Epithelial tissue covers the entire surface of the human body. Besides, it also covers the internal organs. The epithelial tissue that is present in the interior of the body is called endothelium. This tissue is also called a vascular tissue as there is no direct supply of blood to this tissue. It is also one of the most simple tissues with a primitive structure. There are two major categories of epithelial tissues: (i) simple epithelial with a single layer of cells; (ii) striated epithelial with two or more layers of cells. It can be further subdivided depending upon the shape and function of the cells. Glandular epithelium is a type of striated epithelial tissue that covers the organs associated with secretion.
Glandular epithelium forms the covering of all major glands. It is also present in the intestinal lining. There are two major types of glands: endocrine and exocrine. Endocrine glands are associated with the secretion of substances that are internally used by the body, e.g. hormones. Exocrine glands secrete substances that are to be excreted by the body, e.g. mucus, sweat, etc. Endocrine glands release their secretions directly in the bloodstream, from where they travel to the target organs, whereas exocrine glands reach the target organs through the medium of ducts. Both of these glands produce their secretions through the glandular epithelium tissue, which comprises several specialized cells called goblet cells.
One peculiar characteristic of epithelial cell is that they are closely packed together, with little or no intracellular space. The cells are cuboidal in shape with multiple layers. A basement membrane is always present, which separates the epithelial tissue from the other tissues. The cells are uninucleate with a single large nucleus. Cells are filled with substantial amount of clear, transparent cytoplasm. The cells multiply by the process of simple mitosis.
Secretion is the main function of glandular epithelium. It consists of goblet cells that specialize in synthesis and secretion of several chemicals. Even the normal columnar epithelial cells specialize in the synthesis of chemicals such as enzymes, hormones, milk, mucus, sweat, wax, and saliva. Glandular epithelium present in the intestinal lining helps in the absorption of nutrients. Thus, it assists in the process of digestion. Glandular epithelium in the exocrine glands secretes mucus, which is transported by the network of ducts. Endocervical glandular epithelium is associated with various sexual functions. It includes secretion of lubricating fluids during sexual excitement. Besides, it is also concerned with various reproductive functions.
Mode of Secretions in Glandular Epithelium
There are basically three modes of secretion in glandular epithelium.
» Merocrine secretion is a type of secretion where the secretory substance in the cytoplasm of the cells is collected in the apical region of the cell. Then the contents are released along with the fusion of the membrane.
» Apocrine secretion includes discharge of the content by breaking down the lumen of the cell. This type of secretion mainly involves sex hormones that activate around puberty.
» Holocrine secretion is a type of secretion in which the cell becomes bloated by the secretory product and then disintegrates to become a part of the secretory product.
To summarize it all, glandular epithelium is a multifunctional epithelial tissue. It combines with the other tissues of the body to perform various vital functions in the body. Any abnormality in this tissue directly leads to the dysfunction of the concerned gland.