Sinusoidal cells are specialized cells found in certain organs, such as the liver and spleen. They are characterized by their irregular, sinusoidal shape, which allows for the efficient exchange of substances between blood and surrounding tissues. These cells play a crucial role in filtering blood and supporting immune functions. In the liver, sinusoidal cells include Kupffer cells, which are macrophages that help remove pathogens and debris from the blood. In the spleen, sinusoidal cells assist in the filtration of blood, contributing to the body's immune response by facilitating the interaction between blood cells and the immune system.