This is a low power image of the colon. Can you can identify the mucosa, submucosa and muscularis externa.
The large intestine completes absorption, and retrieves water and sodium from the luminal contents which become fecal residue. It secretes large amounts of mucus, and some hormones, but no digestive enzymes.
The thick mucosa has deep crypts, but there are no villi. The epithelium is formed of columnar absorptive cells with a striated border, many goblet cells, endocrine cells and basal stem cells, but no Paneth cells. The surface epithelial cells are sloughed into the lumen, and have to be replaced around every 6 days.
The lamina propria and submucosa are similar to the small intestine.
The longitudinal smooth muscle in the muscularis externa is arranged in three longitudinal bands called taenia coli. At the anus, the circular muscle forms the internal anal sphincter.
This is a magnified image of the mucosal layer.
Can you identify the epithelium, and muscularis mucosa.
You can also see lymphoid cells in the lamina propria layers. The pale staining cells that line the mucosa form tubular glands, that secrete mucus. Some of these cells are absorptive cells. Stem cells are also present. It is hard to distinguish these different cells types in this image.
Compare the epithelia of the oesophagus, stomach, duodenum, small and large intestines