Colon histology

Definitions & Key takeaways

The colon is a section of the large intestine that helps to absorb water and electrolytes from food matter, and it also helps to store fecal matter until it can be eliminated from the body. The colon has three sections: the ascending colon, the transverse colon, and the descending colon. The ascending colon is located on the right side of the body, while the descending and transverse colons are on the left side. The wall of the colon has four layers. There is an inner layer called mucosa, a middle layer called submucosa, a muscular layer called muscular externa, and an outer layer called serosa.

The mucosa has enterocytes, the intestines' absorptive cells. These are simple columnar cells with microvilli, responsible for absorbing water and nutrients, and goblet cells secrete mucus. The submucosa contains connective tissue, blood, lymphatic vessels, and a network of nerves known as Meissner's plexus. The muscularis mucosa comprises two layers of smooth muscle tissue that contract and relaxes to help move food matter through the colon. The serosa is a thin layer of tissue that covers the outside of the colon and helps to protect it from infection. The colon is home to many different types of bacteria that help to break down food matter and extract nutrients from it. These bacteria also produce vitamins and other compounds that benefit the body. In addition, the colon plays an essential role in the immune system by producing antibodies that help to fight off infection.

Chapters:

Watch video only

Introduction0:00–0:35

Now, let's get a closer look. The large intestine consists of the appendix, cecum, colon, rectum, and anal canal.
The colon is mainly responsible for reabsorbing water and electrolytes from the feces within its lumen. The colon is continuous with the rectum, where the feces is stored before defecation.
Similar to the rest of the large intestine, the colon has 4 main layers: the mucosa, submucosa, muscularis propria, and a surrounding serosal layer of connective tissue that isn’t seen in this image.Even at low magnification, we can see that the colon’s mucosa at the top of this image doesn’t have the distinct long villi or finger-like projections that would normally be seen in the small intestine.

Tissue layers0:35–4:19

Taking a closer look at the colon’s mucosa, the lumen of the colon is seen at the top of the image and the first layer of cells lining the mucosa is the epithelium of the mucosa.
The epithelium consists of two types of cells, enterocytes and goblet cells. The enterocytes or absorptive cells are the simple columnar cells with microvilli.
They’re also called the absorptive cells because of their main function of absorbing water from the colon lumen. And the goblet cells are responsible for secreting mucus.
Although the cells aren’t clearly seen in this image, the mucus they produce is easily seen as the globular structures that are stained dark purple from the hematoxylin and eosin stain.
The surface epithelium is continuous with straight, unbranched, tubular glands called the crypts of lieberkühn. Unlike the crypts in the small intestine, these crypts extend through the majority of the mucosa, from their openings at the intestinal surface all the way to the muscularis mucosa along the deepest portion of the overall mucosa.
It may not always appear to be continuous on histological slides because the path of the crypts may not always travel along the same plane as the section of tissue taken from the colon.
The superficial portions of the crypts will typically have a higher concentration of enterocytes and the deeper portions will have a high concentration of goblet cells.
The tissue found between the crypts and the epithelium is the lamina propria, which consists of many types of immune cells, including plasma cells, lymphocytes, eosinophils, and macrophages.
And finally, the deepest layer of the mucosa is a thin layer of smooth muscle called the muscularis mucosa.Beneath the mucosa is the next major layer of the colon, the submucosa.
This layer consists mostly of dense irregular connective tissue, but also contains blood vessels, lymphatic vessels, and the submucosal or meissner’s plexus.
Meissner’s plexus is a network of nerves that innervate the goblet cells in the mucosa as well as the smooth muscle of the muscularis mucosa.
In this image, there’s a relatively large cross-section of a bundle of nerve cells that are part of meissner’s plexus. We can also see a number of large blood vessels and a lymphatic vessel in the upper left of this image.Surrounding the submucosa is the next main layer of the colon wall called the muscularis propria or muscularis externa.
The thick muscularis propria allows the colon to have strong peristaltic or wave-like contractions to help move the feces through it’s lumen.
The inner layer of smooth muscle is arranged circularly or circumferentially around the colon’s wall, and the outer layer of smooth muscle is arranged longitudinally along the length of the colon, but it’s also arranged into 3 long bands of muscle called teniae coli.
Between the two layers of muscle, we can see cross-sections of nerves from another network of nerves called the Myenteric or Auerbach’s Plexus, which is responsible for innervating the muscle fibers of the muscularis propria.
Also, some portions of the colon will have an additional thin layer of connective tissue that surrounds the muscularis propria called the serosa.Alright, as a quick recap… the colon has 4 main layers: the mucosa, submucosa, muscularis externa, and the outermost layer of serosa.

Review4:19–5:13

The mucosa is comprised of an epithelium, lamina propria, crypts of lieberkühn, and muscularis mucosa. The submucosa consists of dense irregular connective tissue, blood vessels, lymphatic vessels, and meissner’s plexus.
The muscularis externa is a thick layer of smooth muscles with an inner circumferential layer and an outer longitudinal layer that’s organized into 3 bands of smooth muscle called teniae coli.
Between the layers of smooth muscle is the myenteric plexus, which is the network of nerves responsible for innervating the smooth muscle of the muscularis propria.
And the final, outermost layer is the serosa, which is a thin layer of connective tissue that also