The testes or testicles are part of the male genitalia or sexual reproductive organ. It is a structure that is ovoid in shape and between four to six centimeters in length. These bilateral though not always symmetrical anatomical structures are the site of sperm production.
The testis are retroperitoneal from the time they are developed in the embryonic process to when they descend into their final adult position in the scrotum. The testicular tissue is comprised of two hundred to three hundred lobules that are separated by connective tissue septa. Each lobule contains between two and three seminiferous tubules that are coiled extremely tight and are approximately one meter in length when straight. It is here that the spermatozoa and sex hormones are produced. The tubules converge in the posterior region of the testis and the collective amount of product is released into the network of the rete testis.
The testes hang in suspension attached to the spermatic cord and are covered externally by the loose, wrinkly, pigmented skin known as the scrotum. Just inside the scrotum, there are three more distinguishable layers that protect the testicular tissue. The outermost layer is known as the tunica albuginea and is a tough fibrous capsule. The middle and innermost layers are actually one layer known as tunica vaginalis which is split into a visceral layer and a parietal layer. They are derived from the peritoneal outpocketing that occurs during embryonic development. The layers are separated by a serous fluid that allows testes to move in the scrotal sac. A posterior deficiency is apparent for the transmission of the epididymis and the blood vessels. The visceral layer is in the middle and it is a serous layer that covers the testes, epididymis and the distal part of the spermatic cord. The innermost layer is the parietal tunica vaginalis. The testicular artery is the main form of blood flow to the area and is drained through the pampiniform plexus. The lymph vessels ascend with the testicular vessels and drain into the lumbar nodes.
Cryptorchidism is a phenomenon based on a developmental malfunction which occurs when the testes fail to descend from their embryonic position inside the abdominal cavity into the scrotum. Even after surgical correction, this disorder is quite severe, seeing as it has been proven to be associated with testicular atrophy, sterility and a much higher risk of developing various germ cell tumors, in particular seminoma and embryonal carcinoma.