There are uncountable bacteria that live inside the human body, but sometimes the system will get out of balance, and there’ll be too many – or too few – of a type of bacteria, and that will cause illness.

As with exogenous, the first recorded usage of endogenous was in 1830, also in its botany definition. The two words are very similar to one another; however, endogenous uses the endo- prefix rather than the exo- prefix.

Endo- comes from Greek, meaning inside or within. This is opposed to the Latin-based prefix inter-, which means the same thing; it’s just pulled from a different language.

Endogenous also has an adverb form, endogenously, and a noun from, endogeneity, which means “endogenous quality or origin.” That means that if you ever want to talk about something that’s endogenous, you have several different ways to use the word.

You can see the Greek prefix endo– used in terms like endoskeleton – or an interior skeleton, as mammals have – or an endoscope, which is used to look inside organs.

Exogenous vs. Endogenous FAQ

1. How come a model is able to predict the value of the endogenous variable?

   Models are able to predict the values of endogenous variables because endogenous variables are affected by the values of the other variables in the model. This allows for being able to determine what the other values of the variables are, so long as you understand the interaction between the different variables.

2. What’s the difference between an exogenous antigen and an endogenous antigen?

   The difference between an exogenous antigen and an endogenous antigen is its origin. An exogenous antigen is going to come from outside the body, hence the exo-. Most agents are exogenous, which causes the body to react to them as foreign.

   An endogenous antigen, on the other hand, will come from or be synthesized from inside the body. This is much less common.

3. What is an endogenous change?

   An endogenous change is a change that happens from inside the model. The changing of one endogenous variable is going to inherently alter the other endogenous variables.

   While your outside actions affect change on one of the variables, the others are altered on the system itself, making the change endogenous – or from inside the system.

4. What’s the difference between endogenous budding vs. exogenous budding?

   The difference between endogenous and exogenous budding is that one develops on the exterior of the mother cell, plant, or organism, and the other develops on the interior. This type of budding isn’t the typical one most people think of in terms of flowers, but rather gemmae.

   Exogenous budding is a type of asexual reproduction where a smaller version of the main plant grows on the outside of it and then detaches to form a new individual. This is the most common type of gemma. Animals in the genus hydra reproduce this way.

   Endogenous budding is the same concept, except that instead of forming on the outside of the parent, it forms on the inside. Once the gemma is formed enough, it exits the parent sponge, becoming a new individual. This type of reproduction is seen in sea sponges.

Author

Di Doherty

Di has been a writer for more than half her life. Most of her writing so far has been fiction, and she’s gotten short stories published in online magazines Kzine and Silver Blade, as well as a flash fiction piece in the Bookends review. Di graduated from Mary Baldwin College (now University) with a degree in Psychology and Sociology.