Cuboidal Epithelium - Types and Functions

What are Epithelial Cells?

Epithelium or epithelial cells are specialised cells that perform specific functions. It is typically a continuous and thin layer of compactly packed cells with a very little intercellular matrix. The epithelial cells can be secretory (glandular epithelia) or lining epithelia. It is more of a discretional functional grouping as there are lining epithelia that also have secretory cells (e.g., the lining of the stomach). Also, there are glandular cells that are dispersed among the lining cells (e.g., mucous cells in the trachea and small intestine).

Types of Epithelial Cells

Based on the total cell layers, epithelia can be classified into –

• Simple epithelium – comprise a single cell layer
• Stratified epithelium – comprises two or more cell layers

Based on the cell shape, the simple and stratified can be further divided into –

• Squamous – cells are flat and thin
• Cuboidal – cells with roughly similar thickness and width
• Columnar – cells are taller than wide

Explore: Epithelial Tissue and Connective Tissue

Cuboidal Epithelium

Cuboidal epithelial cells are short cells with roughly similar thickness and width. They usually appear hexagonal in a cross-section. The simple cuboidal epithelia are more common than the stratified cuboidal epithelia. A few cuboidal epithelial cells located in different parts are discussed here –

• The intercalated ducts (a portion of the exocrine gland) has the thinnest epithelium that is typically distinguished as “low” simple cuboidal.
• The bile canals of Hering are partially lined by hepatocytes and cholangiocytes. Cholangiocytes are the simple cuboidal epithelial cells of the bile duct. Furthermore, they contribute to bile secretion.
• Terminal bronchioles also have the simple cuboidal epithelium that contains club cells that are non-ciliated and have dome-shaped apical ends with secretory granules. They have innate immunity and surfactant secretory functions. Club cells are usually either low cuboidal or low columnar in nature.
• They are also located in the renal tubules, especially in the proximal convoluted tubule, distal convoluted tubule, thick ascending limb and also in the collecting ducts.

Simple Cuboidal Epithelium

The cells of simple cuboidal epithelium are almost tall as they are wide. They contain a single layer of cuboidal cells with large spherical nuclei that are centrally located. Their major functions are absorption and secretion. Moreover, their prominent thickness permits cytoplasm to be rich in mitochondria and also other organelles for a high degree of active transport across the epithelium and other functions. Examples – cells covering thyroid follicles, ovary, etc.

The simple cuboidal epithelium also lines the pigment layer of the retina.

Stratified Cuboidal Epithelium

Stratified cuboidal as well as stratified columnar are rare occurrences. Stratified cuboidal epithelium occurs in the excretory ducts of sweat glands and salivary glands. They are also found in mammary glands and in the developing ovarian follicles.

Cuboidal Epithelium Function

The major functions of cuboidal epithelial cells are – protection, secretion and absorption.

Some cuboidal epithelial cells have specialised structures (like microvilli or cilia) projecting from the cells. These structures function either to increase the apical surface area for better absorption or move substances along the epithelial surface. E.g. the ​​proximal convoluted tubule of the kidneys has microvilli.

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