The penis is composed of 3 spongy cylinders. The three cylinders consist of paired corpora cavernosa and a single corpus spongiosum. The crural roots of the corpora cavernosa attach at the under surface of the ischiopubic rami as two separate structures. Such anatomy prevents the erect penis from sinking into the perineum when faced with an axially-oriented vaginal compressive load during intercourse.
This unique anatomic arrangement, however, unfortunately places the penile crus at great danger from crush injuries during blunt perineal trauma.
The tunica albuginea consists of layers of collagen which can accommodate a considerable degree of intracavernosal pressure prior to rupture. To function effectively, these fascial layers must provide the penis with a wall container capable of withstanding a high degree of rigidity and axial strength when erect, yet be supple when flaccid. The tunica must be able to elongate symmetrically and increase in girth with tumescence, assuring a straight erection.
The tensile strength of the tunica is approximately — mmHg making this fascia one of the most strong in the body. The average volume increase of the erect penis from the flaccid volume is 3-fold with a range from 1.
The mechanical properties of the tunica which allow for maximum volume changes of the erect penis are called tunica dispensability. Regions of the tunica with focal poor dispensability cause the erect penis to bend. The substance of the corpora cavernosa erectile tissue consists of numerous sinusoids lacunar spaces among interwoven trabeculae of smooth muscles and supporting connective tissue.
The corpora cavernosa sinusoids are widely communicative and larger in the center of the corpora, having a Swiss-cheese appearance. This fact enables the blood within the penis to transfer easily from the top to the bottom of the corpora.
This also enable the penis to have a common intracavernosal pressure and a common penile rigidity. The sinusoids are smaller in the periphery and have a grape-like appearance. Peripheral sinusoids have a greater individual surface area than central sinusoids. These characteristics aid in the passive process of corporal veno-occlusion by sub-tunical venule compression against the tunica albuginea. All lacunar spaces are lined with endothelial cells, thought previously to have only a slippery surface preventing blood clotting.
Recent research has revealed that endothelial cells have secretory function and synthesize factors involved in the regulation of corporal smooth muscle tone. The paired internal pudendal artery, a branch of the hypogastric artery is the main source of arterial blood supply to the penis.
The internal pudendal artery terminates when the artery divides into the scrotal and common penile artery. The common penile artery defines the condition whereby all red blood cells in the artery somehow end up in the penis. The common penile artery branches into 3 arteries, the bulbourethral, the dorsal and the cavernosal arteries. The common penile artery has direct apposition to the ischiopubic ramus. This artery is therefore commonly injured during blunt perineal traumatic events such as falling onto the top tube of a bicycle.
The penis is innervated by autonomic parasympathetic and sympathetic and somatic sensory and motor nerves. The cavernosal nerves are branches of the pelvic plexus that innervate the corpora cavernosa of the penis. Injury to this branch may occur during radical prostatectomy, during urethral surgery, such as internal urethrotomy and from electrocautery injury during transurethral surgery. The penis is the common output tract for urine and sperm. It is a structure that is under the control of a complex series of reflexes, neuronal and humoral control.
In this state the penis is capable of delivering the genetic material contained in the sperm during coitus. The penile erectile apparatus consists of paired vascular spongy organs corpora cavernosa that are closely attached to each other except in the proximal third. The corpus spongiosum with the urethra is related to the ventral aspect of the penile shaft and expands distally to from the glans penis.
The pendulous part of the penis if inches? The penile skin is continuous with that of the lower abdominal wall and continues over the glans penis to form the prepuce; it then folds itself to reattach at the coronal sulcus. The penile skin envelopes the shaft and can be moved freely over the erect organ. The superficial dorsal vein is seen in this layer of the fascia. Proximally, Buck;s fascia is attached to the perineal membrane; distally, it is tightly attached to the base of the glans penis at the coronal sulcus, where it fuses with the ends of the corpora.
Each is equipped with specific organs capable of producing specific…. The spermatic cord is actually a bundle of fibers and tissues that form a cord-like structure that runs through the abdominal region down to the…. The coccygeal muscle is located in the pelvic cavity. This muscle originates at the sacrospinous ligament, near the center of the pelvis, and inserts….
The vagus nerve is the longest of the 12 cranial nerves. Here, learn about its anatomy, functions, and the kinds of health problems that can occur. The fimbriae of the uterine tube, also known as fimbriae tubae, are small, fingerlike projections at the end of the fallopian tubes, through which…. Health Conditions Discover Plan Connect. Read this next. Leg Anatomy. The knowledge of such structures is necessary for understanding the normal physiology of the adult penis, commonly altered in different clinical or experimental situations [9] — [11].
Recently, it has been demonstrated the development of the area of the penis and corpora cavernosa and corpus spongiosum during the fetal period [12]. Nevertheless, until now, the morphology, development, modifications and distribution of the erectile tissue in the fetal penis is unknown.
Therefore, the objective of the present work is to analyze, qualitatively and quantitatively, in the corpora cavernosa CC and corpus spongiosum CS , the development of the main components of the penile erectile tissue, such as collagen, smooth muscle fibers and elastic system fibers, during the whole fetal period 13 to 36 weeks post-conception — WPC , providing normative patterns of growth.
We studied 56 penises obtained from normal human fetuses that had died of causes unrelated to the urogenital tract. All subjects were well preserved and none of them had any kind of detectable congenital malformation.
The gestational age of the fetuses ranged from 13 to 36 weeks post-conception corresponding to 15 to 38 menstrual weeks , and was estimated by the greatest foot length method [13] — [15]. We used 1 to 5 fetuses in each gestational age. The samples for histological analysis were obtained from the mid-shaft of the penis. All specimens were processed identically to minimize potential differences caused by processing. The sections were stained with Masson's trichrome for quantification of collagen, immunostaining for elastin for quantification of elastic system fibers and immunostaining for alpha-actin for quantification of smooth muscle fibers.
We obtained 5 sections from each penis and we analyzed 5 fields on each section and we performed 3 measurements for each field; therefore, we obtained 75 measurements for each penis, for each element analyzed. The result was the mean of percentages obtained for each color range. All quantifications were performed with a final magnification of X Both for corpus cavernosum and for corpus spongiosum, the quantifications were carried out in the same manner.
The Image J software 1. The percentage of collagen, smooth muscle fibers and elastic system fibers, was performed by using the plugin Color Segmentation. With the image in the software Figure 1 , by using the tool Point-Cross toolbar, the selection is performed by RGB color ranges and we can control the standard deviation.
After color selection is performed, each color is detected and, consequently, the percentage amount expressed. Masson's trichrome, X We performed the statistical analysis using the mean values for each element collagen, smooth muscle and elastic fibers by simple linear regression assessing the association between the variables analyzed with the fetal age. In addition, the correlation coefficient r and the p value were obtained for each regression analysis.
Software Graphpad Prism 5. During the fetal period in humans 13 to 36 weeks post-conception — WPC , the collagen accounted from The smooth muscle fibers accounted from 4. Immunostaining for alpha actin, X During the fetal period in humans 13 to 36 WPC , the elastic system fibers accounted from 1.
Immunostaining for elastin, X The linear regression analysis indicated that collagen, smooth muscle fibers and elastic system fibers concentration, correlated significantly and positively with fetal age, during the whole fetal period studied 13 to 36 WPC , and also during the second trimester 13 to 24 WPC and during the third trimester 25 to 36 WPC of gestation, when analyzed separately, both in corpus cavernosum and in corpus spongiosum. In addition, the linear regression analysis demonstrated a more intense growth rate of collagen, smooth muscle and elastic system fibers, during the second trimester of gestation, when compared to the third trimester, both in corpus cavernosum and in corpus spongiosum.
Figure 4 shows the correlation between collagen, muscle fibers and elastic system fibers, in percentage, in the corpus cavernosum and corpus spongiosum, with fetal age, during the fetal period studied 13 to 36 WPC. The points plotted represent the mean values obtained for each week studied. A Analysis in the corpus cavernosum. B Analysis in the corpus spongiosum. Previous studies from our group, in various organs of the urogenital system, including the penis, over the past 25 years, showed the importance of establishing growth patterns in normal human fetuses [4] , [5] , [16] — [18].
In addition, we studied the urogenital system in fetuses with congenital anomalies, as prune-belly syndrome and anencephaly, and compared these results with normal fetuses, with the view to possible use of anencephalic, for example, as potential donors of tissues and organs [19] — [21]. In the present work, we were able to include fetuses that covered almost all fetal period, 13 to 36 weeks post-conception, which corresponds from 15 to 38 menstrual weeks.
Concerning the penis, this kind of study is inexistent in the literature and is very important, because the transformations undergone by the organs during fetal development are very fast [22].
With reference to penis development during the fetal period, the only studies available in the literature, apart from that of our group [5] , [6] , [17] — [21] , [23] were performed by ultrasound or other imaging methods in utero, and were related only to penile length [24] — [27].
In this study, we confirmed that at the 13th week post-conception WPC , the corpora cavernosa and the corpus spongiosum, as well as the septa intra-cavernous, are already present as well individualized anatomical structures.
The quantitative analysis confirms these observations and this difference is maintained during all fetal period Figure 4. As gestational age increases, the collagen, both in the corpus cavernosum and corpus spongiosum, becomes more evident and increases in quantity Figure 1. The quantitative analysis shows objectively and confirms these results Figure 4. By linear regression analysis, comparing the growth of collagen both in the corpus cavernosum and corpus spongiosum , between the second and third trimester, we observed that collagen increases with a more intense rhythm in the second trimester.
A previous study from our laboratory [5] analyzing five normal fetuses at 28 WPC had already demonstrated that collagen is an important and well-differentiated component of the corpus cavernosum in the third trimester of gestation. Another previous study from our laboratory [23] , with normal human fetuses, infants, children and adults, using biochemical methods, showed that the total concentration of collagen in the fetal penis increased progressively, and almost doubled between the 17th and 33rd WPC, suggesting that major changes in the extracellular matrix of the penis occur in this gestational period.
Also, in a previous study from our laboratory, Costa et al. The linear regression analysis, comparing the proportion of collagen and smooth muscle fibers in corpus cavernosum and corpus spongiosum, objectively confirmed these observations Figure 4.
The linear regression analysis also showed that this difference is significant and is more pronounced in the third trimester of gestation. The quantification and the linear regression analysis showed objectively, however, that the increase in smooth muscle fibers is proportionally greater in the corpus cavernosum considering all fetal period Figure 4.
The linear regression analysis showed that the smooth muscle growth is strongly correlated with the fetal age and is more intense during the second trimester of gestation. Also, the quantitative analysis demonstrated a growth with predominance of smooth muscle in the trabeculae and a proportional decrease of collagen Figure 2.
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