Stretching the Tunica
Gentlemen and Pirates,
This is what we’re up against. The info below of particular interest to our strange clan of tunica stretchers concerns
1. Tunica tensile strength. (I assume safe tunica stretching is about stretching the tunica beyond its maximum at erection over a period of time, allowing recovery and then doing it again…and not tearing it! Read last sentence. Ouch.)
2. Elastin as a component of tunica.
3. Flaccid to erect volume ratios.
4. Varying thickness and tensile strength of tunica in different parts of penis; Perhaps some angles of erect bends are more effective than others.
5. Even pressure throughout corpora cavernosa.
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 1200 - 1500 mmHg making this fascia one of the most strong in the body. Approximately 5% of the tunica is elastin which enables the penis to develop elongation. The average volume increase of the erect penis from the flaccid volume is 3-fold with a range from 1.7 - 5 fold. 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. This focal tunical abnormality in dispensability
is called Peyronie’s disease.
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.
In 7 male cadavers the anatomical structure, thickness and tensile strength of the tunica albuginea of the penis, measured at specific locations, were determined. The tunica is composed of inner circular and outer longitudinal layers made up of collagen bundles. The outer layer appears to determine, to a large extent, the variation in thickness and strength of the tunica. The ventral groove (found between the 5 and 7 o’clock positions), which houses the corpus
spongiosum, lacks outer bundles and appears vulnerable to perforation. The thickness of the tunica measured at the 7, 9 and 11 o’clock positions was 0.8 +/- 0.1 mm, 1.2 +/- 0.2 mm and 2.2 +/- 0.4 mm, respectively. Differences in the thickness of the tunica at specific locations were statistically significant (all p < or = 0.018). Symmetrical measurements were nearly identical in a mirror image arrangement (3, 5 and 1 at the 9, 7 and 11 o’clock positions, respectively). The stress on the tunica at penetration (breaking point pressure) measured at the 7, 9 and 11 o’clock positions was 1.6 +/- 0.2 x 10(7) N/m.2, 3.0 +/- 0.3 x 10(7) N/m2 and 4.5 +/- 0.5 x 10(7) N/m.2, respectively. The strength and thickness of the tunica correlated in a statistically significant manner with location (r = 0.911 and p = 0.0001). The most vulnerable area is on the ventral aspect (which lacks the longitudinally directed outer layer bundles), where most prostheses tend to extrude. This finding supports our belief that prosthesis extrusion often has an anatomical basis and is not merely a phenomenon caused by infection or compression.