Location and appearance of two example colorectal tumors
Scheme of digestive tract, with rectum marked
Longitudinally opened freshly resected colon segment showing a cancer and four polyps. Plus a schematic diagram indicating a likely field defect (a region of tissue that precedes and predisposes to the development of cancer) in this colon segment. The diagram indicates sub-clones and sub-sub-clones that were precursors to the tumors.
The inside of a normal human rectum in a 70-year-old, seen during colonoscopy
Colon cancer with extensive metastases to the liver
Retroflexed view of the human rectum seen at colonoscopy showing anal verge
Relative incidence of various histopathological types of colorectal cancer. The vast majority of colorectal cancers are adenocarcinomas.
A digital rectal exam is conducted to investigate or diagnose conditions including of the prostate.
Micrograph of colorectal adenocarcinoma, showing "dirty necrosis".
Arteries of the pelvis
A diagram of a local resection of early stage colon cancer
Blood vessels of the rectum and anus
A diagram of local surgery for rectal cancer
Cross-section microscopic shot of the rectal wall
Colon and rectum cancer deaths per million persons in 2012
Dog rectum cross-section (40×)
Microscopic cross-section of the rectum of a dog (400×), showing a high concentration of goblet cells in amongst the column-shaped lining. Goblet cells can be seen as the circular cells with a clear inner material (cytoplasm).

Sigmoidoscopy (from the Greek term for letter "s/ς" + "eidos" + "scopy": namely, to look inside an "s"/"ς"-like object) is the minimally invasive medical examination of the large intestine from the rectum through to the nearest part of the colon, the sigmoid colon.

- Sigmoidoscopy

Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine).

- Colorectal cancer

Colorectal cancer may be diagnosed by obtaining a sample of the colon during a sigmoidoscopy or colonoscopy.

- Colorectal cancer

However, although in absolute terms only a relatively small section of the large intestine can be examined using sigmoidoscopy, the sites which can be observed represent areas which are most frequently affected by diseases such as colorectal cancer, for example the rectum.

- Sigmoidoscopy

Colonoscopy and sigmoidoscopy are forms of endoscopy that use a guided camera to directly view the rectum.

- Rectum

Rectal cancer, a subgroup of colorectal cancer specific to the rectum.

- Rectum

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Overall

Front of abdomen, showing the large intestine, with the stomach and small intestine in gray.

Large intestine

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Last part of the gastrointestinal tract and of the digestive system in vertebrates.

Last part of the gastrointestinal tract and of the digestive system in vertebrates.

Front of abdomen, showing the large intestine, with the stomach and small intestine in gray.
Illustration of the large intestine.
Inner diameters of colon sections
Colonic crypts (intestinal glands) within four tissue sections. The cells have been stained to show a brown-orange color if the cells produce the mitochondrial protein cytochrome c oxidase subunit I (CCOI), and the nuclei of the cells (located at the outer edges of the cells lining the walls of the crypts) are stained blue-gray with haematoxylin. Panels A, B were cut across the long axes of the crypts and panels C, D were cut parallel to the long axes of the crypts. In panel A the bar shows 100 µm and allows an estimate of the frequency of crypts in the colonic epithelium. Panel B includes three crypts in cross-section, each with one segment deficient for CCOI expression and at least one crypt, on the right side, undergoing fission into two crypts. Panel C shows, on the left side, a crypt fissioning into two crypts. Panel D shows typical small clusters of two and three CCOI deficient crypts (the bar shows 50 µm). The images were made from original photomicrographs, but panels A, B and D were also included in an article and illustrations were published with Creative Commons Attribution-Noncommercial License allowing re-use.
Histological section.
Colonoscopy image, splenic flexure,
normal mucosa. You can see spleen through it : the black part
Micrograph of normal large instestinal crypts.
Anatomy of normal large intestinal crypts
Intestines
Colon. Deep dissection. Anterior view.

Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation.

Sigmoidoscopy is a common diagnostic technique used to examine the sigmoid colon.

Bacteroides are implicated in the initiation of colitis and colon cancer.

Diagram of stomach, intestines and rectum in the average human

Gastrointestinal tract

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Tract or passageway of the digestive system that leads from the mouth to the anus.

Tract or passageway of the digestive system that leads from the mouth to the anus.

Diagram of stomach, intestines and rectum in the average human
Illustration of the small intestine

In humans, the small intestine is further subdivided into the duodenum, jejunum, and ileum while the large intestine is subdivided into the cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.

Gastrointestinal cancer may occur at any point in the gastrointestinal tract, and includes mouth cancer, tongue cancer, oesophageal cancer, stomach cancer, and colorectal cancer.

Parts of the tract may be visualised by camera. This is known as endoscopy if examining the upper gastrointestinal tract and colonoscopy or sigmoidoscopy if examining the lower gastrointestinal tract. Capsule endoscopy is where a capsule containing a camera is swallowed in order to examine the tract. Biopsies may also be taken when examined.

Colonoscopy being performed

Colonoscopy

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Endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus.

Endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus.

Colonoscopy being performed
A container of PEG (polyethylene glycol or macrogol) with electrolyte used to clean out the intestines before certain bowel exam procedures such as a colonoscopy.
Schematic overview of colonoscopy procedure
Polyp is identified.
A sterile solution is injected under the polyp to lift it away from deeper tissues.
A portion of the polyp is now removed.
The polyp is fully removed.

It can provide a visual diagnosis (e.g., ulceration, polyps) and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions.

Colonoscopy is similar to sigmoidoscopy—the difference being related to which parts of the colon each can examine.

The endoscope is then passed through the anus up the rectum, the colon (sigmoid, descending, transverse and ascending colon, the cecum), and ultimately the terminal ileum.