Glandular Epithelium: Location, Structure, Functions, Examples

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Definition of Glandular Epithelium

In addition to the covering as well as lining epithelium, the glandular epithelium is a collection of tissues which specialise in the production and secretion of various macromolecules. Because of its primary function, the glandular epithelium is also referred to as the secretory epithelium. This epithelium is found beneath the covering and lining epithelium and is composed of either cells with specific roles or glands, which are specialised organs. A gland is composed of epithelium, which secretes substances into ducts (tubes), onto a surface, or, in the absence of ducts, into the blood. Certain unicellular glands composed of specialised cells may exist between the simple cuboidal, simple columnar, and pseudostratified epithelia.

Glandular Epithelium structure

Glandular epithelium develops from the fetus’s covering epithelia by cell proliferation as well as growth into the underlying connective tissue, followed by differentiation.
The cells of the glandular epithelium can be columnar or cuboidal in shape, where squamous cells are not common inside the secretory epithelium.
The endocrine glands’ glandular epithelium has a lot of vascularization as well as innervation.
Proteins (e.g., in the pancreas), lipids (e.g., adrenal, sebaceous glands), or combinations of carbohydrates as well as proteins may be synthesised, stored, as well as released by secretory cells in the glandular epithelium.
Certain gland cells (for example, sweat gland cells) have less synthetic activity as well asproduce mainly water as well aselectrolytes (ions) taken from the circulation.

Glands are further categorized into two groups according to their structure as well as the existence or lack of ducts.

Exocrine glands

Exocrine glands exude their contents into ducts, which then discharge the secretions onto the skin’s surface or the lumen of a hollow organ.
Tubular ducts lined with lining epithelium connect exocrine glands to the covering epithelium, transporting secreted products to the action site.
Exocrine gland secretions have small impact, and some are harmful if they enter the bloodstream.
Exocrine glands can be either single-cell or multicellular in nature. Unicellular exocrine glands are single-celled glands that secrete mucus directly onto the apical surface of the lining epithelium.
Exocrine glands with branched or unbranched ducts are multicellular exocrine glands composed of many cells which create a distinct macroscopic organ.
A secretory unit as well as one or more ducts make up each exocrine gland.
The stroma of connective tissues supports the secretory unit, which is attached to the gland’s duct system.
The structure of the secretory unit as well as whether the ducts are branching or unbranched are used to further categorise the multicellular exocrine glands into kinds.
A simple gland is one which does not have any branching in its duct.
The gland is a complex gland if the duct is branched.
Acinar or alveolar glands are glands with spherical secretory components.
Tubular glands are glands having tubular secretory components.
Tubuloacinar glands are glands which feature both round as well as tubular secretory components.
Exocrine glands are additionally classified into three categories based on the method of secretion release.
The structure of the secretory unit as well as whether the ducts are branching or unbranched are used to further categorise the multicellular exocrine glands into kinds.
A simple gland is one which does not have any branching in its duct.
The gland is a complex gland if the duct is branched.
Acinar or alveolar glands are glands with spherical secretory components.
Tubular glands are glands having tubular secretory components.
Tubuloacinar glands are glands which feature both round as well astubular secretory components.
Exocrine glands are further classified into three categories based on the method of secretion release.
Merocrine glands are glands which secrete their secretions via exocytosis from cells in secretory vesicles.
Apocrine glands are secretory glands which store their secretory product on the apical membrane of the secreting cell as well as then pince off from the rest of the cell to release the secretion.
Finally, the holocrine glands are those in which the cells store the secretory product in their cytoplasm as well asthen burst to release the product when the cell matures.
The secretory units of exocrine glands have a well-developed endoplasmic reticulum, as well as a Golgi apparatus packed apically with secretory granules in various stages of maturity.
various exocrine glands (e.g., sweat, lachrymal, salivary, as well as mammary glands) have contractile myoepithelial cells at the basal ends of the secretory cells in addition to secretory cells.
Actin filaments as well as myosins are plentiful in myoepithelial cells, resulting in the creation of hemidesmosomes which connect the basement membrane and other epithelial cells.
The secretory cell in one type of exocrine gland, known as the holocrine glands, ruptures as well as forms the secretory product as it grows.
A new cell replaces the one which was sloughed off.

Endocrine glands

Endocrine glands are a type of gland which lacks a duct system as well as so releases their secretions straight into the bloodstream.
Hormones, which are secretions from endocrine glands, enter the interstitial fluid as well as permeate into the bloodstream without passing through a duct.
Since endocrine secretions are carried throughout the body by the bloodstream, they have far-reaching effects.
Endocrine glands lose their epithelial connections as well as hence do not have ducts.
Endocrine cells’ produced hormone products are absorbed by thin-walled blood capillaries close to them, which then transport them in the blood to target cells throughout the body.
Endocrine glands’ glandular epithelium lacks myoepithelial cells as well as is specialised for either protein or steroid hormone production.
The endoplasmic reticulum is abundant in glandular epithelial cells, which have a thin cell membrane.
Thin cell membrane wall permits hormones released by secretory cells to diffuse out of the cell.
The binding proteins existing outside of the secretory cells subsequently take the dispersed hormones.
The receptors which indicate the passage of hormones from the glands to the target areas are found either near to the hormone-secreting cells or on the secreting cells themselves.
Endocrine glands are classified into three groups based on their histology:
Trabecular type: The cells in this type are organized in cords, as they are in the liver as well as adrenal glands.
Follicular type: Cells in this type create spherical structures similar to those found in thyroid glands.
Disseminated type: The cells are positioned in clusters or independently in other organs, such as the Leydig cells in the testes, in the disseminated form.The glandular epithelium’s functions

Glandular Epithelium functions

Glandular epithelium’s most important function is secretion.

Secretion

Exocrine glands produce a watery mucus whichFF aids in body temperature regulation as well as homeostasis.
Similarly, glands such as the sebaceous as well as ceruminous glands secrete oily substances which aid to lubricate the surface of the covering epithelium, preventing water loss as well as microbial invasion.
Many metabolic as well as physiological activities are required to sustain homeostasis as well as normal animal function.
Digestive enzymes are generated by the salivary glas well as in the mouth as well as the digestive glands (pancreas) inside the small intestine, which aid in food digestion as well as nutrient absorption.
Hormones generated by the endocrine glands control a variety of metabolic as well as physiological activities in order to keep the animals in a state of equilibrium as well as optimal functioning.
The pituitary as well as thyroid glands, for example, are in charge of the body’s overall growth as well as growth.
Similarly, the adrenal glands are responsible for regulating the metabolism, immunological system, blood pressure, as well as stress response, among other things.
Reproductive system’s ovary as well as testes create the gametes required for sexual reproduction.
Thymus gland in the thoracic cavity is in charge of producing T-cells, which are responsible for removing foreign antigens from the body.

Glandular epithelium examples

Examples of glandular epithelium include the pituitary gland at the base of the brain, the pineal gland as well as in the brain, thyroid and parathyroid glands near the larynx (voice box), adrenal glands superior to the kidneys, pancreas near the stomach, ovaries in the pelvic cavity, testes in the scrotum, and thymus in the thoracic cavity.
Exocrine glands include the sweat, sebaceous, and ceruminous glands of the skin, as well as digestive glands such as the salivary glands and pancreas.

Glandular epithelium Citations

Tortora GJ and Derrickson B (2017). Principles of Physiology and Anatomy. Fifteenth Edition. John Wiley & Sons, Inc.
Waugh A and Grant A. (2004) Anatomy and Physiology. Ninth Edition. Churchill Livingstone.
Stefan TOTH. Glandular epithelium. Department of Histology and Embryology, P.J. Šafárik University, Medical Faculty, Košice.
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https://fac.ksu.edu.sa/sites/default/files/glandular_epithelium_2019_1st_semester_1.pdf
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