Simple Columnar Epithelium: Definition, Structure, Functions, Examples

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Definition of a Simple Columnar Epithelium

The simple columnar epithelium is a type of epithelium made up of a single layer of long, elongated cells found primarily in locations where absorption and secretion are important. The cells in the columnar epithelium, like those in the cuboidal epithelium, are changed to better suit the organ’s function and structure. The simple columnar epithelium is either ciliated or non-ciliated, and the non-ciliated columnar epithelium has microvilli on the apical area.

Simple Columnar Epithelium Structure

The simple columnar epithelium is composed of a single layer of elongated cells that are always taller than they are wide and are linked directly to the basement membrane at the distal end.
The nucleus is oval and big, and it is located at the cell’s base.
The cells are closely packed together, and goblet cells can be found in the non-ciliated columnar epithelial layer.
A vast number of organelles are also present in the cells of the columnar epithelium. As a result, they are capable of more secretion and absorption than cuboidal cells.
The apical surface of the cells in the columnar epithelium is directed toward the lumen of the organs or ducts, as in all other types of epithelial tissues, but the lateral surface is equipped with adhesions and junctions to promote the connection between adjacent cells.
At the apical extremities of the cells, complexes of tight and adherent junctions, commonly referred to as “terminal bars,” arise.
There is no direct blood supply to the cells in the basic cuboidal epithelium. Even so, because they are intimately linked to the basement membrane, they obtain their nutrition, water, and gases from the underlying tissue via diffusion.
The cells, on the other hand, are innervated and have a nerve supply.

The simple columnar epithelium is divided into two categories based on the presence or absence of cilia: Non-ciliated columnar epithelium and Ciliated columnar epithelium.

Non-ciliated Simple Columnar Epithelium

A single layer of non-ciliated columnlike cells with oval nuclei near the base of cells makes up the non-ciliated simple columnar epithelium.
Columnar epithelial cells with microvilli on the apical surface and goblet cells make up the cell layer.
Microvilli are cytoplasmic projections that are located on the apical surface and direct towards the organ’s lumen.
The average microvillus is around 1 m long and 0.1 m wide, but because hundreds to thousands of them are present on the end of each absorptive cell, they can increase the surface area by 20 or even 30 fold.
Actin-binding proteins cap and bind bundled actin filaments to the surrounding plasma membrane in each microvillus.
Membrane-bound proteins and enzymes for the digestion of particular macromolecules are found in the thick glycocalyx that covers the microvilli of the intestinal columnar epithelium.
Goblet cells are modified columnar epithelial cells with apical surfaces that release mucus, a slightly sticky fluid.
Mucus builds up in the upper region of the cell before it is released, causing it to bulge and resembling a goblet or wine glass.

Columnar Epithelium with Cilia

The ciliated simple columnar epithelium is made up of a single layer of ciliated column-like cells with oval nuclei near the base of the cells, with goblet cells interspersed between them.
The cilia are usually 5-10 metres long and 0.2 metres wide. The core structure of each cilium is made up of nine peripheral microtubule doublets surrounded by two central microtubules.
Cilia have rapid beating patterns that carry a stream of fluid and suspended particles down the epithelium in one direction.

The Simple Columnar Epithelium Functions:

Secretion, absorption, protection, and transportation of molecules are the basic functions of the simple columnar epithelium.Absorption and secretion are the fundamental functions of the non-ciliated columnar epithelium. The ciliated columnar epithelium, on the other hand, facilitates in the transport of chemicals and cells from one location to another.

Absorption

The function of absorption is considerably boosted by the microvilli found on the apical surface of the non-ciliated columnar epithelium, which increases the surface area.
The non-ciliated columnar epithelium of the gastrointestinal system, which extends from the stomach to the anus, is responsible for macromolecule and water absorption.
Accessory membrane-bound proteins are also given to the cells, which aid in the active absorption of these nutrients.

Secretion

The goblet cells of the tissue secrete mucus, which lubricates the linings of the digestive, respiratory, and reproductive tracts, as well as the majority of the urinary tract.
The mucus in the respiratory tract protects against foreign particles and stops them from entering the inner respiratory tract through the nasal tube.

Protection

The simple columnar epithelium also serves as a protective barrier, shielding luminal chemicals from non-specific movement.
The apical portion of the cells has a series of junctions that limit the movement of molecules and ions across the intracellular compartments.
This also inhibits dangerous big macromolecules from entering the body.
Similarly, the mucus released by the goblet cells protects the gastrointestinal tract’s lining from the detrimental effects of the stomach’s acid.

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Transportation

Simple columnar epithelium lines the ducts of various glands, such as the gallbladder, which aids in the flow of hormones and enzymes to their sites of action.
Similarly, the cilia in the respiratory tract’s columnar epithelium beat in unison to move mucus and foreign particles into the throat, where they can be coughed up and swallowed or spit out.
The female reproductive system’s columnar epithelium contains cilia, which aid in the movement of oocytes discharged from the ovaries through uterine (fallopian) tubes into the uterus.

Simple Columnar Epithelium: Location and Examples

The simple columnar epithelium is mostly found in areas that perform secretion and absorption functions.
In the respiratory system, the ciliated columnar epithelium lines some bronchioles (small tubes), while in the reproductive system, it lines the uterine (fallopian) tubes and uterus.
Similarly, the columnar epithelium lines some paranasal sinuses, the spinal cord’s central canal, and the brain’s ventricles.
The gastrointestinal tract, as well as gland ducts and the gallbladder, are lined by non-ciliated columnar epithelium.
Some sections of the kidney (collecting ducts) are lined with simple columnar epithelium.

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Simple Columnar 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.
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