The testicles (or male gonads) represent the two male sex glands. During foetal development they are located in the abdomen and usually descend into the scrotum (the sac that contains them) just before the birth. The male sex glands are not always the same size throughout life: they are small during childhood, increase in volume during puberty until they reach sexual maturity, only to suffer a setback in late physiological age.
What are the testicles?
The testicles are egg-shaped with a firm texture and represent the male sex glands. Once they reach sexual maturation, they reach a size of around 4-5 cm long, width of about 4 cm and a thickness of around 2.3 cm; Moreover, they weigh about 20 grams each. Although they seem quite symmetrical, generally the left testicle is placed lower than the right.
Each testicle is covered by firm, fibrous layers or tissue known as the tunica. The outer layer is referred to as tunica vaginalis, while the inner layer is called tunica albuginea.
Each testis is internally divided into lobules (about 250 per testis) in which are contained the seminiferous tubules, inside which the production of spermatozoa (spermatogenesis) occurs. The seminiferous tubules are initially twisted (convoluted tubules), but then assume a rectilinear conformation (rectilinear tubules) and flow together in the testicular network (or "rete testis"), formed by channels of varying amplitude. From the start of the testicular network there are efferent ducts that reach the epididymis, (little body stretched on the top-rear edge of the testicle) which is the section of the sperm ducts located between the efferent ducts of rete testis and the vas deferens (duct deputy transport of semen).
In the space that is formed between the convoluted tubules are compact cell clusters that form the interstitial Leydig gland. The nerves that innervate the testicles come from the spermatic plexus. The blood vessels are called spermatic vessels.
Furthermore, each testicle is held in the scrotum by spermatic cords. The spermatic cords are comprised of connective tissue and muscle. They also contain the vas deferens, blood vessels, lymph nodes and nerves. Lymph fluid flows through the vessels that are located in the spermatic cord and drains from the testicles into several groups of lymph nodes. These lymph nodes are referred to as the retroperitoneal lymph nodes.
What function do the testicles serve?
There are two functions performed by the testicles from puberty: an endocrine and exocrine function. The exocrine function consists of spermatogenesis, or the production of sperm, necessary for reproduction. However, this process can also be performed by only one testicle.
The endocrine function consists of the secretion of testosterone: the presence of this hormone in the male is indispensable, as well as for the induction of spermatogenesis, for the development of the so-called secondary sexual characteristics (increase in muscle mass, lowering of the tone of voice, increased body hair).
The exocrine function, or the process of sperm production, begins in the germ cells, which are located in the seminiferous tubules. The germ cells later mature into sperm cells. On the other hand, the endocrine function, or hormone production (testosterone) is performed with the help of stromal cells, which act as supportive cells within the testicle.
