Boundaries and general contents
The anatomical space of the lower floor is bounded superiorly by mesocolon transversum (the transverse mesocolon) and transitions inferiorly into the pelvic cavity.
The contents of this region include:
- The small intestine, starting from the inferior part of the duodenum (including the jejunum and ileum).
- Various parts of the large intestine.
Peritoneal relief and mesentery of the small intestine
The complex peritoneal relief is formed by the sites of its transition from the body walls to the internal organs. This results in the formation of:
- Two mesenteric sinuses;
- Two lateral canals;
- Five recesses (recessus).
The posterior abdominal wall is connected to the jejunum and ileum by mesenterium, a wide and strong peritoneal duplicature. The root of the mesentery divides the subcolic space into two mesenteric sinuses.
Anatomical structures of the lower region
A detailed examination of the anterior view of the lower floor organs reveals the following key anatomical elements:
- Colon ascendens (ascending colon) and Colon descendens (descending colon);
- Caecum (cecum) with Appendix vermiformis (appendix) and its mesentery (mesoappendix);
- Intestinum ileum (ileum);
- The ileocecal junction, including the superior and inferior ileocecal recesses (recessus ileocaecalis superior et inferior), as well as the corresponding folds (plica ileocaecalis superior et inferior);
- Colon sigmoideum along with its mesentery (mesocolon sigmoideum);
- Rectum (rectum), urinary bladder (vesica urinaria), pelvic cavity (cavum pelvis), and rectovesical fold (plica rectovesicalis).
Peritoneal recesses and clinical significance
Particular attention in topographic anatomy is paid to peritoneal recesses (pockets). These anatomical formations represent weak points of the abdominal cavity. It is in these areas, under certain pathological conditions, that internal hernias can form.
Briefly: answers to topical questions
What exactly are the five pouches (recessus) of the peritoneum identified in the lower floor of the abdominal cavity?
Five peritoneal recesses (pockets) are distinguished in the lower floor of the abdominal cavity, which are potential sites for the formation of internal hernias.
- Treitz's recess (recessus duodenojejunalis) — located in the region of the duodenojejunal flexure.
- Superior ileocecal recess (recessus ileocaecalis superior) — bounded by the superior ileocecal fold.
- Inferior ileocecal recess (recessus ileocaecalis inferior) — bounded by the inferior ileocecal fold.
- Retrocecal recess (recessus retrocaecalis) — located posterior to the cecum.
- Intersigmoid recess (recessus intersigmoideus) — located in the region of the sigmoid colon, bounded anteriorly by its mesentery.
What are the anatomical boundaries of the right and left mesenteric sinuses?
The anatomical boundaries of the mesenteric sinuses are defined by the transverse mesocolon, parts of the colon, and the root of the small intestine mesentery.
| Sinus | Superior boundary | Lateral boundary | Medial and inferior boundaries |
|---|---|---|---|
| Right mesenteric sinus (sinus mesentericus dexter) | Transverse mesocolon | Ascending colon | Left and inferiorly — mesentery of the small intestine and the terminal ileum |
| Left mesenteric sinus (sinus mesentericus sinister) | Transverse mesocolon | Descending colon | Right — mesentery of the small intestine |
What limits the right and left lateral canals (canalis lateralis) of the abdominal cavity?
The lateral canals of the abdominal cavity are bounded by the lateral abdominal walls and the corresponding parts of the colon.
- Right lateral canal (canalis lateralis dexter) — located between the lateral abdominal wall and the ascending colon.
- Left lateral canal (canalis lateralis sinister) — located between the left lateral abdominal wall and the descending colon. Superiorly, this canal is bounded by the phrenicocolic ligament (lig. phrenicocolicum), which separates it from the left subphrenic space.
Which organs of the lower floor of the abdominal cavity are covered by peritoneum intraperitoneally?
In the lower floor of the abdominal cavity, the following organs are covered by peritoneum intraperitoneally (on all sides):
- Small intestine (intestinum tenue) — jejunum and ileum.
- Cecum (caecum) — covered on all sides in 97% of cases.
- Appendix (appendix vermiformis).
- Sigmoid colon (colon sigmoideum).
- Rectum (rectum) — only its upper part.
Transverse colon (colon transversum) is also covered intraperitoneally, but it serves as the boundary between the floors.
Which parts of the large intestine are located in the lower floor of the abdominal cavity?
The following parts of the large intestine are located in the lower floor of the abdominal cavity:
- Cecum (caecum) with the vermiform appendix (appendix vermiformis).
- Ascending colon (colon ascendens).
- Descending colon (colon descendens).
- Sigmoid colon (colon sigmoideum).
- Rectum (rectum) — its pelvic part.
The transverse colon (colon transversum) and its mesentery serve as the upper boundary of the lower floor; therefore, its contents include the parts lying below this boundary.
Class and exam questions
What serves as the upper and lower boundaries of the lower floor of the abdominal cavity?
Above, the floor is bounded by the transverse mesocolon (mesocolon transversum), and below, by the cavity of the lesser pelvis.
What elements form the peritoneal relief in this region?
The relief is formed by two mesenteric sinuses, two paracolic gutters, and five recesses (recessus).
What is the clinical significance of peritoneal recesses?
Peritoneal recesses are weak points where internal hernias may form.
What else to study on this topic
- Topography of the mesenteric sinuses and paracolic gutters
- Structure and anatomical variants of the root of the mesentery of the small intestine
- Detailed analysis of ileocecal recesses and folds
- Mechanisms of internal hernia formation in peritoneal recesses
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