Ultrastructure of the normal human urethra

Human urethral epithelium: immunohistochemical demonstration of secretory IgA

Male human urethral epithelium was treated for the immunohistochemical demonstration of secretory IgA in order to verify its own possible antimicrobial properties. An intense immunoreactivity for sIgA in the entire cytoplasm and at the luminal surface of the apical epithelial cells was observed. The results suggest that sIgA play a prominent role in the local defense mechanisms of the urethra. Such mucosal defense mechanisms may be of significance in the defense of the urinary and genital tract against ascending infections.

Different epithelia in the distal human male urethra

The distal segment of the human male urethra, in particular the fossa navicularis, was studied with light- and electron microscopy as well as by means of histochemical and immunocytochemical methods. The fossa navicularis of the urethra contains a circumscribed zone of extremely thick, non-keratinized stratified squamous epithelium composed of cells containing a large amount of glycogen. These cells lack acid phosphatase activity and lysozyme-like immunoreactivity, both of which can be demonstrated to varying extents in the other zones of the distal male urethra. These glycogenrich cells are considered to be the substrate for an endogenous flora of lactobacteria, whereas the acid-phosphatase activity and the lysozyme-like immunoreactivity indicate the presence of macrophages and the secretion of bactericidal agents at the epithelial surface. These observations suggest that the different zones with heterogeneous properties in the distal male urethra probably represent a defense system against the invasion of pathogenic microorganisms. Moreover, the glycogen-rich zone, which resembles the glycogen-rich epithelium of the vagina, is estrogen-dependent. This is demonstrated in cases of sex reversal in which after long-lasting estrogen treatment the glycogen-rich zone becomes extremely extended by displacement of the neighbouring epithelium.

Evidence of mucin M1 antigens in seminal plasma and normal cells of human prostatic urethra in relation to embryonic development and tumors

By employing immunoperoxidase methodology, using monoclonal antibodies against the peptide core of gastric mucins (M1 antigens), we demonstrate the presence of M1 mucin-producing cells that are associated with the prostatic urethral epithelium and located mainly in the veru montanum area near the prostatic ductal and utriculus junctions. The significance of these M1 cells is not yet clear. Using an immunoradiometric assay, these M1 mucins were found predominantly in the prostatic fraction obtained from seminal plasma. By chromatography on Sepharose 6B and 2B and cesium chloride gradient centrifugation, we demonstrate that high-molecular-weight components (greater than 10(7) Da) show a density of 1.45 g/ml, similar to mucins, and are immunochemically related to peptidic gastric M1 mucins. The particular location of these M1 antigens in prostatic adult urethra and their fetal expression in cloacal structures suggest that, in males, the prostatic urethral epithelium includes some remnant cells from the enteric cloaca. Finally, the presence of mucin-containing cells in the prostatic urethra could possibly explain the histogenesis of the rare benign villous tumors and primary mucinous adenocarcinomas arising from the prostatic urethral epithelium.

Ultrastructure of human male urethra

The morphological features of human male urethra lining epithelium have been investigated by means of SEM at the various portions of the organ. The characteristics of the epithelial cells have been described and the significance of different morphological pattern is discussed.

Scanning electron microscopic observations on the epithelium of the human spongy urethra

The human spongy urethras of individuals submitted to emasculation because of glans carcinoma have been studied by means of scanning electron microscopy. The luminal surface of the organ shows longitudinal folds and small glandular openings, surrounded by epithelial elements arranged in form of rosettes. Spermatozoa, partially degenerated, adhere to the epithelium. The slightly prominent apices of the superficial epithelial cells are more or less polygonal in shape and covered with short microvilli among which small granules as possible morphological expression of a secretory activity are detectable. Only seldom microplicae, intermingled with microvilli, can be observed. Additionally, some apices appear swollen and protrude into the lumen. Such a pattern may be escalated so that a cell seems to transform itself into a globular mass and then is expulsed from the epithelial surface. Sometimes an epithelial cell appears empty of its contents: only the crumpled plasmalemma remains. This may represent the morphological expression of an apocrine or holocrine secretory activity of the superficial epithelium. In few cases, the proximal portion of the spongy urethra shows small groups of ciliated elements.

Scanning electron microscopic observations on the epithelium of the human prostatic urethra

The human prostatic urethra has been investigated by means of scanning electron microscopy. On the posterior wall of the urethra, the seminal colliculus with the orifices of the ejaculatory ducts is clearly detectable. The upper portion of the prostatic urethra shows a typical transitional epithelium with large superficial cells of a ruffled appearance. In the lower portion of the organ (underneath the openings of the ejaculatory ducts), the apical pattern of the cells varies considerably. Four main aspects are recognizable: apices provided with microvilli, dome-shaped apices with an almost smooth surface, large apices with labyrinthic microplicae and ciliated apices. Also, apices showing intermediate characteristics can be noted. The functional significance of the morphological patterns as well as the possibility of a transition among the various types of surface structures are discussed.

A histochemical and ultrastructural study of human urethral uroepithelium

The ultrastructure and histochemistry of the human urethral mucosa was studied. By scanning electronmicroscopy (SEM) the cover cell of the urethra was found to be polygonal and with a surface topography characterized by numerous microvilli and micro-ridges. By transmission electronmicroscopy (TEM) the cover cells were shown to be interconnected with tight junctions but to lack the asymmetric luminal membrane and the fusiform vacuoles that characterize urothelium above the bladder neck. Histochemical analyses showed the human urethral cells to harbour large amounts of glycogen, and the glycocalyx facing the urethral lumen displayed high affinity for alcian blue and colloidal iron, indicating the presence of acid mucopolysaccharides. The reactivity with alcian blue appeared at pH 2.5, but was abolished by pre-treatment with sialidase. Studies with TEM or using SEM with energy-dispersive X-ray spectrometry (EDX) confirmed the high content of acid mucopolysaccharides in the luminal glycocalyx of the cover cells by demonstrating high binding capacity for ruthenium red. The quantitative binding of ruthenium red was not influenced by pH shifts between 4.5 and 7.5. Utilizing the SEM + EDX technique, small variations in quantity of negative charge (i.e. of bound ruthenium red) were detected within individual cover cells, but considerable variations were found between cells. The significance of these physicochemical properties of the human urethral lining is discussed with special reference to the previously demonstrated liability of this mucosal surface to interact with microorganisms such as Escherichia coli, Staphylococcus saprophyticus and Neisseria gonorrhoeae.