Villi: Villi are small, finger-shaped folded projections in the small intestine, covered with even smaller microvilli on their epithelial cell membranes. They are then connected to the circulatory system. Their main function is to increase surface area of the intestines, giving nutrients more space to absorb through the digestive tract and into the bloodstream. This in turn speeds up the process of absorption.
Smooth muscle: Smooth muscle is an involuntarily-controlled muscle characterized by non-striated muscle tissue. In this case, it lines the digestive tract, including the small intestine. Its main function in the small intestine is peristalsis, which is the periodic contraction and relaxation of the muscle in a wave-like pattern, in order to move food through the digestive tract. Of course, gravity helps as well!
Intestinal glands: There are many intestinal glands in the small intestine epithelium, including goblet cells, endocrine, and other secretory glands. Some cells secrete digestive enzymes to break down carbohydrates, proteins, and fat. Remember, the small intestine is where most digestion and absorption occurs! Goblet cells secrete mucous that is vital to the innate immune system, making the surface too slippery for pathogens to colonize, as well as protecting the small intestine from destroying itself. The endocrine cells secrete hormones to help regulate the process of digestion and absorption in other digestive organs.
