IMAGE 1 - Esophagus, low-power
Image 1 is a low-power cross section of the esophagus. Except for the mouth, the esophagus is the only organ not in the abdominal cavity. Anatomically, the esophagus is an entrance into the abdominal digestive organs. Because it is not in the abdomen, it is not covered in the peritoneal membranes. It travels posterior to the pericardium. Instead of having a serous covering, the outer portion of the tube is covered in a fibrous layer called the tunica adventitia. Functionally, the esophagus secretes a mucus and uses muscular tissues to create gastric motility in the form of peristalsis. The mucosa is covered with a stratified epithelium. The mucus and stratified mucosa act to protect the esophagus from damage from large, undigested pieces of food.
Image 2 - Esophagus, high-power
Image 2 is a high-power view of a cross section of the esophagus. You can see the detail of the stratified epithelium in the mucosa much better. At this magnification you can see the blood vessels, in this image you can see several open lumens labeled with blue circles in the image. The two lines from the star indicate submucosal glands that secrete mucus. The majority of the tissue in the submucosa is dense regular connective tissue.
Image 3 - Stomach, low-power
Image 3 is a cross section of the mucosal side of the stomach. The lumen is towards the bottom of the slide. The layers labeled B and C make up the mucosal layer. Notice that the surface of the mucosa does not project out into the lumen, instead there are deep invaginations, or folds, into the mucosal surface. The muscularis mucosa is labeled C in the image and defines the barrier between mucosa and submucosa.
Image 4 - Stomach, high-power
Image 4 is a high-power cross section of the mucosa of the stomach. The mucosa is lined with simple columnar epithelia. Folding is usually a sign of increased surface area; however, in the stomach, because the folds are inwards it reduces the surface area that is actually exposed to the lumen of the stomach. Even though food is not very well digested in the stomach, this arrangement would make absorption of nutrients ineffective.
Image 5 - Small Intestines, low-power
Image 5 is a low-power cross section of the small intestines. Compared to the stomach, we see the mucosa has changed so that now we see long finger-like villi projecting into the luminal space.
Image 6 - Small Intestines, high-power
Image 6 is a high-power view of the small intestine. The large white circles are mucus secretions. Notice the alternating dark/light purple staining within the columnar cells that line the lumen, this is indicative of cells that are producing secretions. The brush borders would indicate large surface area. The mucosal lining of the small intestines provide protection for the underlying tissues, secrete enzymes, and provide surface area for absorption.
Image 7 - Duodenum, high-power
Image 7 shows the duodenum. The circular structures at #7 are Brunners glands. These glands produce bicarbonate to buffer the stomach acids and protect the mucosal lining of the small intestines.
Image 8 - Colon
Image 8 is a cross section of the colon. This arrangement is much more like the stomach, there are no villi, just deep folds into the mucosa. There are many goblet cells producing the white mucus secretion that allows dehydrated fecal material to move through the colon.
Image 9 - Peyer's Patch in Colon
In image 9, the arrow points to a large lymph node-like structure in the colon. Motility is low in the colon and bacteria start to multiply. These lymph areas allow for immune defense against pathogens, similar to tissues in actual lymph nodes, tonsils, and the spleen.