Penile Embryology and Anatomy

Differentiation, 1999

The most widely accepted mechanism of male urethral development proposes that the urethral plate is elevated by urethral folds which fuse ventrally in a proximal-to-distal sequence. Unlike its proximal counterpart, the urethra which forms within the glans is lined by a stratified squamous epithelium and has a more controversial development. One theory supports the idea that fusion of the urethral folds extends all the way to the tip of the glans. Another theory suggests that a solid ectodermal ingrowth of epidermis canalizes the glandar urethra. We hypothesized that the use of immunohistochemical staining and tissue recombinant grafting would delineate the epithelia involved and lend clues to their origin. Thirty-six human fetal phallic specimens of gestational ages 5-22 weeks were sectioned and stained immunohistochemically with antibodies raised against different cytokeratins. Evaluation of the sections showed that the urethral plate, an extension of the urogenital sinus, extended to the tip of the phallus and maintained patency and continuity throughout the process of urethral development. The entire urethra, including the glans portion, was formed by dorsal extension and disintegration of the urethal plate combined with ventral growth and fusion of the urethral folds. Sections of the distal glandar urethra showed no evidence of a solid ectodermal ingrowth. Rather, immunostaining results at different ages suggested differentiation of the endodermal urethral plate into a stratified squamous epithelium. To determine whether urothelium could be induced to express a stratified squamous phenotype, mouse fetal bladder epithelium was combined with rat fetal genital tubercle mes-enchyme and grown under the renal capsule of athymic mice. The bladder epithelium differentiated into a stratified squamous epithelium. Thus, proper mesenchymal signaling may induce differentiation of urothelium into a stratified squamous phenotype, such as during development of the urethra of the glans penis.

Seminars in pediatric surgery, 2011

Faulty ventral openings of the urethra constitute a broad spectrum of malformations that are subsumed under the term "hypospadia." The normal development of the urethra and the genitals critically depends on the following events: (a) formation of the external genitalia, (b) fate of the cloacal membrane, and (c) formation of the distal urethra. The purpose of this study was to demonstrate these events using microsurgical techniques and scanning electron microscopy in staged rat embryos.

Journal of Anatomy, 2005

The structure of the striated urethral sphincter, the so-called rhabdosphincter, remains the subject of controversy.

Journal of Anatomy, 1999

The aim of this study was to provide a comprehensive description of both penile innervation and vascularisation. Eighty-five male cadavers were examined through gross and microscopic anatomical analysis. The pelvic nerve plexus had both parasympathetic and sympathetic roots. It was distributed to the external urethral sphincter giving rise to cavernous nerves which anastomosed in 70 % of the cases with the pudendal nerve in the penile root. Accessory pudendal arteries were present in the pelvis in 70 % of the cases, anastomosing in 70 % of the cases with the cavernous arteries that originated from the pudendal arteries. Transalbugineal anastomoses were always seen between the cavernous artery and the spongiosal arterial network. There were 2 venous pathways, 1 in the pelvis and 1 in the perineum with a common origin from the deep dorsal penile vein. It is concluded that there are 2 neurovascular pathways destined for the penis that are topographically distinct. One is located in the pelvis and the other in the perineum. We were unable to determine the functional balance between these 2 anastomosing pathways but experimental data have shown that they are both involved in penile erection. These 2 neurovascular pathways, above and below the levator ani, together with their anastomoses, form a neurovascular loop around the levator ani.

European Urology, 2005

Objectives: The precise location, origin and nature of nerve fibers innervating the male urethral sphincter have not been clearly established. Classical anatomical studies based on cadaver dissections have provided conflicting results concerning the location of somatic and autonomic nerve fibers. This study was designed to identify nerve fibers innervating the male urethral sphincter and to provide a three-dimensional representation of their tissue relations in the human male fetus. Materials and methods: Histology and immunohistochemistry (Hematein-Eosin-Safran, Luxol Fast Blue, Protein S 100 immunolabeling and smooth fibers actin immunolabeling) were performed in male external urethral sphincter of ten male fetuses (114-342 mm crown-rump length). Three-dimensional reconstruction of the urethral structure and innervation were obtained from serial sections using Surf Driver 3.5.3 software. Results: The three-dimensional reconstruction of the same section levels with different strains allowed to identify the precise structure of the muscular layers and the nature of nervous elements (myelinated and unmyelinated), their distributions and their relations with the urethral wall, the prostate and the seminal vesicles. Conclusion: Histological and immunohistochemical three-dimensional reconstruction of the nervous elements of the urethral sphincter gives a very didactical understanding of the three dimensional arrangement of the urethral nerves and their relationships with the urethral layers. It allows a better understanding of the origin, the course and the nature of the nervous elements participating in the urinary continence.

The Journal of Urology, 1998

Purpose: We investigated the anatomical relationship between the urethra and the surrounding erectile tissue, and reviewed the appropriateness of the current nomenclature used to describe this anatomy.

Differentiation

American Journal of Anatomy, 1991

As a basis for understanding the mechanism of erection in an animal model frequently used in research in reproductive biology, the angioarchitecture of the penis of the rat has been described using scanning electron microscopy. Study of the penile vasculature of the rat indicates that the corpora cavernosa penis and the corpus spongiosum are independent erectile tissues, each with its own arterial and venous vessels. The large vascular spaces and abundant smooth muscle of the penile crura are compatible with its role in regulating blood flow to more distal penile tissues. Helicine arteries of the crura, but not the parent deep penile artery or arteries elsewhere, have muscular cushions in their walls. The venous drainage of the penile crura is via subtunical veins which are thought to be compressed during erection to elevate pressure within the penis. Large, paired cavernous veins drain the shaft of the penis. A unique method for inhibiting blood flow from the penis is indicated by the division of the cavernous veins into smaller channels prior to joining the subtunical venous plexus. Erectile tissue in the bifid origins of the corpus spongiosum has abundant cavernous muscle, while in the remainder of the corpus spongiosum little smooth muscle lines the cavernous spaces. The cavernous spaces on either side of the urethra coalesce to form vessels, each of which communicates with cavernous spaces in the glans. In addition, a bypass of the glans is effected by communication of these vessels directly with the deep dorsal vein. The apparent absence of muscular pads in vessels of the spongiosum, the relative paucity of cavernous smooth muscle, and the ample venous drainage provided by the deep dorsal vein may account for the lack of a venous occlusive mechanism similar to that of the corpora cavernosa penis.

Differentiation; research in biological diversity

This paper addresses the developmental mechanisms of formation of the mouse and human penile urethra and the possibility that two disparate mechanisms are at play. It has been suggested that the entire penile urethra of the mouse forms via direct canalization of the endodermal urethral plate. While this mechanism surely accounts for development of the proximal portion of the mouse penile urethra, we suggest that the distal portion of the mouse penile urethra forms via a series of epithelial fusion events. Through review of the recent literature in combination with new data, it is unlikely that the entire mouse urethra is formed from the endodermal urethral plate due in part to the fact that from E14 onward the urethral plate is not present in the distal aspect of the genital tubercle. Formation of the distal portion of the mouse urethra receives substantial contribution from the preputial swellings that form the preputial-urethral groove and subsequently the preputial-urethral canal...

Journal of Urology, 2006