Large Colon and Ulcerative Colitis

The Large Intestine

It's very important that UCers understand where the large colon is and how it works. I've found that being more knowledgable about it has led to: a better understanding of which type of colitis I have; more precise explanations for Doctors; a better awareness of what area is effected by treatments, diet changes etc.; an increased awareness of what might happen e.g. how long before a bowel movement if there is a cramp somewhere along the large intestine.

Digestive System

First lets look at where the large colon is in relation to the digestive system. The Digestive System is a term used to include all aspects; from the mouth through to the anus. You may hear it referred to as the Gastrointestinal tract or GI by Doctors, specialists and at hospitals (although technically the GI is the stomach and intestines only).

As you can see from the diagram on the right, there are quite a few aspects to the digestive system. I've simplified it down to 5 parts because I don't think complex details are important when trying to learn about Ulcerative Colits - especially as the last section is the area most UCers are concerned with!!


  1. Food is broken down in the mouth by chewing, and is swallowed
  2. Food then travels down the throat (Oesophagus)
  3. Food enters the stomach where it's partially digested by stomach acids
  4. The partially digested food enters the small intestine where most of the digestion and absorption of nutrients, vitamins and minerals takes place
  5. Finally, the remaining waste 'food' moves into the large intestine where some water and electrolytes are absorbed before expulsion

Digestive System Digestive System

Large Intestine Sections

The Ascending Colon

This is the section of the large colon that's on the right side of the abdomen. I've read questions by UCers asking whether the pains they were getting on the right were anything to do with colitis - this shows that they can be.

It's also worth noting if symptoms are at the top or bottom of the Ascending colon as well; you can really start pinpointing which areas might be inflammed with this knowledge.

Pancolitis affects this area and may also effect other parts of the large colon.

Ascending Colon and Ulcerative Colitis

The Transverse Colon

This is the section of the large colon that crosses the abdomen. Because of its location, aches and pains in this part of the colon are often mistaken for the stomach which actually sits just above.

When the transverse colon is inflammed, the location of aches and pains tend to occur across the bottom of and/or just underneath the rib cage.

Pancolitis affects this area and may also effect other parts of the large colon.

Transverse Colon and Ulcerative Colitis

The Descending Colon

The Descending colon is located down the left side of the abdomen.

When the Descending colon is inflammed, the location of the aches and pains tend to occur down the left side of the abdomen.

Left-sided colitis affects this area only.

Descending Colon and Ulcerative Colitis

The Sigmoid Colon

The Sigmoid colon is located more or less along the bottom left side of the abdomen.

When the Sigmoid colon is inflammed, the location of the aches and pains tend to occur next to or below the belly button.

Proctosigmoiditis affects this area only.

Sigmoid Colon and Ulcerative Colitis

The Rectum

The Rectum is located in the centre, below the abdomen and further back.

When the Sigmoid Rectum is inflammed, the location of the aches and pains can feel like they are below the belly button and/or also at the back of the body, nearer the exit. Inflammation in this area also causes the worst cases of urgency due to the close proximity to the exit.

Proctitis affects this area only.

Ascending Colon and the Rectum

The Large Intestine

The last part of the digestive system is called the Large Intestine. The Large Intestine (approx 1.5 metres long) loops all the way around the abdomen, almost framing it. It contains the Cecum, the Large Colon and the Rectum and makes up about a fifth of the entire intestinal length.

Because the large intestine wraps around, it's possible to get pains on the right side, across the middle or down the left side of your abdomen.

It's also interesting to note how close the stomach is to the transverse colon. Quite a few UCers make the mistake of thinking they are having stomach aches when it's actually the transverse colon - I made the same mistake at first.

Side View

I think it's also worth showing a side view of the large intestine because it's interesting to see how far back it goes.

I always imagined that the colon ran around the front of the internal system, but as you can see, both the ascending and descending colon are set further back, on the edge of and behind, the small intestines.

I've read comments by UCers asking about pains in their side or back - this view shows that it's possible certain sections of the ascending or descending colons are the reason behind them.

Large Colon / Large Bowel / Large Intestine Large Colon / Large Bowel / Large Intestine - Side View

How the Colon Works

The large intestine is basically a hollow tube with muscles along it to move waste, although the tube actually has many layers. It doesn't produce any digestive enzymes, and the pH is 5.5 to 7.0, which is slightly acidic.

  • Electrolytes are absorbed by mucosa that line the inner wall - the waste touches them as it moves through. This absorption mainly takes place in the cecum and ascending colon
  • Water is absorbed gradually which leads to firmer and more formed stools by the time it moves into the descending colon - A fresh, healthy stool when it leaves the body is approximately 75% water.
  • Vitamins are produced by 'friendly' bacteria in the colon.

The main function of the large colon is to absorb any remaining nutrients and water from the waste before removing it. It absorbs electrolytes (mainly sodium & potassium) and vitamins (K and B7) which are produced by bacteria in the large colon.

Vitamin K is particularly important because the amount taken daily from food is generally not enough for blood coagulation (clotting). When considering the ulceration caused by colitis, it seems obvious then, that a lack of vitmain K will go hand in hand with the disease. The fact that vitamin K helps our blood to clot could be part of the reason that UCers experience blood.

In a healthy person about 10% of the water and vitamins used by the body are absorbed through the colon. However, When dietary intake is too low, vitamins used by the body which are absorbed through the large colon contribute significantly.

Colitis sufferers often have a limited dietary intake and are also unable to absorb vitamins from the colon due to inflammation - this can cause problems such as diarrhea, dehydration and a deficiency in some vitamins and minerals.

Studies have shown that sufferers of Ulcerative Colitis and Crohn's disease absorb less sodium and water and secrete more potassium. Also, with distal colitis the permeability of the rectosigmoid (rectum and sigmoid) colon is reduced, which gives an insight into the mechanism of diarhhea.

To compound things further, if people with a limited dietary intake are given antibiotics, the helpful bacteria that produce vitamins can be destroyed, resulting in further deficiencies. The colon contains over 700 species of 'friendly' bacteria some of which aid digestion or produce fat soluble vitamins.

There are estimated to be over 100 trillion microbes in the gut, which means humans are made up of many more microbes than genes, and it's why the gut microbiome is an interesting area of research.

Large Colon - How it Works Large Colon - How it Works

Haustra (Segments) - Peristalsis (waves)

The colon appears to have lots of segments along it, these are collectively called haustra. A single haustrum is a small pouch which slowly contracts approximately every 25 minutes. The effect is that of a slow wave which moves the contents along to the next pouch and so on. Loss of the haustra is a sign of chronic ulcerative colitis.

These involuntary waves (they happen without us thinking about it) are known as peristalsis (I prefer to call it flexing!!). The waves can be the reason behind painful cramps that UCers experience.

Small waves occur throughout the day, large waves occur en masse 1 to 3 times per day, propelling waste from the large colon to the rectum.

Large Colon Haustra