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The large intestine is approximately 1.5 meters in length.
Subdivided into the cecum, ascending, transverse, descending, sigmoid colon and rectum.
The sigmoid begins at the pelvic brim and becomes the rectum at the level of the third sacral vertebra.
The rectum passes between the crura of the peroneal muscles to become extraperitoneal.
Reflection of the peritoneum from the rectum over the pelvic floor creates the pouch of Douglas, a cul de sac.
Approximately 400 species of bacteria are known to be present in the colon.
Normally contains over 1 billion bacteria.
Most colonic bacteria are obligate anaerobes and are extremely oxygen sensitive.
Of the 1-1.5 liters presented to it daily from the small intestine only 100-200 mL/day are present in the final stool output.
Signaling pathways essential for regulation of colonic epithelial growth, include epidermal growth factor growth factor receptor, RAS/RAF/MAPK cascade, and phoshoinositide 3’kinase (PI3K)/Akt.
Normal colonic motility requires integration of myogenic, neural, and hormonal factors.
While the enteric nervous system is independent, it is connected to the central nervous system by sympathetic and parasympathetic nerves.
The targets of the enteric neurons are muscle cells, secretory cells, endocrine cells, microvasculature, and inflammatory cells.
The neurons in the enteric plexuses are stimulated by a food bolus, which distends the gut and stimulates its mucosal surface, leading to the release of factors that stimulate interneurons.
The stimulated interneurons transmit excitatory signals proximally, which cause contraction of the colon and inhibitory signals distally, and these in turn cause relaxation.
These signals are transmitted by the neurotransmitters acetylcholine and serotonin.
The right side of the colon embryologically arises from the midgut.
The proximal colon receives its main blood supply from the superior mesenteric artery.
The left side of the colon arises from the hind gut.
The left, distal colon, arises from the hind gut and supplied by inferior mesenteric artery.
The transverse colon arises from both the midgut and hindgut, but more from the midgut.
Studies have suggested patients undergoing elective colorectal surgery demonstrated no difference in wound infections or anastomotic leakage rates between groups of participants who received or did not receive mechanical bowel preparation.
Some studies showed that the combination of oral antibiotics with a mechanical bowel preparation regimen reduces rates of infection and anastomotic leakage, while others have not demonstrated a significant difference.