In the

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

of humans and homologous primates, the descending colon is the part of the colon extending from the left colic flexure to the level of the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poste ...

(whereupon it transitions into the

sigmoid colon The sigmoid colon (or pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus ''s ...

). The function of the descending colon in the digestive system is to store the remains of digested food that will be emptied into the

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...

. The descending colon is on the left side of the body (barring any malformations). The term left colon is hypernymous to ''descending colon'' in precise use; many casual mentions of the left colon chiefly concern the descending colon.

Structure

The descending colon extends from the left colic flexure at the upper left part of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the tors ...

inferior-ward through the left hypochondrium and lumbar regions, along the outer border of the left

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

, ending at the level of the

at the lower left part of the abdomen, being contunued thenceforth as the

. It usually

retroperitoneal The retroperitoneal space (retroperitoneum) is the anatomical space (sometimes a potential space) behind (''retro'') the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum on thei ...

(being lined by peritoneum on its anterior and lateral aspects), but may be suspended (usually short)

mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines ...

in a minority of individuals. The arterial supply comes via the left colic artery.

Function

While the first part of the large intestine is responsible for the absorption of water and other substances from the chyme, the main function of the descending colon is to store waste until it can be removed from the body in solid form, when a person has a bowel movement. The stools gradually solidify as they move along into the descending colon.The Function Of The Colon
Retrieved on 2010-01-21

Clinical significance

There are several diseases associated with the descending colon. Among the most common are the

inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, Crohn's disease and ulcerative colitis being the principal types. Crohn's disease affects the small intestine and large intestine, as wel ...

s (such as

ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood ( hematochezia). Weight loss, fever, an ...

or Crohn’s disease) and

colon cancer 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). Signs and symptoms may include blood in the stool, a change in bowel ...

Ulcerative colitis

Ulcerative colitis can affect any part of the colon (and other

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

, such as the mouth), but when it affects the descending colon, it is called ''left-sided colitis''.

Inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

and

ulcers An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...

on the lining of the intestine mark its presence. Symptoms of ulcerative colitis include

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin ...

, bleeding, fever, abdominal pain, too much mucus in fecal material, and appetite and weight loss. Treatment methods can vary widely, ranging from changes in diet to drug therapy to corrective surgery, depending on the severity of the condition and the overall health of the patient.

Crohn’s disease

When a person has Crohn’s disease or Crohn’s colitis, they have lesions on the tissues of the intestine; this makes it hard for the intestine to absorb water and salt. The symptoms which may develop from this disease include abdominal pain, diarrhea or

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel moveme ...

, nausea and vomiting, fever, blood in the stool, weight loss, abscesses and fatigue. There is no cure for Crohn’s disease although many treatments are available. Symptomatic treatment with antidiarrhoeals is common in low level cases where the inflammation is reasonably under control. Steroid and/or sulphasalazine treatment are usually the first line of drug based management, although newer drugs along the

TNF inhibitor A TNF inhibitor is a pharmaceutical drug that suppresses the physiologic response to tumor necrosis factor (TNF), which is part of the inflammatory response. TNF is involved in autoimmune and immune-mediated disorders such as rheumatoid arthritis ...

line (such as

infliximab Infliximab, a chimeric monoclonal antibody, sold under the brand name Remicade among others, is a medication used to treat a number of autoimmune diseases. This includes Crohn's disease, ulcerative colitis, rheumatoid arthritis, ankylosing spo ...

and

adalimumab Adalimumab, sold under the brand name Humira, among others, is a monoclonal antibody used to treat rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, Crohn's disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurat ...

) are becoming more widespread in the treatment of inflammatory colonic conditions. Diet and lifestyle changes can also be useful, as stress may exacerbate inflammatory processes.

Colon cancer

Cancer of the descending colon is a serious disease. A person can have colon cancer yet have no symptoms in the early stages. As such, regular colorectal examinations or fecal occult blood testing are necessary for catching the disease in its early stages. However, there are some signs that can indicate colon cancer; they include abrupt changes in bowel habits, bleeding from the rectum, black stools, frequent constipation, and mucus in the stools. Treatment options depend on the stage of the cancer and the overall health of the patient.

References

External links

Lotti M. Anatomy in relation to left colectomy
* - "The large intestine." * {{Authority control Large intestine