Write a note on glandular epithelium

The shape of the cells of this tissue is columnar but they secrete some substance. These cells form a gland. According to the structure the glands may be of following types:
(i) Unicellular glands : Goblet cells in the intestine epithelium are example of this type of gland.
(ii) Multicellular glands : These are made of many glandular cells. They may be alveolar or tubular (Brunner’s glands). The salivary glands of mammals are tubular but are compound multicellular glands.