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The large intestine is the made up of the cecum, colon, rectum and anal canal.

In this lesson, you will learn about the anatomical features and basic functions of these large intestine segments.

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Large Intestine

By the time food passes through the small intestine, digestion is complete and most of the nutrient absorption has occurred. Now food is ready for its final stage of the digestive process as it passes through the large intestine. In this lesson, you will learn about the anatomy and basic functions of the large intestine.

The large intestine surrounds the outer edge of the small intestine.

Image Large Intestine

The large intestine is the portion of the intestine that extends from the ileocecal valve to the anus. We previously learned that the ileocecal valve is the valve between the small intestine and the large intestine that prevents material from flowing back into the small intestine. We see from the picture of the large intestine that it is, in fact, larger than the small intestine – hence its name. However, the large intestine is quite a bit shorter than its counterpart, measuring approximately five feet or one and a half meters in length.We also see from the picture that the large intestine looks somewhat like a frame as it surrounds the small intestine.

As we follow the path of the large intestine, the different sections change names. However, their basic function remains the same, and that is to absorb water and a few other products from the undigested food mass and carry the remaining useless waste material out of the body.

Cecum and Appendix

The cecum is continuous with the small intestine.
cecum and ileum diagram

The first part of the large intestine is called the cecum. The cecum is defined as a large pouch forming the beginning of the large intestine.

From the picture, we notice that it looks somewhat like a pouch and that it is continuous with the last part of the small intestine, called the ileum. We also see that food passes from the ileum to the cecum through the ileocecal valve.This is also the location for the appendix, which is a blind-ended tube connected to the cecum.

The appendix is sometimes referred to as the vermiform appendix, and although that name sounds more complicated, it might help you remember the organ, because the term ‘vermiform’ comes from the Latin language and means ‘worm-shaped.’ As you can see, the appendix hangs from the cecum and does look somewhat like a worm.Unfortunately, the long, slender shape of the appendix makes it a potential trouble spot because it can easily become twisted.

This makes it a common site for bacteria to gather and multiply, leading to inflammation. You may have heard of someone who suffered an inflammation of the appendix, known as an appendicitis. An appendicitis is a medical emergency and typically requires surgical removal of the structure. If treatment is not received, an inflamed appendix could burst, spilling infectious material into your abdominal cavity. The function of the appendix is controversial. While many think that the appendix serves no purpose, others theorize that it may play a role in the immune system.

Colon

The colon is the part of the large intestine that extends from the cecum to the rectum. The colon does not play a major role in nutrient absorption. However, it does function to absorb water, salts, and some fat-soluble vitamins. The colon is divided into four sections, and we see from the picture that every time the colon takes a turn, we assign a new name.

The colon absorbs water, salt and vitamins.
Colon Function

The ascending colon passes upward in the abdomen, and you can recall this term by remembering that the word ‘ascending’ means ‘upward.

‘ At the top of the ascending colon, we see that the colon takes an abrupt turn. This marks the beginning of the transverse colon. This term can be easily recalled if you remember that the term ‘transverse’ means ‘lying across.’ We see from the picture that the transverse colon lies across the abdomen.At the end of the transverse colon, we again see an abrupt turn downward, and this marks the beginning of the descending colon. As with the other terms, we see that the name describes the section because the term ‘descending’ means ‘moving down.’ At the base of the descending colon, we see a turn inward that creates a final section of the colon called the sigmoid colon.

This section is somewhat different because it’s S-shaped. However, the difference can help you recall the name because the ‘sigmoid’ colon is ‘S-shaped.’ In fact, the word ‘sigma‘ is Greek for S-shaped.

Haustra

The colon is the main section of the large intestine, and if we take a look inside, we see that the colon lacks the villi, or small projections, that helped increase nutrient absorption in the small intestine.

This is likely because most nutrient absorption has been completed before it reaches the large intestine.

The inside of the colon lacks villi.
cross section lacking villi

We also see an anatomical feature that we have not previously encountered called haustra. Haustra are pouches in the wall of the colon. Haustra are caused by longitudinal bands that run along the intestinal wall.

Because these longitudinal bands are shorter than the intestine, they create the puckered appearance of the colon.

Rectum and Anal Canal

After passing through the sigmoid colon, the waste material that is left has lost most of its water content and is passed into the rectum. The rectum is a temporary storage site for digestive wastes. It is a short section measuring about four and a half inches, or 12 centimeters, in length.

The presence of waste material in the rectum causes an increase in pressure and the urge to go to the bathroom.If this is to occur, the waste material descends into the final section of the digestive tract, known as the anal canal. The anal canal is the terminal part of the large intestine.

This section of the large intestine is only about two to four centimeters in length and is the final stop for waste before exiting the body. It is surrounded by sphincters that give you some control over when you choose to go to the bathroom.

The anal canal is the last stop in the digestive process.
Anal Canal

Lesson Summary

Let’s review.

The large intestine is the portion of the intestine that extends from the ileocecal valve to the anus. The basic function of the large intestine is to absorb water and a few other products from the undigested food mass and carry the remaining useless waste material out of the body.The cecum is a large pouch forming the beginning of the large intestine.

Hanging from the cecum is a blind-ended tube called the appendix. This structure is long and worm-like in appearance and can be the site for bacteria to accumulate and grow. If this happens, it leads to an appendicitis, which is an inflammation of the appendix.The colon is the part of the large intestine that extends from the cecum to the rectum. The colon is divided into four sections.

The ascending colon passes upward in the abdomen. The transverse colon lies across the abdomen. The descending colon travels downward in the abdomen and is followed by the sigmoid colon, which curves inward and follows an S-shaped path. The outer wall of the large intestine has a notable puckered appearance.

These pouches in the wall of the colon are called haustra.After passing through the colon, the remaining waste material is passed into the rectum. The rectum is a temporary storage site for digestive wastes. When you are ready to go to the bathroom, the waste material descends into the terminal part of the large intestine, known as the anal canal. This is the final stop for waste before exiting the body.

Learning Outcomes

After this lesson, you will be able to:

  • Describe the overall structure, parts and function of the large intestine
  • Identify the appendix and explain what causes an appendicitis
  • List the parts of the colon
  • Summarize the internal and external structure of the colon
  • State which parts of the large intestine are responsible for waste removal

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