Vermiform Appendix
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26-04-2016, 04:00 PM
Vermiform Appendix
The vermiform appendix is an organ localized at the right lower quadrant and has an average size of 8.21cm. It is infamous for causing the most frequent acute surgical condition of the abdomen, appendicitis. Appendicitis can be caused by lymphoid proliferation or by a fecalith impaction.

This organ has been thought to be an evolutionary vestige, because it was thought that it had no function. A vestige is defined as a trace or a rudimentary structure; the degenerated remains of any structure which occurs as an entity in the embryo or fetus.

Through the years it’s been suggested that the appendix has an immune function. The appendix is histologically composed of lymphoid tissue, which produces IgA, an immunoglobulin that helps in immune response. IgA and mucin produced by the appendix is the proposed mechanism in the formation of biofilms. This biofilms are thought to help maintain the presence of commensal bacteria which are an important part in the homeostasis of the gut.

The appendix serves as a “safe house” for bacteria, in case there’s an event such as diarrhea which wipes the colon. Therefore, brings “balance” to the gut flora after the primal infection.

About the immunologic response of the appendix, it seems as it’s more specific to early years of development. The lymphoid tissue of appendix starts to decrease at age 20 until age 60 where there’s very little o null immune function. This might explain why appendicitis is frequently associated with lymphoid proliferation during infancy and not in the elderly, which more frequently present appendicitis due to fecaliths.

This safe house seems important in regions of the world in which there’s a high incidence in GI infections. On the contrary, in developmental countries it might be beneficial for preventing Clostridium dificile infections rather than viral diarrhea (most common cause). Also the presence of an appendix has been linked to a risk reduction in ulcerative colitis incidence, but this needs more studies.
Even though it has some advantages, it still has the great disadvantage of appendicitis. Because its diameter is relatively small and has a small entrance, it makes it difficult to clean out secretions, thus leading to obstruction and subsequent inflammatory response.

Looking at the evidence it looks like the appendix is more an exaptation rather than a vestige. The appendix could have a different function in the past but now it has changed. It could have come from the primordial cecum which was rich in lymphatic tissue and helped to digest cellulose in herbivores.

Exaptation is defined as a biological adaptation where the biological function currently performed by the adaptation was not the function performed while the adaptation evolved under earlier pressures of natural selection.

What do you think about the appendix, is a vestigial organ or an exaptation?

-Ansaloni, L., Catena, F. and Pinna, A. (2009). What Is the Function of the Human Vermiform Appendix? European Surgical Research, 43(2), pp.67-71. doi: 10.1159/000219236
-Barlow, A., et al. (2013). The vermiform appendix: A review. Clin. Anat., 26(7), pp.833-842. doi: 10.1002/ca.22269
-R. Bollinger, et al. (2007). Biofilms in the large bowel suggest an apparent function of the human vermiform appendix. Journal of Theoretical Biology, 249(4), pp.826-831. doi:10.1016/j.jtbi.2007.08.032
-Sarkar, A. (2015). A Glimpse Towards the Vestigiality and Fate of Human Vermiform Appendix-A Histomorphometric Study. JCDR. 9(2), pp.11-15 doi: 10.7860/JCDR/2015/11178.5581

"Skepticism is the first step towards truth" -Denis Diderot
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26-04-2016, 04:23 PM
RE: Vermiform Appendix
I don't know why it got duplicated, could you please erase this thread?

"Skepticism is the first step towards truth" -Denis Diderot
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