Vermiform appendix

General structure plan and anatomical position

Anatomically, the vermiform appendix originates from the medial-posterior surface of the cecum. Its origin point is located approximately 2.5–3.5 cm below the ileocecal junction.

Histologically, the organ wall retains the basic structural plan of the digestive tube. Four classic layers are clearly distinguishable:

1. Mucosa (mucous membrane).
2. Submucosa (submucosal layer).
3. Muscular layer (muscularis externa).
4. Serosa (serous membrane).

The uniqueness of the appendix lies in the fact that its tissues intricately combine elements of the large and small intestine, supplemented by its own highly specific structures.

Differential diagnosis: differences from the intestine

To accurately identify the appendix on a histological slide, it is important to understand how it differs from other parts of the gastrointestinal tract. The organ demonstrates reduced features of the large intestine, but lacks a number of its classic attributes, which structurally brings it closer to the small intestine.

Signs of the large intestine in the appendix:

• Villi are completely absent from the mucosal relief.
• Crypts (epithelial invaginations) are preserved.
• The epithelium remains simple columnar. Important nuance: the brush border (microvilli) is practically unexpressed here and lacks the characteristic oxyphilia, which distinguishes it from the actively functioning epithelium of other zones.

Similarities with the small intestine (differences from typical large intestine):

• There is no predominance of goblet cells in the epithelial layer (their number is noticeably smaller than in the colon).
• The outer layer of the muscular layer runs in a continuous ring and does not divide into longitudinal bands (taeniae).
• Haustra and fixed semilunar folds do not form in the wall.
• Fatty appendices (appendices epiploicae) are absent on the serosa.

> Practical tip: Under a microscope, macroscopic anatomical features (such as haustra or epiploic appendages) are not visible on a glass slide. Therefore, differential diagnosis is always based on epithelial characteristics and the continuous structure of the muscular layer.

Specific features: "intestinal tonsil"

The main distinguishing feature of the vermiform appendix, allowing it to be recognized instantly, is the colossal development of the lymphoid apparatus. It is this feature that gave the organ its second name.

• Lymphoid aggregates (key feature): Massive lymphatic follicles lie within the lamina propria of the mucosa. This tissue, together with interfollicular accumulations, occupies such a large volume that it extends deep into the submucosa. At the same time, it literally disrupts the muscularis mucosae, which is practically absent in the appendix.
• Age-related changes: The lumen of the appendix is subject to age-related transformations. Over the years, it can completely obliterate (grow shut). In this case, the organ cavity is replaced by proliferating connective tissue.
• Clinical significance: Due to the abundance of lymphoid tissue, inflammation of the appendix (appendicitis) is conceptually compared to inflammation of the palatine tonsils, earning it the name "intestinal quinsy". However, appendicitis harbors a much greater danger: unlike tonsillar quinsy, inflammation of the appendiceal wall threatens perforation with subsequent development of severe peritonitis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Features of the cellular composition of the crypts of the vermiform appendix
• Histophysiology and mechanisms of appendiceal lumen obliteration
• Organization of interfollicular tissue and lymphatic follicles
• Pathomorphological changes of the wall under the risk of perforation

Other topics in the section "Digestive System: Large Intestine, Liver, and Pancreas"

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