Evaluaciones Internas y Externas

Arterial blood supply of the testis occurs predominantly via the testicular artery, which arises directly from the abdominal aorta and descends through the inguinal canal reflecting testicular descend, whereas the scrotum and the rest of the external genitalia are supplied by the internal pudendal artery, a branch of the internal iliac artery. In addition to the major blood supply by the testicular artery, the testis may have collateral blood supply as the distal part of the testicular artery often anastomoses with the cremasteric artery (a branch of the inferior epigastric artery) and the deferential artery (a branch of the inferior vesical artery, which is a branch of the internal iliac artery). After reaching the testis near its upper pole, the testicular artery runs down the epididymal margin of the organ just under the capsule in a reasonably straight course to the distal part of the testis. Soon after rounding the distal pole it forms several branches which aspire to free margin of the testis. The terminal branches of the testicular artery eventually enter a vascular network situated in the deeper layer of the tunica albuginea formed by winding arteries, with the exception of the posterior part of the testis on both sides of the testicular artery, which are not covered with these vessels (Polguj et al. 2011). The arterial supply of the testicular parenchyma follows the lobular structure in that centripetal arteries arising from the superficial vascular network enter the testicular septa and run in a relatively straight course to near the mediastinum, where they form coils and turn back as centrifugal (recurrent) arteries. On their

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way towards the testicular surface within the lobules, the centrifugal arteries give rise to segmental arteries, which originate at a regular distance from each other, branch within the interstitial tissue and finally give rise to a capillary network and the venous system (Setchell &

Main 1975, Myrén & Einer-Jensen 1992).

The venules draining the interstitial tissue empty into intralobular veins, which empty into veins in the septa (Setchell & Main 1975, Myrén & Einer-Jensen 1992). The venous blood flow in the septa exhibits considerable differences between mammalian species. In the boar, most of the veins run centrifugally towards the surface to empty into a subalbugineal plexus, which finally join an intra albugineal plexus and superficial veins running to the proximal pole of the testis, which final drain into branches of the pampiniform plexus (Setchell & Main 1975, Myrén

& Einer-Jensen 1992).

Despite a significant number of studies on the fine structure of testicular lymphatic spaces and the walls of lymphatic vessels, information on the gross architecture of the lymphatic system in the testis is sparse and in part conflicting. Moreover, information so far available indicates significant species specific and individual differences. In general, lymphatic vessels may reach the testicular surface via the testicular septa, which empty into a superficial plexus, or via the rete testis. Superficial collecting lymph vessels originate from the proximal extremity and the epididymal border of the testis. These lymph vessels may ascend along the testicular artery thereby reducing their number (Itoh et al. 1998, Heinzelbecker et al. 2014). However, as shown in the rabbit, testicular efferent lymphatic vessels may not only course along the testicular artery, but to a minor extent also along the ductus deferens and/or cremasteric artery (Heinzelbecker et al. 2014).

2.4.2 The vascular and lymph system of the epididymis

The angio-architecture of the epididymis is in part species specific. However, basically epididymis blood supply is derived from two sources: the testicular artery and the deferential artery. In the boar two branches (rami epididymales) origin from the testicular artery immediately proximally to or after the beginning of its highly convoluted part in the vascular cone. Soon after their origin from the testicular artery, the epididymal branches form a widely ramified network, which supplies predominantly the epididymal head and the proximal body.

However, some arteries originating from this network run to the distal body and the proximal tail to supply also these parts of the epididymis. From the deferential artery epididymal branches originate already proximally of the vascular cone and run to the hind part of the epididymis

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together with branches of the rami epididymales. Only the hind part of the epididymal tail is exclusively dependent on supply from the deferential artery. Anastomoses between branches from the testicular artery and the deferential artery may already occur within the region of the vascular cone. The venous blood vessels follow the arteries (Stoffel et al. 1990).

No specific information was found concerning the architecture of the lymphatic system in the porcine epididymis. In rats it has been described that the epididymis is drained by lymphatics emerging separately from different regions of the head, body and the tail and which converge to form a single vessel draining into the main testicular trunk. The pattern of lymphatic drainage in general is very similar to that of the arterial blood supply. Anastomoses occur at various levels between lymphatics draining the testis and the epididymis (Pérez-Clavier et al. 1982).

2.4.3 Architecture of the vascular cone of the spermatic cord

The testicular vascular cone is a specialized anatomical structure located in the distal part of the spermatic cord which is formed mainly by a highly sinuous and coiled section of the testicular artery juxtaposed between fine networks of testicular veins that form the pampiniform plexus.

Its main physiological role is the heat transfer between the warm arterial blood and the cool venous blood flowing in opposite directions within adjacent vessels occurring through a counter-current mechanism, as maintenance of testicular temperature some centigrades below body temperature is essential for normal spermatogenesis in most mammalian species. Detailed information on the vascular architecture in the boar spermatic cord is available from a study by using corrosion casts. In sexually mature boars the spermatic cord is about 17-20 cm in length.

In its upper fifth part, the testicular artery is relatively straight, whereas in the remaining distal part it is extensively convoluted. During the upper straight part of the testicular artery and the first 5-8 loops numerous thin branches arise forming a network for the arterial supply of the pampiniform plexus and the epididymis (Böttcher & Lange 1987, Rerkamnuaychoke et al.

1990, Stoffel et al. 1990; see also section “vascularization of the epididymis” (2.4.2))

The convoluted part consists of retrograde and spiraled loops of which the diameter steadily decreases towards the upper pole of the testis. Thus, the convoluted part has the form of a cone with the tip directed towards the testis. Despite the high degree of convolution and retrograde looping, a bifurcation was not found. The convoluted part is covered by venous plexus. The layers of veins covering the artery vary in number according to the distance of the artery from the surface of the vascular cone. Parts of the artery running close to the surface of the cord are covered by only one layer of veins. In the deeper part of the cord, there are at least three venous

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layers between its loops (Rerkamnuaychoke et al. 1990). After passage of the pampiniform plexus, the testicular artery penetrates the tunica albuginea near the proximal (cranial) testicular pole and runs under the epididymis and the tunica albuginea towards the caudal testicular pole (Böttcher & Lange 1987; see also section “vascularization of the epididymis” (2.4.2)).

The convoluted part of the testicular artery is embedded in the pampiniform plexus. This complex venous network emerges mainly from the back of the testis with additional tributaries from the epididymis (Heinze & Ptak 1976). It is composed of different types of veins characterized by different luminal diameter and structure of the vessel wall. The large type I veins form a network on the most outer surface of the spermatic cord. The medium-sized type II veins run as a single layer of anastomosing veins along the testicular artery. The type III veins, also classified as medium-sized, form networks of several layers between type II venous networks; anastomosing type II and III veins form the great part of the pampiniform plexus.

The small type IV veins arise from type II and III veins and form networks between the larger veins or between larger veins and the testicular artery. As they exhibit a thin fenestrated epithelium and may deeply penetrate into the media of the testicular artery, arterio-venous exchange may be efficient despite the thick arterial media.

In addition to its function as a heat exchanger, the testicular vascular cone has also been suggested to act as a countercurrent mechanism of hormone transfer, especially for maintaining a high concentration of testosterone in the testis. In addition to passive diffusion, a transfer between the testicular artery and the pampiniform plexus has been suggested to occur via arterio-venous anastomoses (Einer-Jensen & Hunter 2005). It has been described in different species including bovine (Amann & Ganjam 1976), human (Bayard et al. 1975), rhesus monkey (Dierschke et al. 1975), rams (Noordhuizen-Stassen et al. 1985) that the concentration of testosterone in the testicular artery by side of pampiniform plexus is higher than that in the systemic circulation. However, as the difference was generally low, the physiological relevance of these observations is unclear.