Testis, commonly referred to as testicle, is a mobile organ lying within the scrotum. It is an important component of both the male reproductive system and the endocrine system. The primary functions of testis are to produce sperm and androgens.
Appearance of testis:
Human beings commonly have one testis hanging lower than the other. More people have left lying lower than the right testicle. The upper pole of the testis is tilted slightly forward. Each testicle is surrounded by a tough fibrous capsule known as the tunica albuginea.
Size of testis:
In healthy European males, the average volume of each testicle is 18cm2. The average size after puberty measures to around 2 inches in length, 0.8 inches in breadth and 1.2 inches in height.
Internal structure of testis:
From the inners surface of the tunica albuginea, a series of fibrous septa extend towards the interior of the organ. These septa divide the testicle into several lobules. Within each lobule, there lay one to three coiled tubules known as seminiferous tubules. These tubules open into a network of channels called the rete testis. Small efferent ductules connect the rete testis to the upper end of the epididymis.
In summary the internal structure of testicle consists of the following components;
- A series of fibrous septa that divide the organ into lobules
- Seminiferous tubules those are present within each lobule
- A network of channels, the rete testis, into which the seminiferous tubules open
- Small efferent ductules, those connect the rete testis to epididymis
Blood supply of testis:
Blood supply of testis is distinct from the scotum, the pouch within which it lies.
Most of the blood supply of testis comes from paired testicular arteries, which arise directly from the abdominal aorta. They descend through the inguinal canal as part of the spermatic cord.
Testes also receive collateral blood supply from cremasteric artery and artery of the ductus deferens. The collateral supply is enough for testis to survive even if the paired testicular arteries are ligated.
Lymph drainage of testis:
As was the case with blood supply, the lymphatic drainage of testis is also different from the scrotum. The testicular lymph vessels follow the testicular arteries back to the para-aortic lymph nodes.
Temperature regulation of testis:
Normal spermatogenesis occurs only if the testes are at a temperature lower than the abdominal cavity. In the scrotum, they remain at temperature about 3 degrees Celsius lower than the abdominal temperature.
The control of testicular temperature and its regulation is not fully understood, however, it is known that the surface area of the scrotal skin can be changed reflexly by dartos and cremaster muscles. When the skin becomes thick, the testes get a warmer environment and vice versa.
It is also recognized that the Pampiniform plexus, together with the branches of the testicular arteries, assist in stabilizing the temperature by a countercurrent heat exchange mechanism.