Why the appendix is much more important than we once thought

You may have heard that astronauts have their appendix removed before leaving Earth. After all, people say you can live without this organ because it serves no purpose, but how much truth is there in this belief?

Let’s start by locating it. The appendix is a small, finger-shaped pouch located where the small intestine joins the large intestine, in the cecum. Inflammation and infection of the appendix, known as appendicitis, can lead to rupture of the organ and subsequent widespread infection (peritonitis). If left untreated, it can become life-threatening.

On some long-term missions to remote and isolated areas—such as Antarctica or outer space—participants were previously required to undergo appendix removal surgery (appendectomy) before departure. This was justified by the limited access to medical facilities and the difficulties in evacuating people from these remote areas in the event of a medical emergency.

Removing the appendix prior to departure eliminated any risk of appendicitis and its associated complications during the mission, thus helping to ensure the safety and well-being of those involved. Apparently, there were no downsides, though we now know that it is not the case.

A vestigial organ

For our ancestors, the appendix most likely evolved to help them digest a diet rich in raw vegetables and cellulose, as it still does in many herbivorous mammals. Thousands of years ago it would have functioned as an extension of the cecum, involved in the bacterial digestion of fibrous plant materials.

As the human diet diversified, becoming richer in animal proteins and more digestible cooked or fermented foods, there was less need for a bulky cecum and a functional appendix to digest cellulose. As a result, the human appendix reduced in size and lost its original digestive function. For this reason, it has long been considered a vestigial organ, a part of the body that was useful at the time but that we can do without today.

However, while it no longer serves its original purpose, we now know that the appendix has evolved new functions that are essential for human health.

A microbiome regulator

The appendix has been shown to be an important component of immune function, especially in early life. It acts as a lymphoid organ similar to Peyer’s patches in the intestine, and contributes to the maturation of B lymphocytes (a variety of white blood cell) and the production of antibodies (type A immunoglobulin), which are crucial for controlling the density and quality of the intestinal microbiota.

In addition, the appendix itself contains a very diverse and varied microbiota, including bacteria such as Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Fusobacteria. This diversity is distinct from other parts of the gastrointestinal tract, suggesting a specialized role.

Removal of the appendix has been associated with a reduction in gut bacterial diversity. People who have undergone an appendectomy show a reduced amount of beneficial short-chain fatty acid-producing bacteria, including Roseburia, Barnesiella, Butyricicoccus, Odoribacter and Butyricimonas. This reduction in microbial diversity can lead to intestinal dysbiosis, and potentially increase susceptibility to various diseases.

Appendectomy has also been linked to an increase in fungal diversity in the gut. This change in the microbial ecosystem suggests that the appendix may play a role in the balance between bacterial and fungal populations, potentially acting as a store of commensal gut microbiota that repopulate the colon after exposure to pathogens or antibiotic treatment.

The appendix may play a further role in protecting the gastrointestinal system from invading pathogens. This would explain why surgical removal of the appendix has been associated with a worse prognosis for recurrent infection with Clostridioides difficile, and an increased risk of inflammatory bowel disease and ulcerative colitis.

It may even be related to the increased incidence of other conditions such as heart disease and Parkinson’s disease. The role of the appendix in maintaining microbial diversity therefore appears to be critical to overall health.

What about the astronauts?

Although removal of the appendix was until recently quite a routine procedure, we cannot ignore its potential risks.

First of all, there are the risks inherent to any surgery—postoperative infections can occur in any surgical procedure, and appendectomies are no exception. Hemorrhage is another possible complication that may arise during or after removal, and in rare cases, postoperative bleeding may require blood transfusions. Moreover, an appendectomy is usually performed under general anesthesia, which carries its own set of additional risks.

But as we have just seen, the appendix also plays a significant role in regulating the gut microbiome, contributing to its diversity. This is why removal as a preventive measure is no longer recommended for astronauts. NASA is aware that the potential risks associated with such an intervention outweigh its benefits, and prefers to focus on maintaining astronauts’ overall health while providing the necessary medical support during space missions.

This article is republished from The Conversation under a Creative Commons license. Read the original article.