The colon is the longest part of the large bowel or large intestine, measuring around 60 inch (around 1.5 meters). The large bowel is a tube-like organ that begins from the small intestine and ends at the anus. The colon extends from a pouch-like structure called the cecum and ends at the rectum (the part of the large bowel where stools are stored). The rectum is the lowest part of the large bowel and measures around 8 inch in length.
The colon is divided into four main parts.
- Ascending colon: This is the first part of the colon. It begins from the cecum, which acts as the connecting link between the colon and the last part of the small bowel (ileum). When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure) and marks the start of the transverse colon.
- Transverse colon: It begins at the right colic flexure (the site where the ascending colon takes a sharp 90-degree turn) and moves horizontally (transversely). At the level of the spleen, the transverse colon takes a 90-degree turn and continues as the descending colon.
- Descending colon: It begins at the left colic flexure (the site where the transverse colon takes a 90-degree turn) and moves downward (descends) toward the pelvis.
- Sigmoid colon: It is an “S” shaped structure measuring around 15.7 inch. It is the last part of the colon and begins when the descending colon moves toward the midline (medially). It is the narrowest part of the colon.
To check the health of the colon, the doctor may perform a colonoscopy. It is a medical procedure to examine the inside of the colon. A colonoscopy is done with the help of an instrument called a colonoscope. It is a long, thin and flexible tube-like instrument that carries a camera and a light source at one end.
Colonoscopy is generally performed on an outpatient basis (you don’t need to get admitted or stay overnight in the hospital for the procedure), though your doctor may keep you under observation for a few hours after the procedure. It helps to diagnose various bowel (gastrointestinal) conditions presenting as bleeding, abdominal pain or changes in bowel habits. A piece of tissue (biopsy) can also be removed using the colonoscope for diagnostic purposes. Removal of colorectal polyps (small clumps of tissue formed in the inner lining of the large bowel) can also be done with the help of colonoscopy. The removal of polyps is essential because they may later turn into colon cancer.
Colonoscopy may be done at the doctor’s office or in the outpatient department of a medical center or hospital.
Before the procedure
Your doctor may
- Order some blood tests and imaging studies (such as X-ray, computed tomography or CT scan and magnetic resonance imaging or MRI).
- Ask you of any chronic health conditions.
- Ask you about any medications you are on.
- Ask about any allergies you may have.
- Explain the procedure in detail, including possible complications and address your queries and concerns related to it.
- Obtain your written consent.
- Explain to you the steps for bowel cleansing (bowel preparation). The steps for bowel preparation include
- Using enemas
- Not eating solid foods for one to three days before the test
- Taking laxatives
- Ask you to drink plenty of clear liquids for one to three days before the test. Clear fluids include water, clear coffee or tea, gelatin, fat-free bouillon or broth, sports drinks without added color and strained fruit juices.
During the test
- You will be asked to wear a hospital gown.
- An intravenous (IV) line will be attached, and a sedative will be administered. This will make you comfortable and pain-free during the procedure.
- You will lie on your left side with your knees drawn up toward your chest.
- The doctor will gently insert the colonoscope through the anus. The colonoscope will be slowly advanced up to the lowest part of the small bowel.
- Air is inserted through the colonoscope for a better view of the inside.
- Suction may be done for removing fluid or stool.
- The scope will be slowly moved out as the doctor examines the inside of the bowel while withdrawing it.
- Your doctor may remove small tissue samples (biopsy) or polyps using tiny tools inserted through the colonoscope.
- Therapeutic procedures, such as laser therapy, may be done if needed during the procedure.
- Photographs of the inside of the bowel may be taken by the camera at the end of the colonoscope.
After the procedure
You will be able to go home about an hour after the test. You will need someone’s help to take you home due to the effect of sedatives.
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Mayo Clinic. Colonoscopy. https://www.mayoclinic.org/tests-procedures/colonoscopy/about/pac-20393569