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Colon

The cecum blends seamlessly with the colon    . Upon entering the colon, the food residue first travels up the ascending colon    on the right side of the abdomen. At the inferior surface of the liver, the colon bends to form the right colic flexure    (hepatic flexure) and becomes the transverse colon    . The region defined as hindgut begins with the last third of the transverse colon and continues on. Food residue passing through the transverse colon travels across to the left side of the abdomen, where the colon angles sharply immediately inferior to the spleen, at the left colic flexure    (splenic flexure). From there, food residue passes through the descending colon    , which runs down the left side of the posterior abdominal wall. After entering the pelvis inferiorly, it becomes the s-shaped sigmoid colon    , which extends medially to the midline ( [link] ). The ascending and descending colon, and the rectum (discussed next) are located in the retroperitoneum. The transverse and sigmoid colon are tethered to the posterior abdominal wall by the mesocolon.

Large intestine

This image shows the large intestine; the major parts of the large intestine are labeled.
The large intestine includes the cecum, colon, and rectum.

Homeostatic imbalances

Colorectal cancer

Each year, approximately 140,000 Americans are diagnosed with colorectal cancer, and another 49,000 die from it, making it one of the most deadly malignancies. People with a family history of colorectal cancer are at increased risk. Smoking, excessive alcohol consumption, and a diet high in animal fat and protein also increase the risk. Despite popular opinion to the contrary, studies support the conclusion that dietary fiber and calcium do not reduce the risk of colorectal cancer.

Colorectal cancer may be signaled by constipation or diarrhea, cramping, abdominal pain, and rectal bleeding. Bleeding from the rectum may be either obvious or occult (hidden in feces). Since most colon cancers arise from benign mucosal growths called polyps, cancer prevention is focused on identifying these polyps. The colonoscopy is both diagnostic and therapeutic. Colonoscopy not only allows identification of precancerous polyps, the procedure also enables them to be removed before they become malignant. Screening for fecal occult blood tests and colonoscopy is recommended for those over 50 years of age.

Rectum

Food residue leaving the sigmoid colon enters the rectum    in the pelvis, near the third sacral vertebra. The final 20.3 cm (8 in) of the alimentary canal, the rectum extends anterior to the sacrum and coccyx. Even though rectum is Latin for “straight,” this structure follows the curved contour of the sacrum and has three lateral bends that create a trio of internal transverse folds called the rectal valves . These valves help separate the feces from gas to prevent the simultaneous passage of feces and gas.

Anal canal

Finally, food residue reaches the last part of the large intestine, the anal canal    , which is located in the perineum, completely outside of the abdominopelvic cavity. This 3.8–5 cm (1.5–2 in) long structure opens to the exterior of the body at the anus. The anal canal includes two sphincters. The internal anal sphincter    is made of smooth muscle, and its contractions are involuntary. The external anal sphincter    is made of skeletal muscle, which is under voluntary control. Except when defecating, both usually remain closed.

Questions & Answers

why human body can exit
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Aeryn
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Abdulhakim
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Abdulhakim
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Rofiat Reply
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Wasim
cell is the functional and independent unit
Rofiat Reply
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limilian Reply
cell division of prophase 1 will not take place
limilian
the process by which cell development is form
limilian
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Tsikhulo
Negative & Positive Mechanism
Adepetu
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Adepetu
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Ngwenyi Reply
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Ngwenyi
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Ngwenyi
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frank
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muscles of upper limb
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Luchindo Reply
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Sadiq
Femure
Lemlem
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Jamila
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Obulejo Reply
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Obulejo
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KUSUMA
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KUSUMA
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Sadiq
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Global Reply
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KUSUMA

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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