The testicles are egg shaped sperm producing organs, suspended outside of the body in a fleshy sac or pouch called the scrotum. They are suspended inside this sac by the spermatic cords which are made up of arteries, veins, nerves, lymphatics and the ejaculatory duct. The testes are located outside of the abdominal cavity in order to maintain the optimal temperature for sperm production, about 3 degrees Celsius cooler than the rest of the body. When the body is hot the testicles hang lower than when the body is cold, which explains why testes will retract in cool weather closer to the abdomen in order to maintain the correct temperature for sperm production. Production begins at puberty and continues right through until old age.
Each testis is encased in a rugged, fibrous white capsule and along its back border, the connecting tissues progressively thicken and lead into the organ forming a mass known as the mediastinum testis. From this mass, a thin divider of connective tissue, called septa, extend into the testis and forms about 275 lobules. A lobule has 1-4 coiled seminiferous tubules, each one of these can be up to 75 cm long when uncoiled. Between these tubules the interstitial compartments are located. These tubules travel around the back of the testes and unite to form a complex network of channels called the rete testis. The rete testis resides within the mediastinum testis and has several ducts that enclose a tube like structure known as the epididymis. The epididymis are seminiferous tubules that coil around the outer surface of the testis and are lined with a special tissue, called the germinal epithelium, that is responsible in producing the sex cells.
These tubules and compartments are where spermatogenesis (the production of gametes), and steroidogenesis (the production of male steroid hormones) take place. The compartments are separate but work closely together for the efficient production of sperm. The function of the testicles and these compartments are controlled and regulated by the hypothalamus and the pituitary gland.
The most important cells in the interstitial compartments are Leydig cells. These cells are responsible for the production of androgens or testosterone. Also located within these compartments are immune cells, lymph and blood vessels, nerves and connecting tissue. Inside the seminiferous compartment spermatogenesis occurs, and is about 80% of the total volume of each testicle. In an average adult male there would be approximately 350 + meters of seminiferous tubules in each testicle, therefore in both it would be a total of over 700 meters!
The process of spermatogenesis begins with the dividing of stem cells, and finishes with mature sperm formation. There are four stages involved in this process; a) Mitotic – the proliferation and dividing of germ cells (spermatogonia). b) Meiotic – the dividing of tetraploid germ cells that results in spermatids. c) spermatids transform into sperm (spermiogenesis). d) The releasing of sperm into the tubular lumen.
The structure and functioning of the testes is extremely complex, this brief article tries to explain the basics in a way that the ordinary person can understand and comprehend.