vermiform appendix

Vermiform Appendix
Arteries of cecum and vermiform appendix. (Appendix visible at lower right, labeled as "vermiform process").
Normal location of the appendix relative to other organs of the digestive system (frontal view).
Latin	appendix vermiformis
Gray's	subject #249 1178
System	Digestive
Artery	appendicular artery
Vein	appendicular vein
Precursor	Midgut
MeSH	Appendix
Dorlands/Elsevier	a_54/12147735

In human anatomy, the vermiform appendix (or appendix, pl. appendices) is a blind ended tube connected to the cecum, from which it develops embryologically. The term "vermiform" comes from Latin and means "wormlike in appearance". The cecum is a pouch-like structure of the colon. The appendix is near the junction of the small intestine and the large intestine.

Size and location

The appendix averages 10 cm in length, but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The longest appendix ever removed measured 26 cm. ^[1]

The appendix is located in the lower right quadrant of the abdomen, or more specifically, the right iliac fossa.^[2] Its position within the abdomen corresponds to a point on the surface known as McBurney's point (see below). While the base of the appendix is at a fairly constant location, 2 cm below the ileocaecal valve ^[2], the location of the tip of the appendix can vary from being retrocaecal (74% ^[2]) to being in the pelvis to being extraperitoneal. In rare individuals with situs inversus, the appendix may be located in the lower left side.

Function

Given the appendix's propensity to cause death via infection, and the seeming perfect health of those who have had their appendix removed, the biological purpose of the appendix has mystified scientists for some time. There have been cases of people who have been found, usually on laparoscopy or laparotomy, to have a congenital absence of their appendix. There have been no reports of impaired immune or gastrointestinal function in these people.

Historical Interpretation: Vestigiality

The most common explanation is that the appendix is a vestigial structure with no absolute purpose. In The Story of Evolution, Joseph McCabe argued thus:

The vermiform appendage—in which some recent medical writers have vainly endeavoured to find a utility—is the shrunken remainder of a large and normal intestine of a remote ancestor. This interpretation of it would stand even if it were found to have a certain use in the human body. Vestigial organs are sometimes pressed into a secondary use when their original function has been lost.

One potential ancestral purpose put forth by Darwin^[3]: that the appendix was used for digesting leaves as primates. Over time, we have eaten fewer vegetables and have evolved, over millions of years, for this organ to be smaller to make room for our stomach.

The appendix is more developed in Old World monkeys.^[4]

Recent Interpretation: Immune Use

Loren G. Martin^[5], argues that the appendix has a function in fetuses and adults. Endocrine cells have been found in the appendix of 11 week old fetuses that contribute to "biological control (homeostatic) mechanisms." In adults, Martin argues that the appendix acts as a lymphatic organ. The appendix is experimentally verified as being rich in infection-fighting lymphoid cells, suggesting that it might play a role in the immune system. A. Zahid^[6] suggests that it plays a role in both manufacturing hormones in fetal development as well as functioning to 'train' the immune system, exposing the body to antigens in order that it can produce antibodies. He notes that doctors in the last decade have stopped removing the appendix during other surgical procedures as a routine precaution, because it can be successfully transplanted into the urinary tract to rebuild a sphincter muscle and reconstruct a functional bladder.

Researchers at Duke University propose that the appendix serves as a safe haven for useful bacteria when illness flushes them from the rest of the intestines, a function that would be useful in sparsely populated areas where people would be less likely to pass these germs to one another.^[7] This would explain the strong immune activity and the apparent health of those without one in developed countries- potentially in combination with the possibility that strong antibiotics prevent us from using the appendix for the reason it developed.

Diseases

The most common diseases of the appendix (in humans) are appendicitis and carcinoid tumors. Appendix cancer accounts for about 1 in 200 of all gastrointestinal malignancies. Adenomas also (rarely) present.

Appendicitis (or epityphlitis) is a condition characterized by inflammation of the appendix. Virtually all cases of Appendicitis require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, the appendix will rupture, leading to peritonitis, then shock, and, if continued untreated, death. Pain often begins in the center of the abdomen where the lining of the stomach is irritated then moves lower right as the condition develops, it is important to note that this makes diagnoses difficult in the early stages because only an MRI can detect it. Appendicitis presents as pain in the right lower quadrant with rebound tenderness (pain upon removal of pressure rather than application of pressure). In particular, it presents at McBurney's point, 1/3 of the way along a line drawn from the Anterior Superior Iliac Spine to the Umbilicus. Typically, point (skin) pain is not present until the parietal peritoneum is inflamed as well. Fever and immune system response are also characteristic of appendicitis. It is important to see a physician if stomach pain is present.

The surgical removal of the vermiform appendix is called an appendicectomy (or appendectomy). This procedure is normally performed as an emergency procedure, when the patient is suffering from acute appendicitis. In the absence of surgical facilities, intravenous antibiotics are used to delay or avoid the onset of sepsis; it is now recognized that many cases will resolve when treated non-operatively. In some cases the appendicitis resolves completely; more often, an inflammatory mass forms around the appendix. This is a relative contraindication to surgery.

Additional images

Location of McBurney's point (#1)	The superior mesenteric artery and its branches.	The lymphatics of cecum and vermiform process from behind.	Lymphatics of colon.
Superior ileocecal fossa.	Inferior ileocecal fossa.	Interior of the cecum and lower end of ascending colon, showing colic valve.	Mucinous adenocarcinoma of the appendix tip

See also

• Homology (biology)
• McBurney's point

References

External links

• "The vestigiality of the human vermiform appendix: A Modern Reappraisal" -- evolutionary biology argument that the appendix is vestigial
• SUNY Labs 37:12-0102 - "Abdominal Cavity: The Cecum and the Vermiform Appendix"

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