Describe the types and functions of Glandular epithelium.

(N/A) $\Rightarrow$ Glandular epithelium: Some of the columnar or cuboidal cells get specialized for secretion and are called Glandular Epithelium.
$\Rightarrow$ They are mainly of two types based on the number of cells:
$(i)$ Unicellular glandular epithelium: It consists of isolated glandular cells (e.g., goblet cells of the alimentary canal).
$(ii)$ Multicellular glandular epithelium: It consists of a cluster of cells (e.g., salivary gland).
$\Rightarrow$ On the basis of the mode of pouring of their secretions, glands are divided into two categories:
$(i)$ Exocrine glands: These glands secrete mucus, saliva, earwax, oil, milk, digestive enzymes, and other cell products. These products are released through ducts or tubes.
$(ii)$ Endocrine glands: These glands do not have ducts. Their products, called hormones, are secreted directly into the fluid bathing the gland.