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Large Intestine

Large Intestine Diagram

This information about the overall structure of the large intestine is part of the section about the digestive system and follows the introduction to the large intestine.

The diagram of the large intestine (below) labels the features of the large intestine.
To understand this topic and the functions of the large intestine it is necessary to know about the structures of the large intestine labelled below and the previous page.

 


Labelled diagram of the Large Intestine

This diagram is interactive - click on a text label (indicated in pink)
for more information about that topic, on another page.

Hepatic Flexure Transverse Colon Transverse Colon Haustrum Appendix Transverse Colon Transverse Colon Appendix Splenic Flexure Haustrum Haustrum Haustra Transverse Colon Haustrum Haustrum Haustrum Transverse Colon Transverse Colon Transverse Colon Epiploic Appendage Transverse Colon Descending Colon Transverse Colon Ascending Colon Epiploic Appendage Transverse Colon Taeniae Coli Descending Colon Sigmoid Colon Epiploic Appendage Taeniae Coli Descending Colon Transverse Colon Ileum Sigmoid Colon Taeniae Coli Sigmoid Colon Ileocaecal Valve Cecum (also called caecum) Cecum (also called caecum) Appendix Appendix Sigmoid Colon Appendix Appendix Sigmoid Colon Sigmoid Colon Sigmoid Colon Rectum Sigmoid Colon Rectum Sigmoid Colon Sigmoid Colon Anus

Short descriptions of the parts of the large intestine labelled in the diagram above follow in the table below.

Short Description

1.

Ileum

At about 4 metres (13 feet) in length, the ileum is the final section of the small intestine. It follows the duodenum and jejunum and is separated from the cecum by the ileocecal valve. The functions of the ileum include absorbing vitamin B12, bile salts and any products of digestion that were not absorbed by the jejunum. Undigested food, waste and water pass onwards from the ileum to the colon part of the large intestine by the action of peristalsis.

2.

Ileocecal sphincter (valve)

The ileocecal valve (also known as the ileocaecal valve) is located at the junction of the ileum of the small intestine and the colon of the large intestine. The ileocecal valve restricts the reflux of the contents of the colon back into the ileum.

3.

Caecum (= cecum)

The caecum (also called the cecum) is a pouch that connects the ileum with the ascending colon of the large intestine.

4.

Appendix

The appendix (also known as the vermiform appendix) is a blind-ended tube connected to the caecum. In humans the appendix is a vestigial structure, meaning that it is said to have has lost most or all of its original function through the process of evolution, and so is now only a shrunken evolutionary remainder of a structure that had an important function in an ancestor of humans.
It may have contained bacteria that aided digestion of cellulose molecules in plants. (Modern humans are not able to digesting more than a very small amount of cellulose per day.)

5.

Mesentery

The mesentery labelled on the diagram above is not really part of the large intestine but is attached to the ileum (included in the diagram because it is the route by which material enters the large intestine from the small intestine).

The mesentery connects the jejunum and ileum (parts of the small intestine) to the back wall of the abdomen. It consists of two layers of peritoneum between which are blood vessels, lymph vessels, and nerves.

6.

Colon

The colon is the last major part of the human digestive system. It consists of four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon (the term "proximal colon" generally refers to the ascending colon and the transverse colon).

7.

Ascending Colon

The ascending colon is the first of the four main sections of the colon. It ascends (i.e. "goes upwards") on the right side of the abdomen as far as the hepatic flexure which is located at the underside of the liver where the colon makes a left turn into the transverse (section of) the colon.

8.

Transverse Colon

The transverse colon is the second of the four main sections of the colon. It traverses (i.e. "goes across") from the hepatic flexure on the right-side of the abdomen to the splenic flexure on the left-side of the abdomen where the colon turns downwards into the descending (section of) the colon.

9.

Descending Colon

The descending colon is the third of the four main sections of the colon. It descends (i.e. "goes downwards") on the left side of the abdomen from the splenic flexure located beneath the lower border of the spleen, as far as the sigmoid (section of) the colon.

10.

Sigmoid Colon

The sigmoid colon is the fourth of the four main sections of the colon. It begins near the iliac crest of the left hip/pelvic bone and forms a loop that terminates in the rectum.

11.

Rectum

The human rectum is often defined as the last 6 to 8 inches (approx 15 cm) of the adult large intestine. However, that definition does not include (as part of the large intestine) the anal canal to which the rectum is attached. The function of the rectum is to store solid indigestible material and gases until its contents leaves the body via the anal canal and then the anus.

12.

Anal Canal

The anal canal is the terminal part of the large intestine. It is located between the rectum and the anus - some texts say "extending from the anorectal junction to the anus".
The anal canal has three parts, the zona columnaris (upper half of the anal canal, above the pectinate line) and the zona hemorrhagica and zona cutanea below the pectinate line and separated by Hilton's white line. It is directed downwards and backwards.

13.

Anus

The anus is the external opening of the rectum. Its opening / closure is controlled by sphincter muscles. The function of the anus is the expulsion from the body of faeces, the process of which is called defecation.

14.

Right colic flexure (hepatic flexure)

The right colic flexure is the sharp bend between the ascending colon and the transverse colon.
It is also known as the hepatic flexure because it is located next to the liver.

15.

Left colic flexure (splenic flexure)

The left colic flexure is a sharp bend between the transverse colon and the descending colon.
It is also known as the splenic flexure because it is located near to the spleen.

16.

Taeniae coli

The taenia coli (also known as the teniae coli, terms derived from the Latin for "flat band") is a band of longitudinal smooth muscle that passes along the outside of each of the four sections of the colon - i.e. the ascending, transverse, descending and sigmoid colons.
It consists of three separate longitudinal ribbons of smooth muscle called:

  • the mesocolic coli, or mesocolic taenia
  • the free coli or free taenia, and
  • the omental coli or omental taenia

These three ribbons or "bands" of smooth muscle are visible on the outer-surface of the large intestine and shown in the diagram above, together with some appendices epiploicae.
The teniae coli contracts lengthwise to produce haustra, which are the bulges in the sections of colon that form the large intestine.

17.

Epiploic appendages
(= epiploicae appendices)

When looking at the outer surface of the large intestine some appendages are seen attached to the taenia coli. These are called epiploicae appendages or epiploicae appendices (in the plural, the singular terms* being epiploic appendage or epiploic appendix). These are sacs of omentum distended with fat.
*Different textbooks use slightly different words so it is useful to know and recognize both versions.

18.

Haustra

The 4 main parts of the colon (ascending colon, transverse colon, descending colon and sigmoid colon) are drawn as sections that appear to consist of a series of bulges - see diagram above. These rounded "bulges" are called haustra (plural) and are formed due to contractions of the taeniae coli gathering the main structure of the 4 sections of the colon into a series of pouches.

19.

Haustrum

Descriptions of the anatomy of the large intestine generally mention the haustra (as above, a plural term). It is useful to also know the singular word, which is haustrum.

See also the stomach, the liver, the small intestine and an introduction to the large intestine.

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