Transitional epithelium Definition, Structure, Function, Location, and Example

What is transitional epithelium?

The epithelium of transition is a form of stratified epithelium that comprises several layers of cells, where their shape cells changes in accordance with the function that the organ performs. The epithelium can have a varied appearance, as it appears to be circular or cubic in a relaxed state with the exception of the apical layer that appears flat when stretched. The epithelium is essentially restricted to the urinary system that’s why it’s sometimes referred to”urothelium” “urothelium”.

Structure of the transitional epithelium

  • Epithelial tissue that in a relaxed state , appears as a cuboidal epithelium that is stratified.
  • The cells of the epithelium transitional are round or pear-shaped, but when tissues are stretched, they get flattened, resulting in the appearance of a stratified epithelium.
  • The cells of the base layer look to be cuboidal or columnar, whereas the cells of the apical layer appear flat according to the extent of extension.
  • The layers of cells within the epithelium are separated into three distinct groups.
  • The lowest layer is known as the basal layer that is directly connected with the basement membrane. The basement Membrane is accountable for an ongoing renewal of cells in the upper layers.
  • The cells of the basal layer are enriched of cytoplasmic proteins that join together to form tonofibrils. These connect with hemidesmosomes and create a strong connection to the basement membrane.
  • The cells of the base layer are wealthy in mitochondria, as they need more power to support the renewal of epithelium.
  • In the middle, also also known as”the intermediate layer,” is comprised of proliferative and rapidly dividing cells which provide rapid growth in cases of damage or injury to cells already present.
  • The cells of this layer are plentiful within the Golgi apparatus, which aids in the movement of proteins, such as Keratin, to the layers below.
  • Cells of the outer layer are highly keratinized that creates a barrier against the effects of water and salts.
  • The apical layer, also known as”the superficial layer”, forms the lumen and shields the cell’s underlying layer against pathogens that cause harm to the cells within the lumen.
  • A few cells within the layer that is superficial are covered by microvilli, and are surrounded with a mucus coat.
  • The epithelium’s cells are linked through gap junctions and desmosomes. These structural elements permit the epithelium’s size to grow but also causes cells to weaken.
  • As with all epithelial tissues that are present, the epithelium of transition is also avascular and has no blood vessels. The epithelium’s cells depend on the blood vessels in the adjacent connective tissues to supply oxygen, nutrients and excretion.
  • But, they do possess an individual nerve supply.

Transitional epithelium Functions

Based on the cell’s structure and its composition The transitional epithelium serves two major functions. They include:

Permeability barrier

Because of the huge amounts of keratin within cell walls, tissue has an excellent resistance to water, as well as other molecules. The tissues’ cells are extremely resistant to the pressure of osmotic, which stops dehydration even when cells are completely stretched. Chemicals and toxins are also prevented from entering the bloodstream. An excellent example of this is in the urinary tract, where , even if hypertonic urine is in the lumen, cells in the urothelium have not dehydrated.

Volume control

Another significant role of the epithelium its ability to permit organs to alter their shape and expand in size by stretching when the pressure of the fluid rises. Within the excretory organs when the volume of urine in the bladder and ureters rises and the cells of the outer layer stretch, changing their shape from flat to round. The stretching expands the size of the organs, while also protecting the tissue beneath it from contact with the toxic substances present in the urine.

Transitional epithelium location and Example

  • The most well-known epithelium that is transitional can be seen in the urothelium.
  • The urothelium or epithelium of transition lines your urinary bladder ureters and a portion of the urethra.
  • In the same way, the prostatic urethra’s membrane within the reproductive tract of males is lined by the epithelium transitional that is a part of the urothelium that lines your urinary bladder.


It is an organ specifically designed to hold a substantial portion of the body’s hazardous liquid waste prior to its removal out of the body. When full the bladder could hold up to 500 milliliters of urine. This makes it an organ that experiences dramatic variations in its volume in brief periods of time. Three layers of muscles are responsible for the expansion and dilation of the organ The transitional epithelium is also essential. The junctional complexes and the uroplakin plaques in the cells of the surface shield the body from the consequences of storing ammonia, urea and various metabolites within the bladder. Furthermore these plaques are believed to aid apical cells to adjust the size that their plasma membranes have. For instance when the bladder becomes dilapidated there is an increase in membrane size which could be due to an fusion process of the vesicles within and within the Golgi network.

Transitional epithelium Definition, Structure, Function, Location, and Example

Image shows a cross-section of a bladder’s wall with flattened superficial cell layers in the epithelium transitional. The submucosa, and 3 layers of muscles fibers.


Q1. where is transitional epithelium found?

Transitional epithelia are found in tissues such as the urinary bladder where there is a change in the shape of the cell due to stretching.

Q2. what is the value of transitional epithelium in the urinary system?

It allows distention. Put the portions of the male urethra in the correct order, from the urinary bladder to the exterior. Both the proximal convoluted tubule and the distal convoluted tubule reside in the cortex of the kidney.

Q3. what is the function of transitional epithelium?

The transitional epithelium of the urinary tract is lined by a layer of glycosaminoglycans (GAGs) that function to prevent microbial and crystal adherence to the bladder epithelium and minimize the movement of urine solutes and proteins through the bladder epithelium.

Q4. which organ system is lined by transitional epithelium to accommodate stretching?

The innermost layer of the bladder is the mucosa layer that lines the hollow lumen. Unlike the mucosa of other hollow organs, the urinary bladder is lined with transitional epithelial tissue that is able to stretch significantly to accommodate large volumes of urine.


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