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Organ system histology
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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. 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.
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.
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