Notes from the Video

What You're Going to Learn from This Video on The Appendix

As a surgeon one of the most common operations I do every week is a laparoscopic appendectomy...removing a child's appendix.

Very often I'm asked the questions...why do we have an appendix?  What is the appendix?  What does the appendix do?

In this talk I'm going to teach you a few things you probably didn't know about the appendix!

1.). The Appendix as a Bacterial Reservoir

2.). The Appendix as a Biofilm Producer

3.). The Appendix and the Immune System

What is the appendix?

The appendix is a small, wormlike organ located at the junction of the small intestine and large intestine.  The appendix is also called vermiform for it's worminess. 

In terms of its dimensions, the appendix can vary in size among individuals, but on average, it measures approximately 2 to 4 inches (5 to 10 centimeters) in length. The diameter of the appendix is usually less than 7mm.

The blood supply to the appendix is from the superior mesenteric artery which gives off the ileocolic artery and then the appendices artery with segmental branches to the appendix.

The histologic structure of the appendix is also important to understand, especially considering its immune importance.

The histologic structure of the appendix consists of several layers that are similar to those of the rest of the gastrointestinal tract. The layers, from the innermost to the outermost, include:

Mucosa: The mucosa is the innermost layer of the appendix. It is lined by a specialized type of epithelial tissue called simple columnar epithelium, which contains mucus-secreting goblet cells. The mucosa also contains numerous lymphoid follicles, which are clusters of lymphoid tissue involved in immune responses.

Submucosa: The submucosa is a connective tissue layer located beneath the mucosa. It contains blood vessels, lymphatic vessels, and nerves that supply the appendix.

Muscularis externa: The muscularis externa is composed of two layers of smooth muscle: an inner circular layer and an outer longitudinal layer. These muscle layers play a role in propelling contents through the appendix.

Serosa: The serosa is the outermost layer of the appendix. It is a thin, protective layer composed of connective tissue and a layer of simple squamous epithelium called mesothelium. The serosa covers the appendix and helps to anchor it to surrounding structures.

The Appendix and Bacteria

While the appendix itself does not play a major role in digestion, it may have an impact on the gut microbiota and offer potential benefits for the commensal bacteria in the colon.

Bacterial reservoir: The appendix can serve as a reservoir for beneficial bacteria. In cases of severe diarrhea or gastrointestinal infections that result in a loss of gut flora, the appendix may act as a source for replenishing the gut microbiota.

Microbial diversity: The appendix contributes to the overall microbial diversity within the gut. The presence of diverse microbial species is associated with a healthy gut microbiome, and the appendix can add to this diversity. Studies have shown that the bacterial composition in the appendix is distinct from other regions of the digestive tract, suggesting that it may harbor unique bacterial species.

Immune system support: The presence of bacteria in the appendix can play a role in immune system regulation. The immune tissue in the appendix, such as lymphoid follicles, may interact with the gut microbiota and help train the immune system to distinguish between harmful pathogens and beneficial commensal bacteria. This interaction can contribute to immune system development and maintenance.

Resilience to infections: It has been proposed that the appendix may have a role in protecting against certain infections. The presence of beneficial bacteria in the appendix may enhance the body's ability to fight off harmful pathogens. By acting as a reservoir for beneficial bacteria, the appendix could aid in repopulating the gut microbiota after an infection, helping to restore a healthy microbial balance.

What type of bacteria are present in the appendix?

Bacteroides: Bacteroidetes is a phylum of bacteria that includes various species such as Bacteroides fragilis, Bacteroides uniformis, and Prevotella species.  Bacteroidetes are commonly found in the human gut, including the appendix, and play a role in the degradation of complex carbohydrates and the production of short-chain fatty acids.

Firmicutes: Firmicutes is another phylum of bacteria that encompasses diverse species, including Clostridium and Ruminococcus. Some species within Firmicutes are associated with carbohydrate metabolism and the production of beneficial metabolites like butyrate.

Proteobacteria: Proteobacteria is a phylum that includes several well-known genera such as Escherichia coli and Klebsiella. These bacteria can have both commensal and pathogenic strains. Proteobacteria are found in various regions of the gastrointestinal tract, including the appendix.

Actinobacteria: Actinobacteria, including the genus Actinomyces, can be present in the appendix. Actinobacteria are known for their diverse metabolic capabilities and can have both beneficial and opportunistic pathogenic strains.

Fusobacteria: Fusobacteria, specifically the species Fusobacterium nucleatum, have been detected in the appendix. Fusobacteria are commonly found in the oral cavity and have been associated with oral infections, but their presence in the appendix is not yet fully understood.

What is the relationship between colonic biofilm and the appendix?

Biofilms are complex microbial communities that can form on various surfaces in the body, including the colon. They consist of microorganisms, such as bacteria, embedded in a matrix of extracellular polymeric substances (EPS). Biofilms in the colon have been studied extensively and have been associated with various aspects of gut health and disease.

It has been suggested that the presence of biofilms within the appendix could play a role in its function. The appendix has been proposed to act as a reservoir for beneficial bacteria, and the formation of biofilms could help support the colonization and stability of these bacteria within the appendix.

Biofilms can provide a protective environment for bacteria, shielding them from host immune responses and external influences.

Additionally, biofilms within the appendix may contribute to the overall diversity and stability of the gut microbiota.

Biofilm formation can facilitate the coexistence and interactions between different bacterial species, promoting a balanced microbial community. This diversity and stability of the gut microbiota are essential for maintaining gut health and preventing dysbiosis.  Disrupted biofilms or alterations in the microbial composition within the appendix may impact the overall microbial balance, potentially leading to inflammation and subsequent appendicitis.

How does the appendix impact inflammatory bowel disease?

Research has suggested that individuals who have undergone an appendectomy (surgical removal of the appendix) may have a slightly lower risk of developing ulcerative colitis but a potentially increased risk of developing Crohn's disease.

This may be due to a direct immune and inflammation effect or a consequence of the microbiome.

What are the most common tumors of the appendix?

The appendix is an interesting organ with respect to cancer as there are some unique cancers that can originate from the appendix.

The most common tumors of the appendix are:

Carcinoid tumors: Carcinoid tumors are the most common type of tumors that occur in the appendix. They arise from neuroendocrine cells, which are specialized cells that produce hormones. Carcinoid tumors in the appendix are often slow-growing and may or may not cause symptoms. Most carcinoid tumors of the appendix are benign, but a small percentage can be malignant.

Mucinous adenocarcinomas: Mucinous adenocarcinomas are a type of cancer that arises from the glandular cells lining the appendix. They are characterized by the production of excess mucus. Mucinous adenocarcinomas of the appendix can be aggressive and may spread to other parts of the body.

Non-mucinous adenocarcinomas: Non-mucinous adenocarcinomas are another type of cancer that can occur in the appendix. They arise from the glandular cells and can be aggressive.

Goblet cell carcinoid: Goblet cell carcinoid tumors are rare tumors that have features of both carcinoid tumors and adenocarcinomas. They are characterized by the presence of both neuroendocrine cells and glandular cells.

Goblet cell carcinoids are typically more aggressive than typical carcinoid tumors.

It is important to note that the majority of appendix tumors are benign, particularly carcinoid tumors. Malignant tumors, including adenocarcinomas, are less common but may have a more aggressive course. T