Final answer:
The type of epithelium lined with dense microvilli in the intestines and kidney tubules is the simple columnar epithelium, which increases the available surface area for absorption and reabsorption of nutrients and substances.
Step-by-step explanation:
The type of epithelium you would find lining the intestines and kidney tubules densely packed with microvilli is simple columnar epithelium. In the intestines, specifically the small intestine, this epithelial tissue greatly increases the surface area for absorption of nutrients from digested food. Similarly, in the kidney tubules, the microvilli increase the surface area for reabsorption of vital substances back into the blood. The presence of microvilli on the epithelial cells is a key feature for efficient absorption and secretion in these organs. The role of microvilli in nutrient absorption is quite significant, as they expand the surface area available for absorbing nutrients from the chyme, which is the semi-fluid mass of partly digested food that is passed from the stomach to the small intestine. Therefore, they are crucial for the efficient operation of the digestive system.