The appendix vermiformis is an appendage of the appendix that is prone to acute inflammation. Colloquially, it is also called the appendix. Recent research suggests an immunoregulatory function of the organ previously classified as largely nonfunctional.
What is the vermiform appendix?
Infographic showing the anatomy and location of appendicitis. Click image to enlarge. The appendix vermiformis (appendix vermiformis) is an outpouching composed largely of lymphoid tissue, averaging 10 cm in length and 0.5 mm in diameter, that opens into the appendix (caecum) via a valvular mucosal fold called Gerlach’s valve. The appendix is often incorrectly referred to as the appendix in common parlance. The appendix vermiformis is located in the lower right quadrant of the abdomen as the exit site of the caecum below the ileocecal valve (valva ileocaecalis), the functional closure between the large and small intestines.
Anatomy and structure
In shape, size, and location, the appendix vermiformis is extremely variable; however, it is generally located retrocecally (“behind the caecum”), ascending or descending. The three taenia of the colon continue on the appendix as a closed longitudinal muscle layer. Overall, the appendix vermiformis consists of the following tissue layers (from the inside to the outside): a mucosal layer (tunica mucosa), a connective tissue layer between the mucosa and the muscular layer (tela submucosa), a fine tissue layer containing smooth muscle cells (tunica muscularis), and a serous skin layer (tunica serosa). The serosa enclosing the organ merges into the mesoappendix (mesenteriolum) at the attachment site, which carries the supplying blood vessels (appendicular artery, appendicular vein). The tela submucosa and tunica mucosa contain the Peyer’s plaques. These lymphoid follicle collections protrude dome-like into the appendiceal lumen in some areas. Instead of the usual villi and crypts, M cells are found here. These direct antigens to the lymphoid follicles and trigger an immune response.
Function and tasks
The function of the vermiform appendix has been debated for some time. Despite evidence to the contrary, it was assumed until a few years ago that the appendix was merely a functionless remnant of evolutionary development. In the meantime, it is assumed that it has an immunoregulatory function as a lymphoid organ and is part of the so-called GALT (gut-associated lymphoid tissue), the immune system of the intestine. However, its exact function is not yet clearly understood. The gut-associated lymphoid tissue consists of aggregated lymphoid follicles (Peyer’s plaques) throughout the gastrointestinal tract, which serve as colonies of B lymphocytes for the proliferation and differentiation of B lymphocytes into antigen-producing plasma cells. As part of the acquired immune system, Peyer’s plaques play a significant role in the defense against infection and the processing of immunologically relevant information. In addition, recent studies indicate that in diarrheal diseases, beneficial bacteria of the natural intestinal flora are protected together with molecules of the immune system in the appendix vermiformis from diarrhea-induced washout and are supplied with defense substances by the surrounding lymphatic system. Accordingly, the appendix functions as a kind of “safe house.” During the convalescence phase, the bacteria that survive in this way can recolonize the intestine and displace the germs still present there. This function is particularly significant in areas with poor hygienic context conditions. In developed countries, appendectomy (removal of the appendix as a result of inflammation), which is frequently performed, has not been found to have any effect on the health of the respective affected individuals.
Diseases and medical conditions
Particularly in children of elementary school age and older, as well as young adults, scarred strands, indigestible food components (including fruit stones), or fecal stones can lead to obstruction of the appendiceal lumen. The stagnant secretion damages the wall of the appendix and provides an optimal breeding ground for bacterial pathogens, which can migrate either via the bloodstream or from the intestinal flora (intestinal infections), multiply and cause acute inflammation (appendicitis).Although acute appendicitis is a very common disease and represents the most frequent emergency in abdominal surgery with 7 to 12 percent of cases, early diagnosis is difficult due to the different positional anomalies and the individually very different pain localization. In addition, the classic symptoms such as loss of appetite, pulling as well as colicky pain in the umbilical region or epigastrium (upper abdominal region) with later pain shifting to the lower abdomen, nausea and vomiting as well as moderate fever manifest themselves in only about 50 percent of those affected. The main complication of appendicitis is perforation. In an open perforation, the purulent secretion flows from the appendix into the free abdominal cavity, where it can cause life-threatening diffuse peritonitis (generalized inflammation of the peritoneum) with an increased risk of sepsis. The most common pathogens released include enterococci as well as Escherichia coli, and in rarer cases Salmonella, Staphylo- or Streptococci. A covered perforation results in an abscess covered by the large mesh (perityphlitic abscess) with localized collections of pus in the right lower abdomen (local peritonitis). Even in appendicitis with perforation and peritonitis, the lethality is only 1 percent. In rare cases, malignant tumors may develop in the appendix (appendiceal malignancies).
