Pseudostratification

Pseudostratification is a cellular feature characterized by the appearance of multiple layers of cells when viewed under a microscope, even though all cells are actually attached to a single basement membrane. This occurs when cell nuclei are found at different levels within the epithelium, creating the illusion of stratification. In true stratified epithelia, multiple layers of cells are present, with cells in the superficial layers not in direct contact with the basement membrane.

Pseudostratified epithelia are typically found lining organs where secretion or absorption is important, and where the movement of substances across the surface is facilitated by cilia. A classic example is the pseudostratified columnar epithelium that lines the trachea and other parts of the respiratory tract. Here, the cilia beat rhythmically to move mucus and trapped debris away from the lungs. Another common type is pseudostratified ciliated columnar epithelium with goblet cells, which produce and secrete mucus.

Despite its layered appearance, a key diagnostic feature of pseudostratification is that every cell, regardless of its nuclear position, is in contact with the basement membrane. This distinguishes it from true stratified epithelia. The varying heights of the cells and the irregular arrangement of their nuclei contribute to the characteristic pseudostratified look. This arrangement allows for a greater number of organelles to be present within the cells, supporting their specialized functions.