Neurovascular Supply of the Testes
Supplying target organs with nutrient rich oxygenated blood and removing its metabolic waste is integral for the survival of the cells of that structure. Additionally, most organs are dependent on neuronal signalling in order to carry out specific tasks. With reference to the testes, there is a relatively simple, bilateral neurovascular network that supplies each of the spherical reproductive organs.
In addition to providing oxygen, nutrients and removing waste from the area, the rich vascular supply of the testes has other functions since the organs have temperature specific functionality, and they also function as endocrine glands as well as reproductive organs. This article will highlight the course of the neurovasculature of the testes, their lymphatic drainage in addition to certain physiological functions that are executed by the vascular structures.
The testicular arteries are a bilateral pair of vascular structures that branch directly from the abdominal aorta. They arise from the anterolateral surface of the massive artery caudal to the renal vessels, at the level of the base of the L1-L2 vertebra. The right testicular artery crosses the inferior vena cava anteriorly and travels inferolaterally, medial to the right testicular vein and the proximal part of the right ureter. On the body of psoas major, the artery also crosses the ureter anteriorly and continues its inferior course.
On the left hand side, the left testicular artery travels medial to the testicular vein. However, it has a more vertical course proximally, compared to that of the right testicular artery. Similarly, it also crosses the left ureter anteriorly. Both the left and right testicular arteries course laterally to the common and external iliac vessels. They only cross the external iliac vessels as they enter the inguinal canal via the deep inguinal ring (at which point the external iliac vessels become the femoral vessels). Within the canal, they course lateral to the vas (ductus) deferens and its artery.
It should be noted that the testicular artery, once in the scrotum, gives a branch to the epididymis before bifurcating into lateral and medial branches. These two branches further divide to directly perforate the substance of the organ. Additionally, there are three notable arterial anastomotic connections formed with the testicular artery. The cremasteric arteries each arise from the anteromedial side of their corresponding inferior epigastric artery (branch of external iliac artery) and forms an anastomosis with the testicular artery as it passes through the spermatic cord (in the inguinal canal). The artery of the ductus deferens arises from the inferior vesical artery, which is given off by the anterior division of the internal iliac artery. It also forms an anastomosis with the testicular artery.
A rich network of interconnecting veins form a venous plexus around the testicular artery. This network, known as the pampiniform plexus, travels cranially with colder, deoxygenated, nutrient poor blood.
Once the plexus leaves the scrotum and enters the spermatic cord, its branches begin to coalesce until there are four branches. At the deep inguinal ring, on either side of the testicular artery, two branches fuse. Therefore, two valvular testicular veins travel alongside each testicular artery towards their drainage points. Shortly thereafter, the two veins combine to form a single testicular vein, which travels laterally alongside the testicular artery over the anterior surface of the psoas muscles.
About the level of the L3 vertebra, each testicular vein crosses its corresponding ureter on the anterior surface of the psoas muscles. The left testicular vein then takes an almost vertical course – travelling now between the testicular artery on its medial side and the ureter on its lateral side – to pierce the left renal vein. However, on the right hand side, the right testicular vein travels almost vertically, then obliquely (also with the ureter lateral and the testicular artery medial) before directly draining to the inferior vena cava.
The T10 spinal segment provides the sympathetic nerve fibers that innervate the testes. They travel by way of the lesser splanchnic nerves and synapse at the celiac ganglion. The post-ganglionic fibers then follow the testicular artery along its course to its point of innervation. Sensory root fibers also take a similar course and pass information via the dorsal root ganglion cells of the T10 segment. Furthermore, genital branch (L2) of the genitofemoral nerve (L1, L2) of the lumbar plexus provides sensory innervation to the tunica vaginalis of the testes.
Of the structures comprising the male external genitalia, the testes are the only ones that do not drain to the inguinal lymph nodes. Its lymphatics course along the route of the testicular vessels to reach the para-aortic lymph nodes at the level of the L2 vertebra.
Physiology of the Vascular Supply
It has been noted that deviation above or below the optimal thermal range for the testes can disrupt spermatogenesis (process of forming new sperm cells). It is therefore a common belief that the suspension of the testes in the scrotum, outside the body cavity, facilitates adequate thermoregulation. In addition to being outside the body cavity, further thermoregulation of the testes is achieved by the action of the pampiniform plexus. The plexus wraps around the testicular artery in the scrotum. The blood in the testicular artery is warmer than the blood in the pampiniform plexus. Conveniently, a countercurrent thermal exchange between the contents of the vessels occur such that the blood leaving the testes in the pampiniform plexus cools the blood going to the testes in the testicular artery.
For completion, the cremasteric reflex also assist in thermoregulation of the testes. When the external temperature is too low, the cremaster muscles (innervated by motor fibers of the genital branch of the genitofemoral nerve) contract. This action pulls the testes closer to the body, where they can be warmed.
Finally, in addition to being reproductive organs, the testes are also endocrine glands. Interstitial Leydig cells of the testes produce and secrete testosterone. The testosterone has effects on local testicular tissue, as well as it participates in a negative feedback mechanism that regulates the release of luteinizing hormone (LH) from the adenohypophysis (anterior pituitary gland).