False-colour scanning electron micrograph of a section through the wall of the human duodenum, showing the many tiny folds, known as villi, which project 0.5 to 1 mm out into the intestinal lumen. These folds greatly increase the effective absorptive and secretory surface of the mucosa (mucus membrane) which lines the small intestine. Each villus contains a central core of connective tissue (yellowish orange), known as the lamina propria. This contains large blood vessels, capillaries, some smooth muscle cells and a blind- ended lymph vessel known as a lacteal. Magnification: x50 at 6x6 cm size.