A form of epithelial tissue is the simple epithelium.
Simple epithelium is further divided into three types based on the structural modifications of the cells. Squamous, Cuboidal, and Columnar are the three types.
Glandular epithelium:
It is made up of some columnar or cuboidal cells that have been specialized for secretion.
They are divided into two types: unicellular glandular cells (consisting of isolated glandular cells) and multicellular glandular cells (clusters of cells).
Example of the unicellular gland - goblet cell of the alimentary canal
An example of the multicellular gland - is the salivary gland.