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PubMed1992

Fine structure of the dorsal lingual epithelium of the Japanese monkey Macaca fuscata fuscata.

Filiform papillae, which were densely distributed all over the dorsal surface of the lingual body, were crown-shaped, with a central, circular area that sloped in the anterior direction and several branches that surrounded it in a semicircle from the back of the central area. Dome-shaped, fungiform papillae were scattered among these filiform papillae. At the posterior end of the lingual body, there were four circumvallate papillae. Prominent microridges and elevated intercellular borders were widely distributed in the central area of the filiform papillae and the interpapillar region. On the surface of the branches of the filiform papillae, microridges were rarely seen. On the surface of the fungiform papillae, indistinct microridges were observed. Histologically, the dorsal lingual epithelium revealed three different regions: the epithelium on the anterior side of the filiform papillae, the epithelium on the posterior side of the filiform papillae and the interpapillar epithelium. Whereas the basal and suprabasal cells are similar throughout, differences characterize the intermediate and surface layers. Keratohyalin granules appear predominantly in the intermediate layer in the epithelium on the anterior side of filiform papillae. In the epithelium on the posterior side of the filiform papillae, no keratohyalin granules occur and, instead, tonofibrils are prominent. The cells become significantly flattened. In the interpapillar epithelium, no keratohyalin granules are visible, and the tonofilaments occupy almost the entire cytoplasm of most cells in the intermediate and surface layers. The cells are larger in volume in these layers.

Animals↗

PubMed2003

Impact of the environment on the mammalian corneal epithelium.

PURPOSE: To evaluate whether the content of ascorbic acid in the corneal epithelium and aqueous humor reflects seasonal fluctuations in parallel with environmental changes. METHODS: Reindeer, cattle, rabbits, and humans were examined, to cover a broad spectrum of overlapping habitats. Ascorbic acid was determined by high-performance liquid chromatography. The thickness of the corneal epithelium was measured, and the number of cells was counted in the tissue sections. RESULTS: Three groups of reindeer eyes were used, two of them collected during summer, the third group during winter. Ascorbate content did not show seasonal variation in either the corneal epithelium or the aqueous humor, whereas epithelial thickness and number of cells decreased significantly from summer to winter. In cattle, ascorbate content, thickness of the epithelium, and number of cells were lower in animals tended indoors compared with those tended outdoors, whereas ascorbate level in the aqueous humor remained similar in both cases. The rabbit showed significantly reduced ascorbate content in the corneal epithelium but not in the aqueous humor in tarsorrhaphy-treated eyes. This procedure did not change epithelial thickness, but the number of cells was slightly increased. The mean epithelial thickness in human corneas successively decreased with increasing latitude and decreasing radiation exposure from the summer season in Oslo to the midnight sun, polar night, conditions in Tromsø, 10 degrees far north, although the differences did not reach statistical significance. CONCLUSIONS: Ambient radiation is needed to sustain high ascorbic acid concentration in the corneal epithelium. Corneal epithelial thickness and number of cells are prone to seasonal fluctuations regulated by ambient radiation. In contrast, ascorbate content of the aqueous humor is uninfluenced by environmental change. It is suggested that seasonal adaptation of mammalian corneal epithelium in response to variation in ambient radiation may be nature's strategy for countering radiation damage to the eye.

Adult↗

PubMed2004

CD95 ligand expression on corneal epithelium and endothelium influences the fates of orthotopic and heterotopic corneal allografts in mice.

PURPOSE: To determine the extent to which CD95 ligand (CD95L) expressed on corneal epithelium and endothelium influences survival of cornea grafts placed orthotopically and heterotopically in the anterior chamber (AC), an immune-privileged site. METHODS: Corneas from eyes of C57BL/6 (B6) and B6.gld (CD95L deficient) mice were (1) rendered into small full-thickness fragments, with or without an epithelial layer, and placed behind recipient corneas in the ACs of BALB/c eyes, while BALB/c corneas were similarly implanted in eyes of B6 and B6.lpr (CD95 deficient) mice; or (2) corneas were grafted orthotopically in BALB/c eyes as intact corneas or as composite corneas in which epithelium from one donor source was layered in vitro onto epithelium-deprived stroma+endothelium from another donor source before grafting. The fate of the grafts was assessed clinically and histologically, and the capacity of the grafts to sensitize recipient mice to donor alloantigens (delayed hypersensitivity, DH) was evaluated. RESULTS: Allogeneic, full-thickness B6.gld corneal fragment grafts placed in the AC of BALB/c mice were rejected and sensitized their recipients, whereas epithelium-deprived B6.gld cornea fragments survived indefinitely and failed to sensitize their recipients. BALB/c corneal fragment grafts placed in the AC of C57BL/6 or B6.lpr eyes were rejected. Orthotopic cornea grafts composed of B6.gld epithelium layered onto wild-type B6 stroma and endothelium were rejected at a tempo and incidence similar to full-thickness B6 grafts, whereas orthotopic composite cornea grafts containing B6 epithelium layered onto B6.gld stroma+endothelium were vigorously rejected. CONCLUSIONS: CD95L expression on epithelium of full-thickness cornea fragment grafts placed in the anterior chamber of BALB/c eyes protects these heterotopic grafts from rejection but has only a trivial role to play in determining the fate of orthotopic corneal grafts. In the latter type of corneal grafts, CD95L expression on the endothelium plays an essential role in preventing graft rejection.

Animals↗

PubMed1992

A light and electron microscopic anterograde WGA-HRP tracing study on the sensory innervation of junctional and sulcular epithelium in the rat molar.

The sensory innervation of junctional and oral sulcular epithelium was investigated by use of anterograde transport of wheat-germ agglutinin-horseradish peroxidase from the trigeminal ganglion. By light microscopy, labeled intra-epithelial nerve fibers were observed forming a dense plexus in the apical two-thirds of the junctional epithelium, with some fibers located near the enamel space. Occasional fibers extended coronally to the sulcus bottom. By electron microscopy, labeled intra-epithelial axon terminals or varicosities were demonstrated to be in close contact with both junctional epithelial cells and neutrophils. These varicosities, which were occasionally surrounded by the cytoplasmic processes of epithelial cells or neutrophils, frequently contained large granular and small clear vesicles. In contrast to the junctional epithelium, the oral sulcular epithelium was sparsely innervated, except for the transition region between the oral sulcular epithelium and the junctional epithelium, where a dense innervation by labeled intraepithelial fibers was found. These fibers extended as far as the stratum spinosum. Electron microscopy revealed mitochondria-filled profiles of varicosities between epithelial cells. This study shows differences in the distribution and ultrastructure of sensory nerves between the junctional and oral sulcular epithelia, and further provides morphological evidence that sensory nerves in the junctional epithelium come into contact not only with epithelial cells but also with neutrophils.

Animals↗

PubMed1996

Bovine tracheal responsiveness in vitro: role of the epithelium and nitric oxide.

Airway epithelium releases inhibitory factors, such as nitric oxide (NO) and prostaglandin E2 (PGE2), which may counteract bronchoconstriction. We investigated whether epithelium-derived inhibitory substances exert a crucial influence on bovine tracheal responsiveness in vitro. Isotonic and isometric contractions in response to histamine of intact and epithelium-denuded tracheal smooth muscle strips were compared. In addition, the effects of L-arginine (L-arg), N(G)-nitro-L-arginine methyl esther (L-NAME), and N(G)-monomethyl L-arginine (L-NMMA) on histamine responsiveness were investigated. The release of NO and PGE2 from tracheal epithelium was measured. Removal of the epithelium from tracheal smooth muscle strips did not change the negative log of the concentration of histamine producing half the maximal effect (pD2) or the maximal effect (Emax). Incubation of the tissues for 25 min with L-arg or L-NAME did not influence basal tone or the contractions induced by histamine. However, incubation with L-NMMA increased the basal tone and caused a slight hyporesponsiveness to histamine. S-nitroso-N-acetyl-penicillamine (SNAP, a direct NO donor) reversed the contraction induced by histamine in a concentration-dependent manner. Stimulation of the epithelial layer by 0.1 microM histamine increased the release of NO 3-4 fold compared to basal levels; this effect was completely inhibited in the presence of L-NMMA. In addition, 1 mM histamine caused a significant increase in the release of PGE2 from the epithelial tissue. In conclusion, no functional inhibitory influence of the epithelium can be identified in bovine airways. The S-nitroso-N-acetyl-penicillamine-induced relaxation demonstrates the presence of a nitric oxide sensitive pathway in bovine airways. However, the amounts of nitric oxide and prostaglandin E2 released from bovine tracheal epithelium are probably too low to exert a significant effect on the histamine-induced contractions.

Animals↗

PubMed2006

Reinstatement of "germinal epithelium" of the ovary.

BACKGROUND: The existing dogma that the former term ovarian "germinal epithelium" resulted from a mistaken belief that it could give rise to new germ cells is now strongly challenged. DISCUSSION: Two years ago, a research group of the University of Tennessee led by Antonin Bukovsky successfully demonstrated the oogenic process from the human ovarian covering epithelium now commonly called the ovarian surface epithelium. They showed the new oocyte with zona pellucida and granulosa cells, both originated from the surface epithelium arising from mesenchymal cells in the tunica albuginea, and stressed that the human ovary could form primary follicles throughout the reproductive period. This gives a big impact not only to the field of reproductive medicine, but also to the oncologic area. The surface epithelium is regarded as the major source of ovarian cancers, and most of the neoplasms exhibit the histology resembling müllerian epithelia. Since the differentiating capability of the surface epithelium has now expanded, the histologic range of the neoplasms in this category may extend to include both germ cell tumors and sex cord-stromal cell tumors. SUMMARY: Since the oogenic capability of ovarian surface cells has been proven, it is now believed that the oocytes can originate from them. The term "germinal epithelium", hence, might reasonably be reinstated.

Animals↗

PubMed1993

Effect of aging on endogenous level of 5 alpha-dihydrotestosterone, testosterone, estradiol, and estrone in epithelium and stroma of normal and hyperplastic human prostate.

It is widely believed that benign prostatic hyperplasia (BPH) is associated with aging. Thus, the question arises whether or not a correlation exists between the well known prostatic androgen and estrogen accumulation and aging. To address this question, we measured 5 alpha-dihydrotestosterone (DHT), testosterone, estradiol, and estrone in epithelium and stroma of six normal (NPR) and 19 BPH and correlated the values with the age of the donors (26-87 yr). The mean DHT level in NPR epithelium was significantly higher than in NPR stroma, and also significantly higher than in epithelium and stroma of BPH. The epithelial DHT level of NPR and BPH decreased with age, the correlation being statistically significant. The stromal DHT level of NPR and BPH showed no correlation with age. Concerning testosterone, generally rather low values were found which showed no correlation with age. The mean levels of estradiol and estrone were significantly higher in BPH stroma as compared to BPH epithelium as well as to NPR epithelium and stroma. In NPR, the mean levels of estradiol and estrone were significantly higher in epithelium than stroma. In NPR and BPH, the stromal estradiol and estrone levels increased significantly with age. In epithelium such a correlation between the estrogen levels and age was not found. Our results indicate that the prostatic accumulation of DHT, estradiol, and estrone is in part intimately correlated with aging, leading with increasing age to a dramatic increase of the estrogen/androgen ratio particularly in stroma of BPH.

Adult↗

PubMed1996

Protein and messenger ribonucleic acid (mRNA) for the type 1 insulin-like growth factor (IGF) receptor is decreased and IGF-II mRNA is increased in human prostate carcinoma compared to benign prostate epithelium.

Insulin-like growth factors (IGFs) and the type 1 IGF receptor (IGF-R) are involved in normal growth and development of the human prostate. Changes in levels of IGF-R and IGFs have been shown for several malignancies. Immunohistochemistry and in situ hybridization were performed to compare the expression of IGF-R and IGF-II in vivo in prostate tissue containing benign epithelium, high grade prostate intraepithelial neoplasia (PIN), and adenocarcinoma. Messenger ribonucleic acid (mRNA) hybridization signals and immunoreactivity for IGF-R were localized primarily to epithelial cells, with less signal in stroma. IGF-R mRNA was significantly decreased by 42% in PIN and 35% in cancer cells compared to that in benign epithelium (P < 0.0001). IGF-R immunostaining was significantly decreased by 32% in PIN and by 42% in malignant epithelium compared to that in benign epithelium (P < 0.004). IGF-II mRNA was also localized primarily to epithelial cells. IGF-II mRNA was significantly increased by 30% in adenocarcinoma compared to that in benign epithelium (P < 0.03). Immunoreactivity for IGF-II was localized to both stroma and epithelium. Protein levels for IGF-II were not significantly increased in cancer cells compared to those in benign epithelium. The decrease in the type 1 IGF receptor and increase in IGF-II mRNA may affect prostate cancer proliferation and differentiation.

Adenocarcinoma↗

PubMed2003

A novel function for Hedgehog signalling in retinal pigment epithelium differentiation.

Sonic hedgehog is involved in eye field separation along the proximodistal axis. We show that Hh signalling continues to be important in defining aspects of the proximodistal axis as the optic vesicle and optic cup mature. We show that two other Hedgehog proteins, Banded hedgehog and Cephalic hedgehog, related to the mouse Indian hedgehog and Desert hedgehog, respectively, are strongly expressed in the central retinal pigment epithelium but excluded from the peripheral pigment epithelium surrounding the ciliary marginal zone. By contrast, downstream components of the Hedgehog signalling pathway, Gli2, Gli3 and X-Smoothened, are expressed in this narrow peripheral epithelium. We show that this zone contains cells that are in the proliferative state. This equivalent region in the adult mammalian eye, the pigmented ciliary epithelium, has been identified as a zone in which retinal stem cells reside. These data, combined with double labelling and the use of other retinal pigment epithelium markers, show that the retinal pigment epithelium of tadpole embryos has a molecularly distinct peripheral to central axis. In addition, Gli2, Gli3 and X-Smoothened are also expressed in the neural retina, in the most peripheral region of the ciliary marginal zone, where retinal stem cells are found in Xenopus, suggesting that they are good markers for retinal stem cells. To test the role of the Hedgehog pathway at different stages of retinogenesis, we activated the pathway by injecting a dominant-negative form of PKA or blocking it by treating embryos with cyclopamine. Embryos injected or treated at early stages display clear proximodistal defects in the retina. Interestingly, the main phenotype of embryos treated with cyclopamine at late stages is a severe defect in RPE differentiation. This study thus provides new insights into the role of Hedgehog signalling in the formation of the proximodistal axis of the eye and the differentiation of retinal pigment epithelium.

Animals↗

PubMed1991

Substitution for mesenchyme by basement-membrane-like substratum and epidermal growth factor in inducing branching morphogenesis of mouse salivary epithelium.

Mouse salivary epithelium cannot undergo branching morphogenesis in the absence of the surrounding mesenchyme. To clarify the nature of the mesenchymal influence on the epithelium, we have investigated the culture conditions in which the epithelium could normally branch in the absence of mesenchymal cells. Combination of basement-membrane-like substratum (Matrigel) and epidermal growth factor (EGF) could substitute for the mesenchyme, the epithelium showing typical branching morphogenesis. Transforming growth factor alpha had the same effect as EGF. Matrigel plus basic fibroblast growth factor or transforming growth factor beta 1 and collagen gel plus EGF were not sufficient to support the branching of the epithelium. These results clearly reveal that the role of mesenchyme in salivary morphogenesis is both to provide the epithelium with an appropriate substratum and to accelerate growth of the epithelium.

Animals↗

PubMed1992

The epithelium of the dorsal marginal zone of Xenopus has organizer properties.

We have investigated the properties of the epithelial layer of the dorsal marginal zone (DMZ) of the Xenopus laevis early gastrula and found that it has inductive properties similar to those of the entire Spemann organizer. When grafts of the epithelial layer of the DMZ of early gastrulae labelled with fluorescein dextran were transplanted to the ventral sides of unlabelled host embryos, they induced secondary axes composed of notochord, somites and posterior neural tube. The organizer epithelium rescued embryos ventralized by UV irradiation, inducing notochord, somites and posterior neural tube in these embryos, while over 90% of ventralized controls showed no such structures. Combinations of organizer epithelium and ventral marginal zone (VMZ) in explants of the early gastrula resulted in convergence, extension and differentiation of dorsal mesodermal tissues, whereas similar recombinants of nonorganizer epithelium and the VMZ did none of these things. In all cases, the axial structures forming in response to epithelial grafts were composed of labelled graft and unlabelled host cells, indicating an induction by the organizer epithelium of dorsal, axial morphogenesis and tissue differentiation among mesodermal cells that otherwise showed non-axial development. Serial sectioning and scanning electron microscopy of control grafts shows that the epithelial organizer effect occurs in the absence of contaminating deep cells adhering to the epithelial grafts. However, labelled organizer epithelium grafted to the superficial cell layer contributed cells to deep mesodermal tissues, and organizer epithelium developed into mesodermal tissues when deliberately grafted into the deep region. This shows that these prospective endodermal epithelial cells are able to contribute to mesodermal, mesenchymal tissues when they move or are moved into the deep environment. These results suggest that in normal development, the endodermal epithelium may influence some aspects of the cell motility underlying the mediolateral intercalation (see Shih, J. and Keller, R. (1992) Development 116, 901-914), as well as the tissue differentiation of mesodermal cells. These results have implications for the analysis of mesoderm induction and for analysis of variations in the differentiation and morphogenetic function of the marginal zone in different species of amphibians.

Animals↗

PubMed1998

Differential expression and function of cadherin-6 during renal epithelium development.

The cadherin gene family encodes calcium-dependent adhesion molecules that promote homophilic interactions among cells. During embryogenesis, differential expression of cadherins can drive morphogenesis by stimulating cell aggregation, defining boundaries between groups of cells and promoting cell migration. In this report, the expression patterns of cadherins were examined by immunocytochemistry and in situ hybridization in the embryonic kidney, during the time when mesenchymal cells are phenotypically converted to epithelium and the pattern of the developing nephrons is established. At the time of mesenchymal induction, cadherin-11 is expressed in the mesenchyme but not in the ureteric bud epithelium, which expresses E-cadherin. The newly formed epithelium of the renal vesicle expresses E-cadherin near the ureteric bud tips and cadherin-6 more distally, suggesting that this primitive epithelium is already patterned with respect to progenitor cell types. In the s-shaped body, the cadherin expression patterns reflect the developmental fate of each region. The proximal tubule progenitors express cadherin-6, the distal tubule cells express E-cadherin, whereas the glomeruli express P-cadherin. Ultimately, cadherin-6 is down-regulated whereas E-cadherin expression remains in most, if not all, of the tubular epithelium. Antibodies generated against the extracellular domain of cadherin-6 inhibit aggregation of induced mesenchyme and the formation of mesenchyme-derived epithelium but do not disrupt ureteric bud branching in vitro. These data suggest that cadherin-6 function is required for the early aggregation of induced mesenchymal cells and their subsequent conversion to epithelium.

Animals↗

PubMed1980

Prostatic induction: interaction of epithelium and mesenchyme from normal wild-type mice and androgen-insensitive mice with testicular feminization.

The prostate gland develops from the urogenital sinus as epithelial buds projecting into the surrounding mesenchyme. The role of the mesenchyme in this process was determined using sinuses from normal and androgen-insensitive Tfm mice which are deficient in androgen receptors. Epithelium and mesenchyme from both types of sinus were separated and recombined and the recombinants grown in organ culture in the presence of testosterone. Recombinants consisting of normal epithelium and normal mesenchyme developed epithelial buds projecting into the surrounding mesenchyme but no buds were formed in recombinants of epithelium and mesenchyme from mutant mice. In recombinants of epithelium from mutant mice with normal mesenchyme the epithelium developed prostatic buds and the number was similar to that found if normal epithelium was associated with normal mesenchyme. In contrast, normal epithelium combined with mesenchyme from mutant mice failed to form prostatic buds. The results suggested that the mesenchyme determines the development of prostatic buds and that the lack of inductive capacity of the mesenchyme from mutant mice may be due to a deficiency of mesenchymal androgen receptors.

Androgen-Insensitivity Syndrome↗

PubMed1981

Relationships between epithelium and connective tissue in inflamed gingiva.

Since chronic inflammation has been associated with degenerative and proliferative responses in connective tissue and epithelium, it was decided to investigate quantitatively the proportions of epithelium and connective tissue in inflamed gingiva. Forty-five midfacial gingival sites were assessed prior to biopsy for the presence or absence of bleeding after probing using a controlled insertion force fo 25 g. In order to delineate the corresponding area for histologic analysis, a reference incision was made on the facial surface of the gingiva which demarcated the depth and mesio-distal extent of the area probed. Step-serial bucco-lingual sections were morphometrically analyzed to determine the percentages of epithelium, inflamed, and noninflamed connective tissues coronal to the reference incision. The data was compared with respect to the presence or absence of bleeding after probing. Specimens which bled after probing had significantly less epithelium and more connective tissue. The increase in overall connective tissue was due to a significant increase in the inflamed component, and it appeared that the decrease in epithelium corresponded to the increase in inflamed connective tissue. The findings of diminished epithelium overlying inflamed connective tissue reinforces the concept that connective tissue status is important for determining structure and function of epithelium.

Adult↗

PubMed1984

Pocket epithelium removal via crestal and subcrestal scalloped internal bevel incisions.

This study assessed the extent of pocket epithelium removal by crestal and subcrestal scalloped inverse bevel incisions during mucoperiosteal flap surgery. Fifty-six gingival biopsies were obtained from 52 participants, who had extractions of periodontally involved teeth. Sulcular incisions which severed the epithelial attachment served as controls. Experimental scalloped internal bevel incisions were made: (1) at the gingival crest extending apical to the osseous crest (crestal incision) and (2) 1 to 2 mm apical to the gingival margin extending apical to the osseous crest (subcrestal incision). In the two procedures the initial incisions were followed by sulcular incisions to sever the epithelial attachment. After both crestal and subcrestal incisions full thickness flaps were reflected, pocket contents were removed, and flaps were replaced against the teeth. Gingival biopsies were then obtained from control and experimental sites followed by extraction of teeth. All specimens were processed, embedded in paraffin, sectioned, stained with hematoxylin and eosin and examined for residual pocket epithelium. Control incisions eliminated pocket epithelium in two of 20 specimens. Crestal incisions eliminated pocket epithelium in 11 of 25 areas, while subcrestal incisions eliminated pocket epithelium in 13 of 25 areas. All 10 papillary areas treated by crestal incisions and 8 of the 10 papillary areas treated by subcrestal incisions displayed residual pocket epithelium. Neither crestal nor subcrestal scalloped internal bevel incisions consistently eliminated all pocket epithelium.

Adult↗

PubMed1990

The intermediate epithelium lining the nasopharynx of the Suncus murinus.

In the adult Suncus murinus, the rostral part of the nasopharynx is lined with the ciliated columnar epithelium continuing from the nasal cavity, while the laryngopharynx with the stratified squamous epithelium; i.e., the epithelium lining the caudal part of the nasopharynx forms the transitional zone between the ciliated columnar epithelium and the stratified squamous one. The epithelium shows gradations ranging from ciliated stratified low-columnar through stratified cuboidal to stratified squamous type. It is suggested that the epithelium is identical with the "intermediate epithelium (Nakano, 1986)".

Animals↗

PubMedDate not supplied

Junctions of squamous epithelium with middle ear mucosa.

Specimens obtained from the middle ear during surgery for cholesteatoma showed either abrupt junctions without metaplasia or junctions of varying width with metaplastic epithelium. Another form of junctional area showed pronounced inflammatory cell reaction with squamous epithelium projections growing into the stroma under the columnar epithelium. Immunofluorescent staining for cytokeratins showed distinct decoration of the columnar and metaplastic epithelia as well as of the basal cells of squamous epithelium. Prekeratin staining showed decoration of both squamous and metaplastic epithelium and no staining of the columnar epithelium. The findings suggest that metaplasia forms part of the migrating front of the squamous epithelium and alone plays no major role in cholesteatoma genesis.

Cholesteatoma↗

PubMed1988

Structure of the crypt epithelium in human palatine tonsils.

Material from human palatine tonsils from a group of 18 tonsillectomised patients aged 22 months to 8 years was studied by LM, TEM and SEM. Special attention was focused on the structure of the epithelium lining the tonsillar crypts. This is of a dynamic nature in the living organism. In contrast to the stratified squamous epithelium covering the oropharyngeal surface of the tonsil it was often reticulated and invaded by non-epithelial cells. However, it was not uniform throughout. When studied by LM and TEM, adjacent patches of epithelium varied in degree of reticularity. The reticulated epithelium was either covered by a thin layer of squamous cells, or this was disrupted in places where non-epithelial cells passed through. Hence the intact surface, as seen on the SEM, is not a reliable indication of the nature of the underlying structure of the epithelium. Small blood vessels were frequently observed in association with the reticulated epithelium. They formed numerous finger-like projections surrounded by a sleeve of subepithelial connective tissue, and also a fine capillary network within the epithelial thickness. It is proposed that such an organisation of the crypt epithelium offers favourable means for the capturing and processing of antigens by the palatine tonsils.

Blood Vessels↗