The testes are the primary male reproductive organs, playing a fundamental role in reproduction. These paired structures are responsible for two distinct yet interconnected functions: the generation of male gametes, known as sperm, and the synthesis of male sex hormones. Their coordinated operation is foundational to male fertility.
Where Testes Are Located
The testes reside within the scrotum, an external pouch of skin below the pelvic cavity. This external positioning is important, as it maintains the testes at a temperature 2 to 3 degrees Celsius lower than core body temperature. This cooler environment is required for optimal sperm production. Each testis measures 4 to 5 centimeters in length and 2.5 to 3 centimeters in width, with an oval shape. During fetal development, the testes descend from the abdominal cavity into the scrotum, a process completed before birth.
Inside the Testis
Each testis is encased by a fibrous capsule called the tunica albuginea, which provides support and protection. Extensions of this capsule, known as septa, project inward, dividing the testis into 250 to 300 compartments called lobules. Each lobule contains one to four highly convoluted tubes, the seminiferous tubules, which are the primary sites where sperm production occurs. The combined length of these tubules within a single testis can be several hundred meters if uncoiled. At the posterior side of the testis, the seminiferous tubules converge into a network of channels known as the rete testis, which collects sperm.
The Cell Powerhouses
Within the seminiferous tubules, two specialized cell types perform distinct yet complementary functions. Sertoli cells, also called nurse cells, are large, columnar cells that extend from the basement membrane to the lumen of the tubule. They provide support and nourishment to developing sperm, aiding their development. These cells also form the blood-testis barrier, a protective barrier that isolates developing sperm from the bloodstream, shielding them from immune responses. Scattered in the connective tissue space between the seminiferous tubules are Leydig cells, also known as interstitial cells. These cells are responsible for the production and secretion of male hormones, primarily testosterone. Testosterone is a steroid hormone that plays a comprehensive role in male reproductive health, influencing sperm production within the tubules and regulating the development of male secondary sexual characteristics. The activity of Leydig cells is regulated by luteinizing hormone (LH) from the pituitary gland.
The Sperm Pathway
Following formation within the seminiferous tubules, sperm move into the rete testis, a network of channels. From the rete testis, sperm pass into efferent ductules, which transport them out of the testis. These ductules lead into the epididymis, a long, coiled tube on the posterior aspect of each testis. The epididymis serves as a site for sperm maturation, where they gain motility and the capacity to fertilize an egg, and also stores mature sperm. From the epididymis, sperm are propelled into the vas deferens, a muscular tube ascending into the pelvic cavity, carrying sperm towards the ejaculatory duct for ejaculation.