Answer :
Epithelial tissues are categorized based on the shape of the cells (squamous, cuboidal, columnar) and the number of cell layers (simple, stratified, pseudostratified, transitional). They are avascular and exhibit polarity, with cells possessing apical, basal, and lateral surfaces including tight junctions.
The question pertains to the classification of epithelial tissues in the human body. These tissues are typically classified by two main characteristics: the shape of the cells and the number of cell layers they form. The three primary cell shapes are squamous (flattened and thin), cuboidal (as wide as it is tall), and columnar (taller than it is wide). Based on the number of layers, epithelial tissues can be either 'simple' if there is a single layer or 'stratified' if there is more than one layer. A pseudostratified epithelium may appear to have multiple layers, but it is actually a single layer of irregularly shaped cells, while transitional epithelium undergoes shape changes as it stretches.
When observing a tissue sample under a microscope, it is important not to assume that one is looking at epithelial tissue just by finding one end of the sample. Instead, one should seek the specific cellular characteristics that define epithelial tissues, such as their polarity, the presence of tight junctions, and their attachment to a basement membrane. Furthermore, epithelial tissues exhibit avascularity, meaning they do not have blood vessels supplying them directly.
