The Anatomy of the Ascending Colon

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The colon is part of the large intestine, and it has several different sections: ascending, transverse, descending, and sigmoid. The ascending colon is the first section. It is located in the digestive tract between the end of the small intestine and the second part of the colon, the transverse colon. It is also sometimes called the right colon.

In this article, learn more about the anatomy and function of the ascending colon, as well as conditions that can affect it and tests that may be done.

A physician wearing a pink stethoscope and a white coat holding a 3D representation of a colon that demonstrates different diseases and conditions that can occur in that organ.

Peter Dazeley / Getty Images

Anatomy

The colon is part of the digestive tract, where food is broken down into substances that the body can use. The ascending colon is the first section of the colon. It receives partially digested food from the small intestine.

Structure

The ascending colon is about 8 inches (20-25 centimeters) long and 2.5 inches in diameter. The inside of the ascending colon is lined with smooth muscles that contract and move stool along its length.

It’s held in place by the tissues and membranes that line the abdominal wall. There are pouches inside the length of the colon, which increases the surface area on the inside, allowing for more absorption.

The innermost layer of the ascending colon is called the mucosa. It has goblet cells, which help create the mucus needed to help waste move along the length of the colon.

The next layers are the sub-mucosa, which contains nerves and blood vessels, and the muscularis, which contains smooth muscle. The outermost layer is the serosa, which secretes a fluid to reduce friction from smooth muscle contraction.

Location

The ascending colon is located on the right side of the abdomen. It receives the digesting food from the small intestine. At its start, it is connected to the cecum, which is the first part of the large intestine.

At its end, the ascending colon makes a left turn where it meets the second part of the colon, the transverse colon. The transverse colon goes from right to left across the abdomen.

Anatomical Variations

Variations and birth defects in the ascending colon are not common. Malrotations of the colon, where the intestine becomes twisted, are usually discovered in newborns because they often cause digestive symptoms. Surgery is used to correct the problem.

The way blood is supplied to the parts of the colon has some variations in the branching of the arteries. The artery that supplies the right colon is the superior mesenteric artery. There have been rare case reports of the blood supply instead coming from the inferior mesenteric artery.

Function

The colon is a hollow tube, and waste material (stool) passes through it on its way out of the body through the anus. The purpose of the colon is to absorb water and electrolytes from the stool. Most vitamins and minerals are absorbed in the small intestine.

When the waste passes from the small intestine and into the cecum, it is mixed with various types of bacteria. This bacteria further breaks down the waste and helps the absorption of a few more vitamins, such as vitamins K, B1, B2, and B12.

Water is absorbed from the waste material as it passes through the colon, turning it from mostly liquid into solid stool.

Associated Conditions

There are several diseases and conditions that can affect the ascending colon. The other parts of the colon might be affected by these conditions as well.

Colon Cancer

Colon cancer can begin in the ascending colon. It is often not found until the cancer is advanced because it may not cause any symptoms.

When stool passes through the ascending colon, it has just come from the small intestine, and it is mostly liquid. It can therefore bypass a growing tumor that is partially blocking the colon. These tumors may be treated with surgery to remove part of the colon, and with chemotherapy and/or radiation.

Colon Polyps

Colon polyps are stalk-like growths that occur on the inner intestinal wall. They protrude into the interior of the colon. If they become large, they can block waste material from passing through.

Polyps are the precursor to cancer. During a screening colonoscopy, any polyps that are found will be removed so that they do not continue to grow and present a risk of cancer.

Diverticular Disease

Diverticular disease is a condition in which outpouchings develop in weakened sections of the lining of the colon. It’s common for people over the age of 40 to have these pouches in the colon lining, and most people over the age of 50 have them.

They may not cause any symptoms unless they become infected, which is called diverticulitis. Diverticulitis may cause fever, nausea, abdominal pain, and diarrhea. Diverticulitis is most often treated with antibiotics, but severe cases may need surgery.

Inflammatory Bowel Disease

Crohn’s disease, ulcerative colitis, and indeterminate colitis are forms of inflammatory bowel disease (IBD) that can affect the ascending colon. IBD causes inflammation and ulcers in the digestive tract. This can lead to signs and symptoms in the digestive tract, such as intestinal bleeding, abdominal pain, and diarrhea.

Further, IBD can cause extra-intestinal complications that include fatigue, skin conditions, eye problems, and various forms of arthritis.

Tests

Tests that are used to assess the health of the entire colon will include assessment of the ascending colon.

Colonoscopy

Colonoscopy is a test where a thin, flexible tube with a light is inserted into the rectum and moved up through the length of the colon. This test is done under anesthesia. The preparation for this test includes cleaning the colon of any stool, which is done using strong laxatives and fasting.

Computed Tomography

Computed tomography (CT) is used to look at the organs in the abdomen. It is a type of X-ray that can create an image of the colon and other body structures. This test can show, for instance, if there are any tumors in the colon.

To prepare for this test, it’s often necessary to fast for several hours prior. Contrast solution may be given, either by mouth or through an IV, during this test. The contrast helps certain tissues show up better on the CT scan images.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) uses a magnetic field to see the structures and organs inside the body. It may be done with or without contrast. Contrast may be given in the form of a drink or administered through an IV (or both may be used in the same patient). No radiation is used in this test.

Positron Emission Tomography

Positron emission tomography (PET) is used to find tumors. Sugar treated with a low level of radiation is given through an IV before the test. If any tumor cells are present, they will take up this sugar and show up on films taken during the test.

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