Transitional Epithelium | Introduction, Types & Function

By | November 15, 2019

Transitional Epithelium

Transitional Epithelium Definition:

What is Transitional epithelium: It is defined as a stratified tissue composed of multiple cell layers, where cells constitute the tissue may change shape on the basis of distention on the organ. When an organ filled with fluid, the cells present on the topmost layer of the transitional epithelium may stretch and look flattened, while they may also look cuboidal with the round shape when low pressure occurs of fluid.

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The transitional epithelium present inlining the urinary bladder, ureters, and urethra, as well as found in ducts of the prostate gland.

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The function of Transitional Epithelium:

One of the main functions of transitional epithelium is to be an extremely effective permeability barrier for impenetrable to water and many small molecules, because of its location in the excretory system, especially in ureters and urinary bladder. The cells of this epithelium are among the more resistant to osmotic pressure.

The second main function of these epithelium tissues is to permit the organs to stretch and increase the volume on the basis of fluid pressure. The cells in the superficial layer of this epithelium are able to change in shape that permits these organs to stretch without exposing underlying tissue to toxic substances in the urine

Structure of Transitional Epithelium:

The transitional epithelium is composed of 3-4 layers of cells in which the lowermost or basal layer stays in contact with the basement membrane. The cells on the basal layer are attached with lamina propria by tonofilaments and Hemi desmosomes. The cells in intermediate layers are proliferative and may replenish cells lost because of abrasion or infection. They also contain a vast Golgi network that has a number of membrane-bound vesicles. The superficial layer of cells can be changed from cuboidal in order to appear flattened when organ distend and have a number of actin-based cytoplasmic projections called microvilli.

All cells of transitional epithelium are deeply connected with each other by the junctional complexes. These junctional complexes are the symmetrical attachment of two cells that are usually composed of three components; a band of tight junctions on the apical surface followed by an intermediate series of adherents and located on desmosomes.

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Examples of Transitional Epithelium:

The transitional epithelium was commonly present in urinary and in the male reproductive tract in humans. These are the areas where volume and osmolarity of the organ can be changed fastly.

In the urinary system, the volume and concentration of solutes in urine are depending on a number of factors. The prostatic urethra in the male reproductive system is lined with transitional epithelium which continues with the epithelium of bladder. It is a much dilatable part of the urethra which expands and contracts on the basis of the flow of urine or semen.

  • Bladder:

A bladder is an organ that is designed in order to hold a large proportion of toxic body, liquid waste as before it expels from the body. When it distended completely, the urinary bladder can carry about 500ml of urine, makes it an organ that has a drastic change in volume over a short time period. Three layers of muscle fibers contribute toward the distention and contraction of the organ occurs.

The junctional complexes and plaques the superficial cells secure the body from the effects of storing urea, ammonia and many other metabolites in the bladder. The plaques also used to help apical cells which adjust the surface area of their plasma membrane.

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