Caecum And Appendix

Structure and Function

Structure

They lie in the right ilac fossa. The ileocaecal valve, protruding into the large intestine, marks the upper border. The vermiform appendix is around 10-15cm long, and is connected by a slit like opening. It has its own little mesentery, the mesoappendix, attached to the small intestine's mesentery.

On the outside wall of the caecum are the taenaie, which look like cords running down the outside. At the apex of the caecum they form a Y style join (as in three coming in to one point).

Functions

Hmm. Well, it is the point where stuff begins to turn from liquid to solid, as it starts its journey around the colon.

I think I read in Snell that its in this area some animals produce cellulose digesting enzymes, though that may well be somewhere else. There is no real purpose for the appendix. It probably is linked to immune response in some way, hence all the lymphoid tissue.

Arterial and Venous supply

Nervous Supply

That's right, you guessed it! VAGUS?! WOOOOHOOOOO! As a bonus, the appendix has afferent nerve fibres concerned with the conduction of visceral pain from the appendix, travel with the sympathetic nerve and enter the spinal cord at level t10.

Lymph

Ultimately, they drain into the superior mesenteric nodes.

Histology

Similar to the small intestine it has an columnar epithelium of mature enterocytes and goblet cells with scattered entero-endocrine and paneth cells, following the same basic intestinal layers, however there are some key differences.

• No villi or deep crypts.
• No plicae
• There are large sacculations (no idea)
• Strips of longitudinal muscle in the muscularis externae, called taenia coli, which run along the bowel and combine at the apex of the caecum.
• Fat pads attaching to the serosal surface called the appendices epiploica.

The appendix has a colonic histology, aside from the fact that it generally contains more lymphoid tissue.

Clinical Conditions

Appendicitis

About: This is the most common surgical emergency. There are theories why it happens including carcinoid tumours and lymphoid hyperplasia. However it is most commonly caused by presence of (and obstruction by) faecoliths (hard pellets of poo, after dehydration). Also caused generally by low fibre diets. Can also be involved with ulcerative colitis and Crohn's disease.

Presentation: Classically presents as vague referred pain in the region of the umbilicus with no apparent cause, that suddenly localises and intensifies to the right iliac fossa. Nausea, vomiting and diarrhoea occur. Can be confused with Meckel's diverticulum, or other acute inflammations such as Crohn's.

Investigations: Ultrasound is effective, CT perfect.

Treatment: Surgery, often via laparotomy