The ileum is the distal section of the small intestine, which is divided from the large intestine by the ileocecal valve. The inner surface of the ileum is covered with small finger-like appendages known as villi. Epithelial cells that line the villi feature numerous microvilli, further increasing the surface area of the ileum. The large surface area of the structure is important for maximizing the adsorption of enzymes and the absorption of nutrients. Enzymes secreted by the epithelial cells are essential for the final steps of carbohydrate and protein digestion. Blood is supplied to the ileum by the superior mesenteric artery and its branches.

The rat ileum has been featured in a wide variety of studies. In recent years, for instance, scientists have investigated such topics as the effects of stress and radiation on the paracellular barrier in the rat ileum, as well as alterations produced in the rat ileum by diabetes and lead. Such research can provide valuable information regarding potential risks to the intestinal health of humans.

In the digital image above, a sample of rat ileum tissue is presented that was labeled with the fluorophore Texas Red conjugated to wheat germ agglutinin, a fluorescent lectin that selectively binds to sialic acid residues. Wheat germ agglutinin conjugates are often used as probes for the Golgi network in mammalian tissues and cells. The sample was also stained with Alexa Fluor 488 conjugated to phalloidin and Hoechst 33342, which target the cytoskeletal filamentous actin network and nuclear DNA, respectively. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.

Triple Staining of Ileum Section with Alexa Fluor 568, Oregon Green 488, and Hoechst 33342 - In the human adult, the ileum is typically about 12 feet long and the entire small intestine is approximately 21 feet long. In contrast, the human large intestine has a length of about 5 feet. The proportional relationships between the intestinal sections of other species vary, however, generally reflecting differences in diet.

Sialic Acid Residues, F-Actin, and Nuclear DNA in a Rat Ileum Tissue Specimen - During early embryonic development, the ileum is linked to the umbilicus via the vitelline duct. By the time a human fetus is seven weeks old, the vitelline duct is has completely atrophied. If the duct does not atrophy, a number of medical abnormalities can arise. The most common of these aberrations is Meckel's diverticulum, which occurs when the part of the duct connected to the ileum is retained.