Colon

Colon . Also called the large intestine , it is the last portion of the digestive system in most vertebrates ; extracts water and salt from solid waste before they are eliminated from the body. It is a long, hollow tube at the end of this system, in which the body produces and stores stool . The ileocecal valve of the ileum ([[small intestine]]) passes the material to the large intestine through the cecum . The material passes through the ascending, descending and transverse portions, and sigmoid of the colon and finally to the rectum . From this waste is expelled from the body.

Table of Contents

Summary

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1 Anatomy
2 Formation of the large intestine
3 Function
4 Sections of the colon
- 1 Ascending colon
- 2 Transverse colon
- 3 Descending colon
- 4 Sigmoid colon
5 Relationships of the portions of the large intestine
6 Irrigation of the large intestine
7 Histology of the large intestine
8 Exploration of the large intestine
9 Diseases of the large intestine
10 Detail of some malformations of the large or medium intestine
11 Reference
12 See also
13 Source

Anatomy

Measuring about 1.5 m in length and 6.5 cm in diameter, it extends between the ileum and the anus, which are attached to the posterior abdominal wall by the mesocolon (double peritoneal wall). Structurally speaking, it has the following portions: cecum, colon , rectum and anal canal.

Topographically, the large intestine begins in the ileal papilla , in the cecum, which is the primitive appendix. The cecum is intraperitoneal, as is the vermiform appendix. The ascending colon leans against the posterior wall and becomes secondarily retroperitoneal. At the base of the Liver , the colon changes direction in the right colic flexure and becomes a transverse colon, which hangs with a variable length, attached to the posterior abdominal wall by the transverse mesocolon. It changes direction again in the left colic flexure, and goes to the descending colon, which is also attached to the posterior abdominal wall.

Commensal bacteria that synthesize vitamin K and folic acid predominate in the colon , such as:

Escherichia coli
Enterobacter aerogenes
Streptococcus faecalis
Clostridium perfringens

The flora of the large intestine collaborates in the conversion of starch and its derivatives to d-glucose so that it is absorbed, in the process it releases methane CH4 (in gaseous form), which is absorbed according to physiological needs as acid chains fatty .

Large intestine formation

Formed by: the cecum, colon, rectum and anal canal . The large intestine comes embryologically from the part of the primitive intestinal loop that suffers the least number of flexures. When the intestine completes a positive 270 ° turn (counterclockwise) around the axis of the superior mesenteric artery , the beginning of the large intestine is in the right iliac fossa . Taking into account that there is a fixed point (the primitive cloaca that will later originate the anus), the path that the primitive intestine makes draws perfectly the future colic framework of the adult. The colic frame frames the jejunal and ileal handles, which have an inframesocolic situation.

Function

The colon is located immediately after the small intestine. Despite the differences between the digestive systems of the different vertebrates, its main functions are to store waste, extract water, maintain hydration balance and absorb some vitamins .

The large intestine is the last destination of the digestive tract and the terminal phase of digestion . It takes the digested food (chyme) from the small intestine and ends the absorption process. The main function of the colon is to convert the chyme into feces to be excreted. During this process the colon absorbs water from the chyme, changing its state from liquid to solid. Billions of bacteria within the colon synthesize Vitamins K and B, as well as gases hydrogen , [[carbon dioxide]], hydrogen sulfide and methane .

Fiber has a very important function in the large intestine because it helps retain water in it. The water is used to make it softer and more formed stool causing the colon muscles to move the stool to the rectum. As the stool is not defecated, when necessary, the colon continues to absorb water, making it hard and causing constipation. The bacteria present in the large intestine are capable of breaking down some fibers.

Food generally spends more time in the colon than anywhere else in the digestive tract, this time can vary depending on the type of food and each person. It can remain in the colon for approximately 9 hours to several days.

Colon sections

The colon consists of four sections: the ascending colon , the transverse colon , the descending colon , and the sigmoid colon .

Colon Sections (Large Intestine)

Ascending colon

It extends from the cecum to the right colic flexure (colic impression on the underside of the liver, forming the hepatocolic ligament). It is related to the loops of the small intestine, right kidney , and descending portion of the duodenum , in addition to the muscular structures of the posterior wall: psoas , lumbar square , transverse abdomen , femoral nerve , [[lateral femoral cutaneous]], ilio- hypogastric , ilio-inguinal and [[femoral genito]]: gonadal vessels , internal iliac artery and [[iliac bone]] complete the relationships.

Transverse colon

It is the second section and extends through the abdomen from the right side to the left side. Its two ends form two flexures that are called:

Right colic flexure, being the junction of theascending colon with the transverse colon .
Left colic flexure, being the junction of thetransverse colon with the descending colon .

Retained by the transverse mesocolon. Its insertion edge runs along the head and body of the pancreas . Its fusion with the greater omentum determines its anatomical relationships: liver, stomach , descending portion of the duodenum, pancreas, omental pouch, spleen . A peritoneal fold, the phrenololic ligament connects the diaphragm to the left colic flexure.

Descending colon

It is located on the left side between the transverse colon and the sigmoid colon .

It has relationships very similar to those of the ascending colon in terms of the abdominal wall. It progressively leans toward the midline to continue with the sigmoid colon, a kind of “S” that the colon makes before continuing with the rectum at the S3 level. The sigmoid colon has its mesocolon, with the vertex towards the bifurcation of the left common iliac artery. From there it bifurcates into two parts for each of the curves of the sigmoid colon. The sigmoid mesocolon is associated posteriorly with organs of the pelvic cavity, the ureter , the piriformis muscle and the internal iliac artery.

Sigmoid colon

It is the fourth section and is called “sigmoid” because of the S shape. The sigmoid colon joins the rectum , and it empties into the anal canal.

Relationships of the portions of the large intestine

Blind

and ileal papilla: the cecum is the first portion of the large intestine. It is almost always intraperitoneal. In its continuation to the ascending colon it passes from intra to retroperitoneal. For this reason, recesses are formed at the start of the mesoappendix and ileocecal junction. The ileal papilla is at the site where the terminal ileum will empty into the cecum. This opening is made through a longitudinal opening surrounded by circular muscle (the longitudinal one continues directly with the ascending colon and the cecum). Its function is possibly to delay the progress of the intestinal contents towards the large intestine.

Appendix

vermiform: it is a vestigial diverticulum or organ that appears in the large intestine (cecum sector), highly infiltrated by [[lymphoid cells]]. Its length is variable (2-15 cm, on average 9 cm), as well as its position in the abdomen (ventromedial to the cecum, retrocecal, subhepatic, etc.), which largely depends on the amplitude of the mesoappendix. Diagnosis is of great interest because of the frequency with which it becomes inflamed, leading to acute appendicitis and if it spills its contents into the abdominal cavity, it becomes peritonitis .

It has no known digestive functions, although it is a site where immune responses are fulfilled.

Large intestine irrigation

The right part of the large intestine receives branches from the superior mesenteric artery. Starting from the middle of the transverse colon, the left part receives branches from the inferior mesenteric artery :

Left colic artery
Sigmoid arteries
The terminal branch is the superior rectal artery.

The branches of the superior and inferior mesenteric anastomoses in the transverse colon. The veins follow a course analogous to that of the arteries and will converge in the inferior mesenteric vein, which joins the splenic and superior mesenteric vein to form the [[hepatic portal vein]]. They all flow into the portal vein.

Histology of the large intestine

It has no glands , no villi, and no circular folds. It presents, in the serous tunic, evaginations. An evagination filled with fatty tissue constitutes an omental appendix.

In the large intestine there is a large number of goblet exocrinocytes. The epithelial cell populations are the same as in the tenuous intestine. Heteropod multipolar efferent stellate neurons are part of the parasympathetic intraparietal nodes .

Large intestine examination

The large intestine can be explored by:

Opaque enema.

Endoscopy : depending on the depth at which the endoscope is inserted, a rectoscopy, rectosigmoidoscopy or sigmoidoscopy and colonoscopy can be performed, which can be partial if the entire large and total intestine cannot be visualized if it reaches the cecum.

Computed axial tomography

Diseases of the large intestine

Colon cancer
Diverticulitis
Ulcerative colitis
Crohn’s disease
Constipation
Angiodysplasia
Hirschsprung’s disease
Ischemic colitis
Infectious colitis
Gastritis
Appendicitis

Detail of some malformations of the large or medium intestine

Malformations of this portion of the intestine can be:

Abnormalities of the mesentery, such as hernia
Abnormalities of the abdominal wall, where the most common is omphalocele.
Omphalo-mesenteric duct abnormalities, such as the ileal diverticulum.

Rotation defects, such as the left colon (different position from the common one). * atresias , stenosis and duplications that can occur in any of the segments of the intestine and that maintain the patterns already studied.

Some examples of the aforementioned malformations are detailed below: The lumen of the duodenum is obliterated during the second month of development to recanalize later, if this phenomenon does not occur correctly, malformations may appear. In a stenosis of the intestine, the lumen of the caudal portion is narrower than that of the cephalic. If the light is not rechanneled, a total obstruction persists, then an atresia occurs. Of the intestinal malformations, one of the most frequent is omphalocele, produced when the handles do not return to the abdominal cavity. In the hernia they can be found in addition to the intestine, liver and spleen, covered by amnionthis is called gastroschisis. This malformation is frequently accompanied by heart defects and [[chromosomal abnormalities]]; in these cases, it is generally incompatible with life.

Another defect of the abdominal wall is gastroschisis; it is a direct hernia of the intestinal loops in the amniotic cavity ; in which the viscera are not covered by peritoneum or amnion, which can cause damage by being in direct contact with the amniotic fluid