Very few men (let alone women) know that in addition to the testicles, the scrotum also houses the epididymis. Yet these are particularly important for male fertility: this is where sperm mature and wait for their “assignment”.
What do the epididymis look like and what exactly do they do?
The epididymis (epididymis, parorchis), together with the penis and testicles, belong to the male sex organs. Together with the testicles, they sit in the scrotum. Like a “C”, they extend longitudinally down the back of the testicles from their upper end.
Each epididymis is about 5 cm long and contains inside it a strongly looped tube up to 6m long, the epididymal duct (Ductus epididymidis). The upper end, the head of the epididymis (caput epididymidis), is connected to the testis by many small ducts, the seminiferous tubules (ductuli efferentes).
The middle section of the epididymis is called the body (corpus epididymidis). At the lower end follows the tail of the epididymis (cauda epididymidis), which passes directly into the vas deferens. The vas deferens finally opens into the urethra at the level of the prostate. The entire epididymis is closely connected to the testes by connective tissue (mesepididymis).
The interior of the epididymal duct is lined with a tissue (cylinder epithelium) densely covered with small “cilia” (stereocilia). On the outside, contractile myofibroblasts (connective tissue cells that contract) are located at the head and body of the epididymis, and the tail is surrounded by smooth muscle cells. This allows the epididymal duct to contract and transport sperm onward.
What is the function of the epididymis?
The immature sperm cells from the testes enter the epididymis through the seminiferous tubules. Contact with the wall of the epididymal duct, the epididymal epithelium, is important for the subsequent motility of the sperm. The epithelium secretes glycoproteins, molecules of sugar and protein. These are taken up by the surface of the sperm cells.
Over the course of about 12 days, contraction of the myofibroblasts transports the sperm from the head over the body to the tail of the epididymis, where they are finally stored. When the smooth muscle of the epididymis tail contracts, the sperm are transported via the vas deferens to the urethra and finally released to the outside during ejaculation. Incidentally, the sperm cells only reach their final fertilization ability in the female genital tract.
The so-called capacitation, which is triggered by the estrogen in the female body, enables the sperm to penetrate the sheath of the female egg.
