Transmission electron micrograph (TEM) of the ultrastructure of apposed microvilli of two enterocytes of the small intestine epithelium. Microvilli are finger-like projections of the apical surface membrane of intestinal absorptive cells. They are about 1 micrometre in length with a core of actin filaments and greatly increase the membrane surface area for absorption of nutrients in the intestinal lumen. Fluid secretion by enterocytes also occurs across the microvilli. Magnification: x10,000 when width printed at 10cm.