Colon
The large intestine' (lat. Intestinum crassum) forms the final lower part of the digestive system. It begins at the transition of the final section of the small intestine (Latin ileum) to the appendix (Latin caecum) and ends at the anus. The main functions of the colon are water reabsorption and thus thickening of the stool. It is also involved in the fine regulation of the electrolyte balance and has a dense bacterial colonization and thus very diverse intestinal flora.
Anatomy
Division
The human colon measures approximately 1.5 meters and is roughly divided into three sections from oral to aboral:
- Appendix (lat. caecum) with vermiform appendix (lat. appendix vermiformis).
- Colon (lat. Colon) with the subsections
- Ascending colon
- Colon transversum
- Descending colon
- Sigmoid colon
- Rectum (lat. rectum)
Projection on the hull
In the ventral view, it can be seen that the colon forms a frame around the loops of the small intestine. The most orally located piece is in the right lower abdomen. Here is the junction of the small intestine via the ostium ileale or the Bauhin valve (small intestine-appendix valve). Caudal to this junction, the large intestine terminates in a factitious duct, the appendix (lat. Caecum) mit dem Wurmfortsatz (lat. Appendix vermiformis). However, the location of the caecum is highly variable.
The colon begins above the caecum. The part ascending towards the liver is called Colon ascendens. After a bend below the liver (Flexura coli dextra) follows the transition into the transverse colon (lat. Colon transversum), which runs horizontally through the abdominal cavity. With the Flexura coli sinistra the transverse colon finally turns again and runs descending as descending colon towards the pelvis. Der anschließende Teil des Colon sigmoideum zieht sich dorsal zum Kreuzbein, biegt dorsal ab und geht schließlich in den Enddarm über, welcher außerhalb der Bauchhöhle liegt. Der Enddarm wird in Mastdarm (lat. Rectum) und Analkanal bzw. After unterteilt.
The rectum as the upper part of the rectum is about 15-16 centimeters long and is located in the small pelvis. Here it extends from the upper edge of the S3 to the perineum (lat. peritoneum). A lateral view shows that the structure of the rectum runs in two curves:
The flexura sacralis lies retroperitoneally and nestles against the concave shape of the sacrum (lat. Os sacrum). The flexura perinealis is already extraperitoneal.
Relationship with neighboring organs
The junction of the final section of the small intestine (Latin ileum) is located end-to-side of the appendix. In direct proximity to it is the transition to the appendix.
The most common intra-abdominal disease requiring surgical intervention is appendicitis (inflammation of the appendix). If this disease is not treated, there is a risk of the inflammation breaking through into the peritoneal cavity. This can result in life-threatening inflammation of the peritoneum.
The kidneys are partially obscured by these colonic segments due to the zones of attachment of the ascending and descending colon to the posterior wall of the peritoneal cavity. The right and left colonic flexures are close to the left and right kidneys because of their retroperitoneal location, but are spatially separated because of the intervening capsula adiposa.
In the male anatomy, the rectum is located behind the urinary bladder and prostate and in front of the sacrum. In female anatomy it is found behind uterus or vagina and in front of the sacrum.
Position In situ
The appendix with appendix, the transverse colon and the sigmoid colon lie intraperitoneally and are attached to the wall of the trunk by a mesocolon. The transverse colon in particular is significantly more mobile than the rest of the large intestine due to its suspension, the mesocolon transversum.
Parts of the colon (ascending and descending colon) lie retroperitoneally and are directly fused to the trunk wall. The same applies to the upper rectum. The end of the rectum and the anal canal lie extraperitoneally outside the abdominal cavity.
The right colonic flexure lies lower than the left flexure due to the right liver lobe taking up more space. The ascending colon lies more ventrally than the descending colon.
The colon also has a characteristic morphology. The longitudinally striated musculature (stratum longitudinale of the tunica muscularis) is not stretched over the entire wall, but forms three separate longitudinal muscle strips, the taenia coli: Taenia libera, Taenia omentalis, Taenia mesocolica. These stretch over all sections of the colon, except for the rectum and vermiform appendix.
Furthermore, there are protrusions of the uppermost wall layer, the appendices omentales on all sections with the exception of the appendix and rectum.
The characteristic bulges of the wall of the colon are called Haustren (lat. Haustra coli). These are delimited by the plicae semilunares coli (transverse folds of the wall). They are formed by contraction of the longitudinally striated musculature and have no fixed localization, but move from oral to aboral direction due to peristalsis.
The rectum as the final part of the colon differs in its morphological characteristics from the rest of the intestine. Here the taenia merge into a continuous longitudinal musculature. Haustren and appendices omentales are not present. The plicae semilunares of the colon merge into three constant plicae transversae recti.
