Vaginal epithelium

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Vaginal epithelium
Gartner Duct Cyst (low power) (4881813679).jpg
The epithelium of the vagina, visible at top, consists of multiple layers of flat cells.
Details
Part of Vagina
Anatomical terminology

The vaginal epithelium is the inner lining of the vagina consisting of multiple layers of (squamous) cells. [1] [2] [3] The basal membrane provides the support for the first layer of the epithelium-the basal layer. The intermediate layers lie upon the basal layer, and the superficial layer is the outermost layer of the epithelium. [4] [5] Anatomists have described the epithelium as consisting of as many as 40 distinct layers of cells. [6] [7] The mucus found on the epithelium is secreted by the cervix and uterus. [8] The rugae of the epithelium create an involuted surface and result in a large surface area that covers 360 cm2. [9] This large surface area allows the trans-epithelial absorption of some medications via the vaginal route.

Contents

In the course of the reproductive cycle, the vaginal epithelium is subject to normal, cyclic changes, that are influenced by estrogen: with increasing circulating levels of the hormone, there is proliferation of epithelial cells along with an increase in the number of cell layers. [10] [11] As cells proliferate and mature, they undergo partial cornification. [9] [12] Although hormone induced changes occur in the other tissues and organs of the female reproductive system, the vaginal epithelium is more sensitive and its structure is an indicator of estrogen levels. [11] [12] [13] Some Langerhans cells and melanocytes are also present in the epithelium. [12] The epithelium of the ectocervix is contiguous with that of the vagina, possessing the same properties and function. [14] The vaginal epithelium is divided into layers of cells, including the basal cells, the parabasal cells, the superficial squamous flat cells, and the intermediate cells. [15] [16] [8] The superficial cells exfoliate continuously, and basal cells replace the superficial cells that die and slough off from the stratum corneum. [17] [18] [19] Under the stratus corneum is the stratum granulosum and stratum spinosum. [20] The cells of the vaginal epithelium retain a usually high level of glycogen compared to other epithelial tissue in the body. [21] The surface patterns on the cells themselves are circular and arranged in longitudinal rows. [7] The epithelial cells of the uterus possess some of the same characteristics of the vaginal epithelium. [22]

Structure

Vaginal epithelium forms transverse ridges or rugae that are most prominent in the lower third of the vagina. This structure of the epithelium results in an increased surface area that allows for stretching. [23] [24] [9] This layer of epithelium is protective, and its uppermost surface of cornified (dead) cells are unique in that they are permeable to microorganisms that are part of the vaginal flora. The lamina propria of connective tissue is under the epithelium. [4] [5]

Cells

cell typeFeaturesDiameterNucleiNotes
basal cell round to cylindrical, narrow basophilic cytoplasmic space12-14 μmdistinct, 8–10 μm in sizeonly in case of severe epithelial atrophy and in repair processes after inflammation
stratum granulosum part of the parabasal layer, round to longitudinal oval, cytoplasm basophilic20 μmclear cell nucleusFrequent glycogen storage, thickened cell margins and decentralized cell nucleus; Predominant cell type in menopausal women [12] [24] [16] [20]
stratum spinosum part of the parabasal layer [20] [16] [24]
intermediate cell oval to polygonal, cytoplasm basophilic30–50 μmapprox. 8 μm, decreasing core-plasma relation with increase in sizein pregnancy: barge-like with thickened cell margin ("navicular cells")
superficial squamous flat cells polygonal, baso- or eosinophilic, transparent, partially keratohyaline granule50–60 micronsvesicular and slightly stainable or shrunken [24] [16]
stratum corneumexfoliate, slough offbecome detached from the epithelium [18] [19] [17]

Basal cells

The basal layer of the epithelium is the most mitotically active and reproduces new cells. [18] This layer is composed of one layer of cuboidal cells lying on top of the basal membrane. [7]

Parabasal cells

The parabasal cells include the stratum granulosum and the stratum spinosum. [20] In these two layers, cells from the lower basal layer transition from active metabolic activity to death (apoptosis). In these mid-layers of the epithelia, the cells begin to lose their mitochondria and other cell organelles. [18] [25] The multiple layers of parabasal cells are polyhedral in shape with prominent nuclei. [7]

Intermediate cells

Intermediate cells make abundant glycogen and store it. [26] [27] Estrogen induces the intermediate and superficial cells to fill with glycogen. [19] [28] The intermediate cells contain nuclei and are larger than the parabasal cells and more flattened. Some have identified a transitional layer of cells above the intermediate layer. [7]

Superficial cells

Estrogen induces the intermediate and superficial cells to fill with glycogen. [19] [28] Several layers of superficial cells exist that consist of large, flattened cells with indistinct nuclei. The superficial cells are exfoliated continuously. [7]

Cell junctions

The junctions between epithelial cells regulate the passage of molecules, bacteria and viruses by functioning as a physical barrier. [14] [9] The three types of structural adhesions between epithelial cells are: tight junctions, adherens junctions, and desmosomes. "Tight junctions (zonula occludens) are composed of transmembrane proteins that make contact across the intercellular space and create a seal to restrict transmembrane proteins difusion. [17] of molecules across the epithelial sheet. Tight junctions also have an organizing role in epithelial polarization by limiting the mobility of membrane-bound molecules between the apical and basolateral domains of the plasma membrane of each epithelial cell. Adherens junctions (zonula adherens) connect bundles of actin filaments from cell to cell to form a continuous adhesion belt, usually just below the microfilaments." [14] Junction integrity changes as the cells move to the upper layers of the epidermis. [9]

Mucus

The vagina itself does not contain mucous glands. [29] [30] Though mucus is not produced by the vaginal epithelium, mucus originates from the cervix. [8] The cervical mucus that is located inside the vagina can be used to assess fertility in ovulating women. [29] The Bartholin's glands and Skene's glands located at the entrance of the vagina do produce mucus. [31]

Development

The epithelium of the vagina originates from three different precursors during embryonic and fetal development. These are the vaginal squamous epithelium of the lower vagina, the columnar epithelium of the endocervix, and the squamous epithelium of the upper vagina. The distinct origins of vaginal epithelium may impact the understanding of vaginal anomalies. [32] Vaginal adenosis is a vaginal anomaly traced to displacement of normal vaginal tissue by other reproductive tissue within the muscular layer and epithelium of the vaginal wall. This displaced tissue often contains glandular tissue and appears as a raised, red surface. [27]

Cyclic variations

During the luteal and follicular phases of the estrous cycle the structure of the vaginal epithelium varies. The number of cell layers vary during the days of the estrous cycle:

Day 10, 22 layers

Days 12-14, 46 layers

Day 19, 32 layers

Day 24, 24 layers

The glycogen levels in the cells is at its highest immediately before ovulation. [7]

Lytic cells

Different layers of the vaginal epithelium Vagina (mucosa).JPG
Different layers of the vaginal epithelium

Without estrogen, the vaginal epithelium is only a few layers thick. Only small round cells are seen that originate directly from the basal layer (basal cells) or the cell layers (parabasal cells) above it. The parabasal cells, which are slightly larger than the basal cells, form a five- to ten-layer cell layer. The parabasal cells can also differentiate into histiocytes or glandular cells. Estrogen also influences the changing ratios of nuclear constituents to cytoplasm. As a result of cell aging, cells with shrunken, seemingly foamy cell nuclei (intermediate cells) develop from the parabasal cells. These can be categorized by means of the nuclear-plasma relation into "upper" and "deep" intermediate cells. [11] Intermediate cells make abundant glycogen and store it. The further nuclear shrinkage and formation of mucopolysaccharides are distinct characteristics of superficial cells. The mucopolysaccharides form a keratin-like cell scaffold. Fully keratinized cells without a nucleus are called "floes". [33] [26] Intermediate and superficial cells are constantly exfoliated from the epithelium. The glycogen from these cells is converted to sugars and then fermented by the bacteria of the vaginal flora to lactic acid. [33] [28] The cells progress through the cell cycle and then decompose (cytolysis) within a week's time. Cytolysis occurs only in the presence of glycogen-containing cells, that is, when the epithelium is degraded to the upper intermediate cells and superficial cells. In this way, the cytoplasm is dissolved, while the cell nuclei remain. [33]

Epithelial microbiota

Glycogen is the complex form of sugar present in the vaginal epithelium that is metabolized into lactic acid Glycogen structure.svg
Glycogen is the complex form of sugar present in the vaginal epithelium that is metabolized into lactic acid

Low pH is necessary to control vaginal microbiota. Vaginal epithelial cells have a relatively high concentration of glycogen compared to other epithelial cells of the human body. The metabolism of this complex sugar by the lactobacillus dominated microbiome is responsible for vaginal acidity. [34] [35] [36]

Function

The cellular junctions of the vaginal epithelium help prevent pathogenic microorganisms from entering the body though some are still able to penetrate this barrier. Cells of the cervix and vaginal epithelium generate a mucous barrier (glycocalyx) in which immune cells reside. In addition, white blood cells provide additional immunity and are able to infiltrate and move through the vaginal epithelium. [14] The epithelium is permeable to antibodies, other immune system cells, and macromolecules. The permeability of epithelium thus provides access for these immune system components to prevent the passage of invading pathogens into deeper vaginal tissue. [9] The epithelium further provides a barrier to microbes by the synthesis of antimicrobial peptides (beta-defensins and cathelicidins) and immunoglobulins. [14] Terminally differentiated, superficial keratinocytes extrude the contents of lamellar bodies out of the cell to form a specialized, intercellular lipid envelope that encases the cells of the epidermis and provides a physical barrier to microorganisms. [9]

Clinical significance

Vaginal epithelial cells containing chlamydia bacteria Chlamydia pneumoniae.jpg
Vaginal epithelial cells containing chlamydia bacteria

Disease transmission

Sexually transmitted infections, including HIV are rarely transmitted across intact and healthy epithelium. These protective mechanisms are due to frequent exfoliation of the superficial cells, low pH, and innate and acquired immunity in the tissue. Research into the protective nature of the vaginal epithelium has been recommended as it would help in the design of topical medication and microbicides. [9]

Cancer

There are very rare malignant growths that can originate in the vaginal epithelium. [37] Some are only known through case studies. They are more common in older women. [38]

Inflammation

Cross section of vaginal epithelium in a post-menopausal woman VaginaHisto.jpg
Cross section of vaginal epithelium in a post-menopausal woman

Atrophy

The vaginal epithelium changes significantly when estrogen levels decrease at menopause. [46] Atrophic vaginitis [47] usually causes scant odorless discharge [48]

History

The vaginal epithelium has been studied since 1910 by a number of histologists. [32]

Research

The use of nanoparticles that can penetrate the cervical mucus (present in the vagina) and vaginal epithelium has been investigated to determine if medication can be administered in this manner to provide protection from infection of the Herpes simplex virus. [49] Nanoparticle drug administration into and through the vaginal epithelium to treat HIV infection is also being investigated. [50]

See also

Related Research Articles

<span class="mw-page-title-main">Cervix</span> Lower part of the uterus in the female reproductive system

The cervix or cervix uteri is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity. The human cervix has been documented anatomically since at least the time of Hippocrates, over 2,000 years ago. The cervix is approximately 4 cm long with a diameter of approximately 3 cm and tends to be described as a cylindrical shape, although the front and back walls of the cervix are contiguous. The size of the cervix changes throughout a women's life cycle. For example, during their fertile years of the reproductive cycle, females tend to have a larger cervix vis á vis postmenopausal females; likewise, females who have produced offspring have a larger sized cervix than females who have not produced offspring.

<span class="mw-page-title-main">Endometrium</span> Inner mucous membrane of the mammalian uterus

The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional layer thickens and then is shed during menstruation in humans and some other mammals, including other apes, Old World monkeys, some species of bat, the elephant shrew and the Cairo spiny mouse. In most other mammals, the endometrium is reabsorbed in the estrous cycle. During pregnancy, the glands and blood vessels in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta, which supplies oxygen and nutrition to the embryo and fetus. The speculated presence of an endometrial microbiota has been argued against.

<span class="mw-page-title-main">Vagina</span> Part of the female reproductive tract

In mammals and other animals, the vagina is the elastic, muscular reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix. The vaginal introitus is normally partly covered by a thin layer of mucosal tissue called the hymen. The vagina allows for copulation and birth. It also channels menstrual flow, which occurs in humans and closely related primates as part of the menstrual cycle.

<span class="mw-page-title-main">Bartholin's gland</span> Mucous glands located near the vaginal opening

The Bartholin's glands are two pea-sized compound alveolar glands located slightly posterior and to the left and right of the opening of the vagina. They secrete mucus to lubricate the vagina.

<span class="mw-page-title-main">Epithelium</span> Tissue lining the surfaces of organs in animals

Epithelium or epithelial tissue is a thin, continuous, protective layer of compactly packed cells with little extracellular matrix. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. These tissues also lack blood or lymph supply. The tissue is supplied by nerves.

Vaginitis, also known as vulvovaginitis, is inflammation of the vagina and vulva. Symptoms may include itching, burning, pain, discharge, and a bad smell. Certain types of vaginitis may result in complications during pregnancy.

<span class="mw-page-title-main">Epidermis</span> Outermost of the three layers that make up the skin

The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.

<span class="mw-page-title-main">Transitional epithelium</span> A type of tissue

Transitional epithelium is a type of stratified epithelium. Transitional epithelium is a type of tissue that changes shape in response to stretching. The transitional epithelium usually appears cuboidal when relaxed and squamous when stretched. This tissue consists of multiple layers of epithelial cells which can contract and expand in order to adapt to the degree of distension needed. Transitional epithelium lines the organs of the urinary system and is known here as urothelium. The bladder, for example, has a need for great distension.

<span class="mw-page-title-main">Cervical intraepithelial neoplasia</span> Medical condition

Cervical intraepithelial neoplasia (CIN), also known as cervical dysplasia, is the abnormal growth of cells on the surface of the cervix that could potentially lead to cervical cancer. More specifically, CIN refers to the potentially precancerous transformation of cells of the cervix.

Hypoestrogenism, or estrogen deficiency, refers to a lower than normal level of estrogen. It is an umbrella term used to describe estrogen deficiency in various conditions. Estrogen deficiency is also associated with an increased risk of cardiovascular disease, and has been linked to diseases like urinary tract infections and osteoporosis.

<span class="mw-page-title-main">Vaginal discharge</span> Medical condition

Vaginal discharge is a mixture of liquid, cells, and bacteria that lubricate and protect the vagina. This mixture is constantly produced by the cells of the vagina and cervix, and it exits the body through the vaginal opening. The composition, amount, and quality of discharge varies between individuals and can vary throughout the menstrual cycle and throughout the stages of sexual and reproductive development. Normal vaginal discharge may have a thin, watery consistency or a thick, sticky consistency, and it may be clear or white in color. Normal vaginal discharge may be large in volume but typically does not have a strong odor, nor is it typically associated with itching or pain. While most discharge is considered physiologic or represents normal functioning of the body, some changes in discharge can reflect infection or other pathological processes. Infections that may cause changes in vaginal discharge include vaginal yeast infections, bacterial vaginosis, and sexually transmitted infections. The characteristics of abnormal vaginal discharge vary depending on the cause, but common features include a change in color, a foul odor, and associated symptoms such as itching, burning, pelvic pain, or pain during sexual intercourse.

<span class="mw-page-title-main">Respiratory epithelium</span> Mucosa that serves to moisten and protect the airways

Respiratory epithelium, or airway epithelium, is a type of ciliated columnar epithelium found lining most of the respiratory tract as respiratory mucosa, where it serves to moisten and protect the airways. It is not present in the vocal cords of the larynx, or the oropharynx and laryngopharynx, where instead the epithelium is stratified squamous. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the secretion of mucus and the action of mucociliary clearance.

<span class="mw-page-title-main">Cervical canal</span> Canal of the uterine cervix

The cervical canal is the spindle-shaped, flattened canal of the cervix which connects the vagina to the main cavity of the uterus in most mammals.

<span class="mw-page-title-main">Stratified squamous epithelium</span> Tissue type

A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface. In the deeper layers, the cells may be columnar or cuboidal. There are no intercellular spaces. This type of epithelium is well suited to areas in the body subject to constant abrasion, as the thickest layers can be sequentially sloughed off and replaced before the basement membrane is exposed. It forms the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina.

<span class="mw-page-title-main">Cervical ectropion</span> Presence of internal cells of the cervical canal outside the cervix

Cervical ectropion is a condition in which the cells from the 'inside' of the cervical canal, known as glandular cells, are present on the 'outside' of the vaginal portion of the cervix. The cells on the 'outside' of the cervix are typically squamous epithelial cells. Where the two cells meet is called the transformation zone, also known as the stratified squamous epithelium. Cervical ectropion can be grossly indistinguishable from early cervical cancer and must be evaluated by a physician to determine risks and prognosis. It may be found incidentally when a vaginal examination is done. The area may look red because the glandular cells are red. While many women are born with cervical ectropion, it can be caused by a number of reasons, such as:

The junctional epithelium (JE) is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. The probing depth of the gingival sulcus is measured by a calibrated periodontal probe. In a healthy-case scenario, the probe is gently inserted, slides by the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). However, the probing depth of the gingival sulcus may be considerably different from the true histological gingival sulcus depth.

<span class="mw-page-title-main">Ospemifene</span> Chemical compound

Ospemifene is an oral medication indicated for the treatment of dyspareunia – pain during sexual intercourse – encountered by some women, more often in those who are post-menopausal. Ospemifene is a selective estrogen receptor modulator (SERM) acting similarly to an estrogen on the vaginal epithelium, building vaginal wall thickness which in turn reduces the pain associated with dyspareunia. Dyspareunia is most commonly caused by "vulvar and vaginal atrophy."

<span class="mw-page-title-main">Atrophic vaginitis</span> Medical condition

Atrophic vaginitis is inflammation of the vagina as a result of tissue thinning due to low estrogen levels. Symptoms may include pain with sex, vaginal itchiness or dryness, and an urge to urinate or burning with urination. It generally does not resolve without ongoing treatment. Complications may include urinary tract infections. Atrophic vaginitis as well as vulvovaginal atrophy, bladder and urethral dysfunctions are a group of conditions that constitute Genitourinary Syndrome of Menopause (GSM). Diagnosis is typically based on symptoms.

Vaginal cytology is a microscopic examination of cells from the vaginal epithelium. In veterinary medicine, it helps differentiate the stages of the mammalian estrous cycle because the vaginal epithelium changes in response to sex hormone levels; practically, it is used to distinguish when a female canine is at a particular point in the estrous cycle. In a normal vaginal smear, lactational cells, navicular cells, endocervical cells, endometrial cells, trophoblastic cells, and leucocytes may be present.

<span class="mw-page-title-main">Vaginal cysts</span> Benign growths of the vaginal epithelium

Vaginal cysts are uncommon benign cysts that develop in the vaginal wall. The type of epithelial tissue lining a cyst is used to classify these growths. They can be congenital. They can present in childhood and adulthood. The most common type is the squamous inclusion cyst. It develops within vaginal tissue present at the site of an episiotomy or other vaginal surgical sites. In most instances they do not cause symptoms and present with few or no complications. A vaginal cyst can develop on the surface of the vaginal epithelium or in deeper layers. Often, they are found by the woman herself and as an incidental finding during a routine pelvic examination. Vaginal cysts can mimic other structures that protrude from the vagina such as a rectocele and cystocele. Some cysts can be distinguished visually but most will need a biopsy to determine the type. Vaginal cysts can vary in size and can grow as large as 7 cm. Other cysts can be present on the vaginal wall though mostly these can be differentiated. Vaginal cysts can often be palpated (felt) by a clinician. Vaginal cysts are one type of vaginal mass, others include cancers and tumors. The prevalence of vaginal cysts is uncertain since many go unreported but it is estimated that 1 out of 200 women have a vaginal cyst. Vaginal cysts may initially be discovered during pregnancy and childbirth. These are then treated to provide an unobstructed delivery of the infant. Growths that originate from the urethra and other tissue can present as cysts of the vagina.

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