Ileum - 40X
 
The ileum is the part of the small intestine that empty into the large intestine. The submucosa of the small intestine contains lymphoid nodules that look like the ones you saw in the lymph node. They are called Peyer's patches. In this image the mucosa is on the right. The dark band along the right side is the location of this lymphoid tissue. Although the lymphatic nodules are located throughout the small intestine, they are most abundant in the ileum.

The two layers of smooth muscle in the muscularis are very clear in this image. The inner layer is made of cells that are arranged circularly (circ) and the outer layer cells are arranged longitudinally (long).

Ileum, thin-section - 40X
 
Because the Peyer's patches (pp) contain many lymphocytes (a type of white blood cell) they stain very darkly. They are part of a larger group of lymph nodules called the mucosa-associated lymphatic tissue that are present in other parts of the digestive system and the respiratory system.





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