Basic introduction Chinese name: Wool mbth: underfur Explanation: Soft and slender hair nickname: basic definition of fine hair, medical significance, basic definition Pinyin: [róng máo] English: underfur Explanation: Soft and slender hair, also called fine hair. Main production bases: Zhejiang Puyuan, Guangdong Da Lang, Hebei Qinghe, etc. Medical significance is also called flexible process. Dense cell clusters with finger-like or dendritic protrusions can significantly increase the surface area on the intestinal mucosa of vertebrates or the contact surface between placenta and uterine wall of mammals, which is beneficial to absorption. The surface of villi is covered with epithelial tissue and there is a capillary network inside. Epithelial cells on the surface of villi have many protoplasms (microvilli) on their free surfaces, so their surface area increases. The surface of villi is a single columnar epithelium, and the central axis is the lamina propria. Epithelium consists of columnar cells, goblet cells and a few endocrine cells. The central axis of villi contains many lymphocytes, plasma cells, macrophages and mast cells. There is a central chylous duct in the center of villi, and there are abundant porous capillaries around it. There are also smooth muscle fibers in villi. The function of fluff can swing. The villi on the inner wall of small intestine is the characteristic structure of small intestine, which is formed by the protrusion of mucosal epithelium and lamina propria to the intestinal cavity. The function is to enlarge the surface area of small intestine, which is beneficial to the absorption function of small intestine.