Cecum

The appendix (Latin caecum, coecum or cecum, or intestinum caecum, from which is derived the technical term caecum or coecum or. German Zäkum oder Zökum; Greek τυφλὸν ἔντερον typhlon enteron from τυφλός typhlos, German 'blind' and ἔντερον enteron, German 'intestine') is the blind-ending initial part of the large intestine, which protrudes downwards into the abdominal cavity in the shape of a sac at the end of the small intestine.

While the human appendix, which is located in the right mid-abdomen and is six to eight centimeters long, is rather small, many herbivores have a sack-like elongated appendix. This is especially the case in those herbivorous mammals that are unable to process their highly cellulosic food by rumination. A warm-blooded domestic horse, for example, has a caecum one metre long and with a capacity of about 30 litres.

In most mammals, the appendix is located on the right side of the abdominal cavity; however, Old World pigs are an exception, in which it is located on the left.

In birds, the appendix is paired. In chicken and duck birds, the two appendixes are relatively long and also perform digestive functions, while in many pigeon, parrot and sparrow birds they are rudimentary.

Function

The common assumption that the appendix has no function in humans has been disproved by studies. The appendix has abundant lymphatic tissue in most species, especially in those with poorly developed digestive function. Therefore, the appendix also has a major role in mediating immunity processes to antigens ingested through the digestive tract. It is thus considered part of the immune system. In addition, there is the theory that after diarrhoea the "emptied" intestine is repopulated with intestinal bacteria starting from the appendix.

Herbivores, which are not ruminants, have a highly developed appendix to convert non-cleavable organic nutrient compounds in the feed into absorbable nutrients with the help of nutrient-cleaving microorganisms. Examples in the animal world include horses, rhinoceroses, tree shrews, and rodents such as guinea pigs.

Anatomy in humans and other primates

The lower end of the appendix can be marked in primates with a line drawn from the navel to the right anterior superior iliac spine, on which the so-called McBurney point is located between the outer and the middle third of the line. Here - at the point where three longitudinal strips (taenia) of the appendix, consisting of smooth muscle, also meet - lies the exit point of the appendix (lat.: the appendix vermiformis).

The lower end of the ileum (scrotum) protrudes into the appendix as an ileocecal valve or Bauhin's valve. When the appendix is stretched, this valve prevents bacteria from entering the small intestine, the lower part of which is the ileum.