Information

Binucleate cells of transitional epithelium (bladder)?


Working through Histology slides of the transitional epithelium (urothelium) of the urinary bladder, I noticed that the dome-shaped cells at the top of the transitional epithelium are frequently binucleate. In doing research, I found that the top cells of the transitional epithelium are 'often binucleate and usually polyploid'

Why is this? What purpose does this serve?
Is the binucleate feature consistent enough across slides to be used as a common identifying feature to recognise transitional epithelium from the urinary tract? Is the absence/over-abundance of binucleate cells characteristic of certain diseases?

I also see prominent granules (of glycogen, I presume?) in these cells.

Is this glycogen? & What purpose does this serve?

Also, I'm having difficulties recognising transitional epithelium in slides. Does anyone have any tips to share on how to easily recognise transitional epithelium as such (common features to look out for, etc.), especially in distinction to pseudo-stratified epithelium, which often looks similar?


In other stratified epithelium, it is the basal cells that replicate to replace the cells lost in the top layers. In transitional epithelium, which is also a stratified epithelium, the most superficial layer of cells are replaced or turnover occurs because of mitosis of the superficial facet cells themselves. In this case it is not unusual to see dividing cells in its last stage of division as a large cell containing two nuclei, which soon that cell will be 2 cells.


The appearance of transitional epithelium differs according to its cell layer. Cells of the basal layer are cuboidal (cube-shaped), or columnar (column-shaped), while the cells of the superficial layer vary in appearance depending on the degree of distension. [1] These cells appear to be cuboidal with a domed apex when the organ or the tube in which they reside is not stretched. When the organ or tube is stretched (such as when the bladder is filled with urine), the tissue compresses and the cells become stretched. When this happens, the cells flatten, and they appear to be squamous and irregular.

Cell layers Edit

Transitional epithelium is made up of three types of cell layers: basal, intermediate, and superficial. [2] The basal layer fosters the epithelial stem cells in order to provide constant renewal of the epithelium. [3] These cells' cytoplasm is rich in tonofilaments and mitochondria however, they contain few rough endoplasmic reticulum. The tonofilaments play a role in the attachment of the basal layer to the basement membrane via desmosomes. [4] The intermediate cell layer is highly proliferative and, therefore, provides for rapid cell regeneration in response to injury or infection of the organ or tube in which it resides. [3] These cells contain a prominent Golgi apparatus and an array of membrane-bound vesicles. [4] These function in the packaging and transport of proteins, such as keratin, to the superficial cell layer. The cells of the superficial cell layer that lines the lumen are known as facet cells or umbrella cells. This layer is the only fully differentiated layer of the epithelium. It provides an impenetrable barrier between the lumen and the bloodstream, so as not to allow the bloodstream to reabsorb harmful wastes or pathogens. [3] All transitional epithelial cells are covered in microvilli and a fibrillar mucous coat. [2]

The epithelium contains many intimate and delicate connections to neural and connective tissue. These connections allow for communication to tell the cells to expand or contract. The superficial layer of transitional epithelium is connected to the basal layer via cellular projections, such as intermediate filaments protruding from the cellular membrane. These structural elements cause the epithelium to allow distension however, these also cause the tissue to be relatively fragile and, therefore, difficult to study. All cells touch the basement membrane. [ citation needed ]

Cell membrane Edit

Because of its importance in acting as an osmotic barrier between the contents of the urinary tract and the surrounding organs and tissues, transitional epithelium is relatively impermeable to water and salts. This impermeability is due to a highly keratinized cellular membrane synthesized in the Golgi apparatus. [5] The membrane is made up of a hexagonal lattice put together in the Golgi apparatus and implanted into the surface of the cell by reverse pinocytosis, a type of exocytosis. [6] The cells in the superficial layer of the transitional epithelium are highly differentiated, allowing for maintenance of this barrier membrane. [6] The basal layer of the epithelium is much less differentiated however, it does act as a replacement source for more superficial layer. [6] While the Golgi complex is much less prominent in the cells of the basal layer, these cells are rich in cytoplasmic proteins that bundle together to form tonofibrils. These tonofibrils converge at hemidesmosomes to attach the cells at the basement membrane. [4]

The transitional epithelium cells stretch readily in order to accommodate fluctuation of volume of the liquid in an organ (the distal part of the urethra becomes non-keratinized stratified squamous epithelium in females the part that lines the bottom of the tissue is called the basement membrane). Transitional epithelium also functions as a barrier between the lumen, or inside hollow space of the tract that it lines and the bloodstream. To help achieve this, the cells of transitional epithelium are connected by tight junctions, or virtually impenetrable junctions that seal together to the cellular membranes of neighboring cells. This barrier prevents re-absorption of toxic wastes and pathogens by the bloodstream.

Urothelium is susceptible to carcinoma. Because the bladder is in contact with urine for extended periods, chemicals that become concentrated in the urine can cause bladder cancer. For example, cigarette smoking leads to the concentration of carcinogens in the urine and is a leading cause of bladder cancer. Aristolochic acid, a compound found in plants of the family Aristolochiaceae, also causes DNA mutations and is a cause of liver, urothelial and bladder cancers. [7] Occupational exposure to certain chemicals is also a risk factor for bladder cancer. This can include aromatic amines (aniline dye), polycyclic aromatic hydrocarbons, and diesel engine exhaust. [8]

Carcinoma Edit

Carcinoma is a type of cancer that occurs in epithelial cells. Transitional cell carcinoma is the leading type of bladder cancer, occurring in 9 out of 10 cases. [9] It is also the leading cause of cancer of the ureter, urethra, and urachus, and the second leading cause of cancer of the kidney. Transitional cell carcinoma can develop in two different ways. Should the transitional cell carcinoma grow toward the inner surface of the bladder via finger-like projections, it is known as papillary carcinoma. Otherwise, it is known as flat carcinoma. [9] Either form can transition from non-invasive to invasive by spreading into the muscle layers of the bladder. Transitional cell carcinoma is commonly multifocal, more than one tumor occurring at the time of diagnosis.

Transitional cell carcinoma can metastasize, or spread to other parts of the body via the surrounding tissues, the lymph system, and the bloodstream. It can spread to the tissues and fat surrounding the kidney, the fat surrounding the ureter, or, more progressively, lymph nodes and other organs, including bone. Common risk factors of transitional cell carcinoma include long-term misuse of pain medication, smoking, and exposure to chemicals used in the making of leather, plastic, textiles, and rubber. [10]


Bladder Cancer Stem Cells

Author(s): Mai N. Tran, Goodwin Jinesh G., David J. McConkey, Ashish M. Kamat Department of Urology, Unit 1373, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.

Affiliation:

Journal Name: Current Stem Cell Research & Therapy

Volume 5 , Issue 4 , 2010




Abstract:

Stem cells are undifferentiated cells that renew themselves while simultaneously producing differentiated tissue- or organspecific cells through asymmetric cell division. The appreciation of the importance of stem cells in normal tissue biology has prompted the idea that cancers may also develop from a progenitor pool (the “cancer stem cell (CSC) hypothesis”), and this idea is gaining increasing acceptance among scientists. CSCs are sub-populations of cancer cells responsible for tumor initiation, differentiation, recurrence, metastasis, and drug resistance. First identified in the hematopoietic system, CSCs have also been discovered in solid tumors of the breast, colon, pancreas, and brain. Recently, the tissue-specific stem cells of the normal urothelium have been proposed to reside in the basal layer, and investigators have isolated phenotypically similar populations of cells from urothelial cancer cell lines and primary tumors. Herein, we review the CSC hypothesis and apply it to explain the development of the two different types of bladder cancer: noninvasive (“superficial”) carcinoma and invasive carcinoma. We also examine potential approaches to identify CSCs in bladder cancer as well as therapeutic applications of these findings. While exciting, the verification of the existence of CSCs in bladder cancer raises several new questions. Herein, we identify and answer some of these questions to help readers better understand bladder cancer development and identify reasonable therapeutic strategy for targeting stem cells.

Current Stem Cell Research & Therapy

Title: Bladder Cancer Stem Cells

VOLUME: 5 ISSUE: 4

Author(s):Mai N. Tran, Goodwin Jinesh G., David J. McConkey and Ashish M. Kamat

Affiliation:Department of Urology, Unit 1373, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.

Abstract: Stem cells are undifferentiated cells that renew themselves while simultaneously producing differentiated tissue- or organspecific cells through asymmetric cell division. The appreciation of the importance of stem cells in normal tissue biology has prompted the idea that cancers may also develop from a progenitor pool (the “cancer stem cell (CSC) hypothesis”), and this idea is gaining increasing acceptance among scientists. CSCs are sub-populations of cancer cells responsible for tumor initiation, differentiation, recurrence, metastasis, and drug resistance. First identified in the hematopoietic system, CSCs have also been discovered in solid tumors of the breast, colon, pancreas, and brain. Recently, the tissue-specific stem cells of the normal urothelium have been proposed to reside in the basal layer, and investigators have isolated phenotypically similar populations of cells from urothelial cancer cell lines and primary tumors. Herein, we review the CSC hypothesis and apply it to explain the development of the two different types of bladder cancer: noninvasive (“superficial”) carcinoma and invasive carcinoma. We also examine potential approaches to identify CSCs in bladder cancer as well as therapeutic applications of these findings. While exciting, the verification of the existence of CSCs in bladder cancer raises several new questions. Herein, we identify and answer some of these questions to help readers better understand bladder cancer development and identify reasonable therapeutic strategy for targeting stem cells.


What Is the Function of Transitional Epithelium Cells?

The function of transitional epithelium cells is to protect the urinary system against the toxic effects of urine. Additionally, transitional epithelium cells stretch to accommodate the volume of the bladder and other organs when they fill with liquid.

According to McGraw-Hill, transitional epithelium cells line the ureters, urethra and bladder. These cells begin at the pelvis and continue through the kidneys to the ureters and the bladder. These cells are necessary because as the volume and pressure within these urinary organs build, the organs need to stretch. According to Austin Community College, stretching helps the organs lined with transitional epithelium cells change their shape without damaging the epithelial lining.

When the transitional cells are in their normal state, the cells appear to be round and ovoid. However, when they stretch, the cells become flat. To accommodate the stretching and pulling of the urinary system, transitional epithelium cells are stratified, which means in layered.

Because the transitional cells are in layers, it also means sometimes these transitional cells slough off into the urine, much the same way that dead skin cells flake off. According to Cornell University, this occurs in low numbers because transitional cells are intended to protect the urinary tract from the damaging effects of urine. If a large amount of transitional epithelium cells is found in the urine, however, it is a sign of a dysfunction. In healthy adults, only a few transitional epithelial cells are typically found in urine.


Urinary Tract Epithelial Cells Cultured from Human Urine

The behavior of cultured normal human epithelial cells is of particular importance to the interrelated studies of differentiation, senescence, and carcinogenesis. Epithelial cultures that either retain differentiated cellular functions in vitro or develop differentiated characteristics upon proliferation of stem cells help to relate the division potential of different cell types in vivo to limits on divisions in vitro. An epithelium consists of cells that are closely applied to each other with no intervening fibrous material. Epithelial cells are found on the outer body surface, on the surfaces of body tubes and cavities, and as functional units of glands. This chapter presents the preliminary results in developing a standard culture method for cells derived from urine. Urine cell cultures are purely epithelial without the use of enrichment or selective procedures for removing contaminating fibroblasts. These cultured epithelial cells form rapidly dividing populations that can be cloned or maintained as a mass culture through several passages, although the urine cells undergo fewer population doublings than the fibroblasts.


Types of epithelial cells in urine and their meaning

In general, a low number of epithelial cells is of no importance but if they are in high quantity it is important to determine what type they are and their concentration . In the urine, three types of epithelial cells can be found: squamous or flat, transitional and tubular cells of the renal epithelium.

Squamous Cells

Also called flat cells due to their shape, they are thin cells coming mainly from the vaginal epithelium or the distal urethral epithelium and are common in the urine in low quantity. A high content in squamous epithelial cells is indicative of a possible vaginitis or urethritis . This type of cells is also found in the epithelium of the genitals outside the body, so that their presence in high numbers may be due to contamination or incorrect collection of the sample.

When a high number of squamous cells is found in urine, a new sample is usually requested to compare the results with emphasis on collection rules and instructions that minimize the risk of contamination.

Transitional cells

They come from the epithelium that covers the proximal urethra and the bladder. It is associated with inflammatory processes , usually related to infections . A high number of transitional cells are also observed in patients with renal lithiasis .

Renal tubular cells

They are the cells that cover the renal tubules (part of the nephron) and in normal conditions do not appear in urine . Its presence is related to kidney damage such as acute tubular necrosis, some viral diseases (such as cytomegalovirus nephritis), pyelonephritis, rejection of transplants and toxic reactions to certain substances. Those known as fatty oval bodies are these same lipid-laden cells that appear in the nephritic syndrome .

When tubular cells appear in the urine, it is common for more tests to be ordered and a renal profile is done to find out what is happening in the kidney and to be able to give a specific differential diagnosis.


Discussion

Our study provides evidence that episodes of E. coli cystitis in humans may involve an IBC pathogenic pathway similar to that observed in mice. Evidence of filamentous bacteria and exfoliated bladder facet cells containing large collections of E. coli were observed by light microscopy and confirmed by immunofluorescence. High-resolution electron microscopy showed large biofilm-like IBCs and long filamentous bacteria. The expected variety of uropathogens [6] was cultured from infected women in the study, yet IBCs and filaments were not observed in urines from women infected with gram-positive pathogens or in urines from asymptomatic women. Additionally, the urine cytologies observed in human and murine UTIs were indistinguishable.

Previous studies support our findings of an intracellular bacterial niche during UTI. In one study, human bladder biopsies from 33 women with recurrent urinary tract symptoms were analyzed after antibiotic therapy [22]. Sixteen of these patients had sterile urine cultures however, bacteria were cultured from 8 patients' biopsies. These findings suggest that urine culture results may not necessarily reflect the true bacteriologic status of the bladder epithelium and that there may be a persistent niche for uropathogens associated with bladder tissue. In addition, multiple studies have shown that UPEC strains are able to invade and replicate within human urothelial cell lines [15,16,23]. More recently, it was demonstrated that the majority of UPEC isolates from patients with various clinical syndromes of UTI are competent for IBC formation in the murine cystitis model [24].

The ability to form filaments is an important virulence property that facilitates persistence in the murine cystitis model [25]. Filamentation can be the result of the gram-negative bacterial SOS response, which is induced by a variety of stressful stimuli, including antibiotics [26]. In this study, however, patients had no recent history of antibiotic usage. Also, filamentation did not correlate with WBC counts in the urines of these patients, as one might expect if this were a nonspecific stress response. Thus, the filaments likely represented bacteria that had emerged from an intracellular niche as seen in the murine model. The filamentation event has been shown to be triggered by TLR-4-dependent inflammatory responses in the murine model of cystitis [25], however, whether this is also true in the human remains to be determined. We were able to capture electron microscope images of these filamentous bacteria within the intracellular niche of sloughed urothelial cells. In addition, the urine finding of filamentous bacteria significantly correlated with the presence of IBCs in these samples. This correlation could be explained by the association of these two entities in the same pathogenic pathway or may be due to the higher bacterial burden in these samples and an enhanced ability to detect these endpoints by microscopy.

Interestingly, the presence of IBCs or filaments was associated with patients who had significantly longer self-reported durations of symptoms. This finding may relate to the kinetics of the IBC cycle and the time point at which IBCs are exfoliated into the urine, or it may be related to the higher burden of bacteria in the urines at these time points. Each urine analyzed represents a single point in what may be a temporally regulated pathogenic pathway. IBCs and filaments are likely transient [14] and, thus, could be missed if the sampling interval is not appropriate. In addition, the volume of urine analyzed represents a small proportion of the total sample micturated. Thus, the findings in this study may underestimate the prevalence of the IBC pathway.

Exfoliated cells found in the urine, while a useful reflection of the bladder tissue, have generally lost considerable structural integrity. Bacterial invasion into these damaged cells after they have been shed from the urothelium, while possible, seems unlikely. Mistaking such rare events for IBCs is implausible because samples were fixed upon micturition and bacteria would have needed significant time to multiply into large biofilm-like communities. While bladder biopsies are usually contraindicated in actively infected patients, future studies could assess biopsies from selected women with a history of recurrent UTI for the presence of an intracellular reservoir. As is observed in the murine model [15,19,20], a quiescent intracellular bacterial reservoir forms within the transitional epithelium. In this model, epithelial turnover and differentiation induce the bacteria within this reservoir to emerge and initiate the formation of new IBCs and recurrent bacteriuria. Reservoir formation, not explored in this study, could possibly serve as a seed for recurrence in same-strain UTIs in some women.

This study involved a large number of well-characterized young healthy women with acute cystitis and provides strong evidence that IBCs and filamentous bacteria can be found in this group of women. However, there are also several limitations to this study. We cannot extrapolate our results to women with different demographic characteristics or with different clinical syndromes, such as asymptomatic bacteriuria, pyelonephritis, or catheter-associated infections. We were not able, because of treatment considerations, to collect serial specimens from these women with acute cystitis, and thus we could not optimize collection time points when IBCs and filaments might be most abundant. The patients were not followed prospectively and thus we cannot evaluate important temporal associations between presence of IBCs or filaments and response to treatment and patterns of recurrence. It is possible that the sensitivity of our assays might have been better if we had been able to analyze urines quickly without the agitation of shipping. The low number of non- E. coli infections makes it difficult to assess the ability of other uropathogens to form filaments and IBCs during human infection. Lastly, it was outside the scope of this study to perform genetic analyses of bacteria collected, as has been done in previous studies [24,27]. Thus, potential genetic differences and other characteristics of bacteria collected in this study are not known at this time.

Despite these limitations, our data provide compelling evidence that there is an association between IBCs, filaments, and acute uncomplicated cystitis in young women and are suggestive of an IBC pathway in a subset of these women. In this pathway in mice, bacteria are able to invade and replicate within the urothelium where they are largely protected from host innate immunity, which may explain how the relatively few bacteria introduced into the bladder with urethral milking or sexual intercourse [28–30] are able to survive and multiply to numbers high enough to elicit symptoms in the host. The implications of these observations with regard to clinical management remain unclear. Urine IBCs and filaments may be prognostic indicators of specific clinical outcomes, or women with these findings may benefit from different management or prevention strategies such as longer treatment or use of antimicrobials with better intracellular penetration. It is imperative that additional studies with appropriate patient follow-up be conducted to address these specific questions. Further understanding of the IBC pathogenic pathway in human infection may provide new potential targets and approaches to the treatment and prevention of UTI.


Epithelial Cells in Urine

Epithelial cells help protect or enclose organs, according to an article in Medlineplus.com. They are found in the ureters, bladder and urethra they are round or oval depending on the location such as renal pelvis and the bladder. When stretched though, they can appear flat.

These cells can appear in urine. High epithelial cells may cause concern because this can be an indication of inflammation, infections and even malignancies. Bladder infection can be a result of large amount of epithelial cells in the urine.

There are four main types of epithelial cells seen in urine. They also differ in ways such as larger size, smaller nuclei and irregular border or cells.

Renal tubular epithelial cells

This type is not common in urine. In contrast to the transitional epithelium, these cells are smaller and rounder. When a large growing statistics of cells set up in urine, it may be an indication of a kidney problem.

Neoplasia cells

TCC or transitional cell carcinoma, may bog the cells into the urine and can lead to hemorrhage while invading the bladder wall in most time.

Epithelial Cells in Urine Normal Range

The range: “few,” “moderate,” or “many” – per LPF. The normal range is less than 15-20 cells per HPF.

Other Substances in Urine Meaning

There are other substances that present in your urine sample.

Red Blood Cells (RBCs)

If RBCs found in urine, it indicates some health problems including inflammation in urinary tract or kidney disease. Otherwise, it can be just an indication of unclear urine sample or blood from menstruation or hemorrhoids. You may do the test twice.

White Blood Cells (WBCs)

If the amount of WBCs is high, it can indicate an infection in urinary tract.

Microorganisms

A urinary tract infection can cause bacteria into your urine sample. If yeast is in urine for women, then it is yeast infection.

It’s abnormal if there are crystals like cysteine or leucine found in urine, kidney stone is a possibility although it can also be due to xray and some medications.

Red blood cell casts will indicate a glomeruli hitch and white blood cell casts will specify a kidney inflammation.


Introduction

Normal urothelium serves as the main source of a major class of soluble, urine proteins including urokinase, tissue-type plasminogen activator, and a potent serine protease inhibitor, PP5 [1] their synthesis requires differentiation of the vesical urothelium. It is speculated that these urinary proteins and their inhibitors play a crucial role in regulating desquamation of urothelium, which constitutes a vital defence mechanism against bacterial attachment. Thus the mammalian urothelium, besides acting as a permeability barrier, may serve important functions in prevention of bacterial cystitis.

Urothelium is characterised by terminally differentiated superficial cells ("umbrella cells"), that express uroplakins in their luminal plasma membrane and cytokeratin 20 in their cytoplasm. Basal and intermediate cells are cytokeratin 20 negative. [2] In contrast to normal urothelium, cultured human stratified urothelium does not undergo complete terminal differentiation of its superficial cells. Using immunohistochemical staining with specific antibodies, the superficial layer of reconstructed stratified urothelium has been shown to express uroplakins but not cytokeratin 20 [3–5].

We studied cytokeratin-20 immunostaining of bladder biopsies taken from spinal cord injury patients. It is possible that injury to the spinal cord, and consequent lack of trophic effect upon the urothelium, may lead to incomplete maturation and differentiation. [6]. As normal urothelium is characterised by cytoplasmic cytokeratin 20 expression in terminally differentiated superficial cells, cytokeratin 20 was taken as a marker of complete terminal differentiation of urothelial cells in bladder biopsies. If spinal cord injury does indeed affect urothelial differentiation or induces squamous or other metaplastic change undetected by histological analysis, the superficial urothelial cells in the neuropathic bladder of SCI patients may not show positive immunostaining for cytokeratin 20.


Types of Epithelial Tissue

Epithelial tissues are classified into several categories on the basis of the cell shape and number of cell layers. Mainly there have the fallowing three types of epithelial tissue:
1) Simple epithelium
2) Compound epithelium
3) Transitional epithelium

Simple epithelium as one of the types of Epithelial Tissue

Simple epithelium consists of a single layer of cells resting upon a basement membrane. It occurs mainly on secretory and absorptive surfaces and seldom covers surfaces exposed to mechanical or chemical abrasions since it cannot effectively protect underlying tissues. The following five types of simple epithelia are acknowledged on the basis of the shape and structure of component cells.

Squamous epithelium

This types of Epithelial Tissue consists of a layer of thin, flat, scale-like cells with prominent nuclei. These cells are closely fitted together like the tiles in a floor. Inter-digitations and other junctions between adjacent cells keep the epithelium intact as a sheet. This epithelium easily exchange materials by diffusion across it.

Cuboidal Epithelium

The cuboidal epithelium consists of cells which appear cuboidal in vertical section. These cells possess usually rounded nuclei, and participate in secretion, excretion and .absorption. Cuboidal epithelium forms the lining of salivary and pancreatic ducts and thyroid vesicles, and so also of ciliary body, choroid and iris of eye.

Columnar epithelium

The cells of columnar epithelium appear rectangular in vertical section and polygonal in surface view. In keeping with the shape of the cell, the nuclei are also frequently elongated. The surface of the columnar epithelium is sometimes covered with microvilli, which are arranged regularly or irregularly. The cells of the columnar epithelium have a secretory or absorptive function. Secretory columnar cells are scattered in the mucosa of the stomach and intestine.

Ciliated epithelium

These types of Epithelial Tissue which called Ciliated epithelium consists of columnar or cubical cells bearing cilia on their free surfaces. The function of the cilia is to move particles or mucus in a specific direction over the epithelial surface. Ciliated columnar epithelium lines most of the respiratory tract, uterus, and uterine tubes. It is also found in the efferent duct of testis, parts of the middle ear and auditory tube, and in the lining of neurocoel cavity of the spinal cord and brain.

Pseudo-stratified epithelium

These types of Epithelial Tissue are invariably made up of a single layer of columnar cells. But it appears more than one cell layer as some cells are shorter than the others and their nuclei are present at different levels. Some cells are broader near the base, whereas others near the apex. As the nuclei occur in the broader part of the cell, they do not form a layer. To distinguish it from a true stratified epithelium, it is called pseudo-stratified epithelium.

Compound epithelium as one of the types of Epithelial Tissue

Compound epithelium consists of more than one layer of cells. The cells of the innermost layer rest on the basement membrane. Being multi-layered, compound epithelium has little role in secretion or absorption, but it provides protection to underlying tissues against mechanical, chemical, thermal or osmotic stress. The following two types of compound epithelium have been acknowledged.

Stratified epithelium

It consists of many layers of epithelial cells the innermost layer consists of cuboidal cells. On the basis of the morphology of superficial layers, the stratified epithelium is divided into two sub-types.
i) Stratified squamous epithelium: It consists of several superficial layers of living squamous cells and deeper layers of interlinked polygonal cells. Most of the stratified epithelium in the adult body is of this type and these cells contain a highly insoluble fibrous protein, called keratin, which forms a non-living covering over the epithelium.
ii) Stratified cubical epithelium: In these types of epithelial tissue, the superficial cells are cuboidal. The conjunctiva of eyes and the lining of the ducts of sweat glands, female urethra and some parts of the anal canal have this type of epithelium.

Transitional epithelium as one of the types of Epithelial Tissue

Transitional epithelium is comparatively thin and more stretchable than stratified epithelium. It is 4-6 cell layers thick with extensive inter-digitations. The innermost layer consists of columnar or cuboidal cells, the 2 or 3 middle layers are made up of polyhedral or pear-shaped cells, and the surface layer has large, broad, rectangular or oval cells. Transitional epithelium occurs in the renal pelvis, ureter, urinary bladder and part of the urethra.


Watch the video: PSEUDOSTRATIFIED COLUMNAR EPITHELIA (December 2021).