How are epithelial cells classified?

Epithelial cells are classified into various categories based on their shape, arrangement, and specialized functions.  

Based on Cell Shape:

1. Squamous Epithelial Cells: Squamous epithelial cells are flat and scale-like in shape, resembling a continuous sheet. 
2. Cuboidal Epithelial Cells: Cells are cube-shaped, with equal height, width, and depth.
3. Columnar Epithelial Cells: Cells are taller than they are wide, resembling columns.

Based on Cell Layer Arrangement:

1. Simple Epithelium: Consists of a single layer of epithelial cells that line surfaces where absorption, secretion, and filtration occur.
2. Stratified Epithelium: Comprises multiple layers of epithelial cells, providing more protection and durability. This type is found in areas subjected to mechanical stress.
3. Pseudostratified Epithelium: Epithelial cells in the pseudostratified epithelium are closely packed and arranged in one layer. The varying cell heights create the illusion of stratification. The surface of these epithelial cells often feature cilia. 

Based on Specialized functions:

1. Transitional Epithelium: Found lining most of the urinary tract, transitional epithelium is composed of multiple layers of cells that become flattened when stretched, which allows the bladder to expand and contract without compromising its structure or function.
2. Glandular epithelium: Found lining the glands, the glandular epithelium is specialized to synthesize, store, and release various substances such as water, hormones, and proteins. 
3. Olfactory epithelium: Situated within the nasal cavity, the olfactory epithelium is home to olfactory receptor cells, which are equipped with unique cilia extensions. These cilia serve to capture odor molecules when you inhale, allowing them to traverse the epithelial layer. Subsequently, the receptors convey information about these molecules to the olfactory bulb in your brain, where the scent is interpreted and recognized.