Colon: Definition, Anatomy, Structure, Characteristics, Function, Associated Diseases and Recommendations

The human body has two types of intestines.

The first one that is connected to the stomach, called the small intestine and operates the middle part in the process of digestion of food. And the final part of the digestion process, called the large intestine. It is a large tube that escorts waste from the body .

The colon is an inverted, U-shaped part. By definition, the colon is part of the large intestine and extends between the cecum.

The colon can be easily recognized through several different morphological features, such as semilunar folds and bags called haustra.

Histologically, the mucosa is lined by a simple columnar epithelium and contains crypts of Lieberkuhn and numerous goblet cells.

Anatomy

Parts of the colon

The colon is the longest part of the large intestine. It starts from the cecum at the ileocecal valve and ends at the rectum.

The colon frames the convolute of the small intestine in the abdominal cavity.

However, it can be shortened and quite flexible in the event of incomplete rotation of the umbilical loop during embryogenesis.

The colon can be subdivided into four parts: ascending, transverse, descending, and sigmoid colon.

The ascending colon lies secondary retroperitoneally on the right side of the abdominal cavity and moves to the right colic flexure on the lower side of the liver.

From there, the transverse colon moves intraperitoneally to the spleen, forming the left colic angle.

This part is attached to the posterior abdominal wall by the mesocolon and is therefore very flexible.

Beginning at the left colic flexure, the descending colon proceeds retroperitoneally down the left abdominal wall and changes to the S-shaped sigmoid colon in the left iliac fossa.

Because the sigmoid colon lies intraperitoneally, it also has a mesocolon.

This last part of the colon ends in the rectum at S2 and S3.

Structure of the colon

The colon is made up of several layers, from the inside to the outside:

  • A mucosa without a valve.
  • A highly vascularized and innervated submucosa.
  • Circular (internal) and longitudinal (external) smooth muscle.
  • A serous envelope (peritoneum).

Morphological characteristics

Macroscopically, the colon has some different morphological characteristics compared to the small intestine.

The semilunar folds arise on the inner surface through muscular contractions. These are simply functionally caused and therefore movable. These folds form pockets on the outer surface (haustra).

Macroscopically, the colon has some different morphological characteristics compared to the small intestine.

The longitudinal musculature is concentrated in three strong ribbon-like strips (taeniae coli).

The mesocolon joins the mesocolic tapeworm and the greater omentum to the omental tapeworm, while the free (or liberal) tapeworm is free and fully visible.

Another characteristic of the colon is the small fat-filled sacculation formed by the serosa (appendages epiploicae).

Blood supply

Branches of the superior mesenteric artery (right colic artery, middle colic artery, and colic branch of the ileocolic artery) supply the ascending and transverse colon.

The descending colon and the sigmoid colon are supplied by branches of the inferior mesenteric artery (left colic artery and sigmoid arteries).

The left and middle colic arteries form Riolan’s (inconstant) anastomosis.

Venous blood drains through the veins corresponding to the superior and inferior mesenteric veins.

Innervation

Up to the Cannon-Boehm point in the left colic angle, the sympathetic innervation is carried by the nerves of the superior mesenteric plexus, while the parasympathetic innervation is carried by the vagus nerve (cranial nerve X).

After that point, the inferior mesenteric plexus nerves carry the sympathetic innervation and the pelvic splanchnic nerves carry the parasympathetic innervation.

Histology

The colon has the typical histological structure of the digestive tract: mucosa, submucosa, muscularis and serous, adventitial.

The mucosa is lined by a simple columnar epithelium (epithelial lamina) with long microvilli.

It is covered by a layer of mucus that helps transport stool.

The mucosa does not contain villi but rather many crypts of Lieberkuhn in which numerous goblet cells and enteroendocrine cells are found.

The connective tissue layer (mucosa of the lamina propria) is filled with macrophages, plasma cells, and other immune cells.

The submucosa comprises blood vessels, lymph nodes, and particularly fatty tissue.

The internal circular musculature of the muscularis is strongly pronounced, while the external longitudinal musculature is found practically only in tapeworms.

Function

The main task of the colon is the temporary storage and transport of stool.

The function of the colon is to eliminate the remains of food from which the nutrients have already been extracted, it also eliminates bacteria and other wastes from the body’s metabolism.

This process is called intestinal peristalsis and lasts approximately 36 hours.

In this way, it absorbs about 1 liter of water daily, which leads to thickening of the stool.

In addition, it absorbs sodium, potassium, and chloride, but it can also secrete potassium.

The intestinal physiological flora is rich in anaerobic bacteria (approximately 1011 per gram) that live in symbiosis with the human body.

They fulfill other essential functions such as the breakdown of indigestible food ingredients (eg cellulose), the production of vitamin K, and the support of the immune system.

Also called the large intestine, the colon follows the small intestine and forms the last part of the digestive system. It consists of several parts:

  • The cecum (from which the vermiform appendix emerges).
  • The ascending colon (right).
  • The transverse colon.
  • The descending colon (left).
  • The sigmoid colon.
  • The rectum.

Its function is mainly to eliminate waste, absorb water, maintain water balance and absorb certain vitamins.

The chyle from the small intestine lacks almost all (90%) of the nutrient already absorbed by the digestive system.

Chyle mixes in the colon with mucus and intestinal bacteria to form fecal material.

The bacteria capable of digesting the fibers form new molecules that the colon can assimilate.

The pH is between 4.5 and 7.5. The first thing that is eliminated, as they pass through the colon, are liquids and salt.

The waste then reaches the sigmoid, where it is stored.

Later, when the body is ready to defecate, the waste is expelled through the rectum.

Size

The colon is wider than the small intestine, but it is also shorter.

The small intestine is approximately 6.7 meters long, and 4 to 8 centimeters in diameter.

Colon diseases

The colon, also known as the large intestine, is part of the digestive system.

It is a long, hollow tube at the end of your digestive tract where the body makes and stores stool.

Many disorders affect the colon’s ability to function properly.

Diseases that are generally associated with the colon are:

Colorectal cancer

This type of cancer starts in the colon or near the rectum (lower colon).

One of the most common causes of death associated with cancer.

Colonic polyps

They represent an abnormal growth of tissue located in the inner lining of the colon or rectum.

Polyps are benign and non-cancerous growths. However, they can sometimes become cancerous.

Polyps can be: adenomatous which can turn into cancer.

And hyperplastic and inflammatory polyps.

Colon dysplasia

Dysplasia are cells located in the lining of the colon that look abnormal under a microscope.

These cells are generally not cancerous, but they can turn into cancer cells over time.

Colon dysplasia can develop in people who have had illnesses such as ulcerative colitis or Crohn’s disease for many years .

The spastic colon

This condition is also known as irritable bowel, it is more than a colon problem.

They are spontaneous contractions or loss of movement in the muscles of the small and large intestines.

Ulcerative colitis

They are ulcers that appear in the colon and rectum.

Diverticulitis

Diverticulitis is an inflammation or infection that occurs in the bags of the colon.

Prevention

To promote good colon health, you should eat a healthy diet high in fruits and vegetables, rich in fiber, drink adequate amounts of water, and exercise regularly.

Supplements, such as curcumin and omega-3s, can help reduce inflammation.

It may also be helpful to take vitamins such as: vitamin B6.

Colon cleansing

It is common for people to use colon cleansing substances to maintain a healthy colon.

This process includes the administration of laxatives, tea, supplements, enemas, or colon hydrotherapy to remove waste from the colon.

It can have side effects when cleaning is done, and some of these methods can even be dangerous.

Treatment of diseases that occur in the colon will vary depending on the disease and its severity.

Treatment generally includes a healthy diet, medications, and in some more serious cases, surgery.