The Ileum is the final 2/3 of the small intestine. A key identifier of the ileum is the abundance of large payer's patches--collections of lymphocytes for defense. While these may be found throughout the small intestine, only the ileum has them in abundance.
The mucosa of the ilium consist f vili with abundant goblet cells and a lamina propria of areolar connective tissue.
Intestinal crypt region of the ileum. these are regions between the vili. Note the peyers patch in the submucosa, as well as the well developed muscularis mucosae.
Paneth Cells (red) secrete anti-bacterial "granules" as part of the immune response to potentially invading bacteria.