The inner wall of the small intestine is lined with epithelial tissue covered in wrinkles and folds from which villi — microscopic fingerlike pieces of tissue — project, increasing the surface area for absorption. (protomag.com)
At the end of a meal, specialized endocrine cells in the wall of the small intestine release other hormones (like cholecystokinin, glucagon - like peptide - 1, and oxyntomodulin) that signal satiation. (discovermagazine.com)
In one type of refractory celiac disease, called RCDII, immature white blood cells from the immune system (called lymphocytes) which are located in the wall of the small intestine, multiply in number in an uncontrolled manner. (sciencedaily.com)