A single spermatozoon is a remarkable achievement of nature. This is the smallest and most physically active cell in the human body and is highly specialised for one simple function – fertilisation of the egg. To achieve this, the sperm have adapted to eliminate all unnecessary baggage. The sperm consists of a tail connected to a biological engine which provides huge energy supplies for the long journey to the egg. At the head of the sperm is tiny bag-like structure called the acrosome, which detonates on contact, shedding enzymes which cut through the outer layers of the egg allowing the sperm access to the surface, where it binds and then enters initiating fertilisation. This must surely be one of the most beautiful functions in all biology.
Between the acrosome at the head and the engine at the tail is the all-important payload of the sperm, the male DNA. The DNA occupies most of the area of the sperm head, there is very little else as the usual cellular cytoplasm or cellular machinery are absent, the embryo derives all these things from the egg. This is why the egg is the largest cell in the human, full of everything to get the embryo off to a good start. All the sperm brings to the party is its crucial DNA contribution. The sperm DNA itself is highly packaged into a very small space, which also protects it against damage.
Sperm start off as cells called spermatogonia in the testes. They start the maturation process through mitosis to become spermatocytes. These then split in two by meiosis and then two again to form spermatids, which in turn mature into spermatozoa (sperm cells). The process starts off in the testes and the maturation finishes off in the epidydimus where the sperm is stored before being passed on to the vas deferens. The epidydimus is a coiled tube about 250 inches long and the vas deferens adds another 12 inches on to the journey. The whole process takes 2 to three months to complete and any problem along the way can cause fertility issues. When a man produces a sample for testing or treatment at a fertility clinic, he usually does this in a production room next to the lab. Home production is possible in extreme cases although for quality reasons we prefer the sample is produced at the lab.
What If There Are No Sperm At All?
Even situations where there are no sperm in the ejaculate at all are not hopeless. A complete absence of sperm is called azoospermia and if this appears to be the case the first thing the seminologist will do is to centrifuge the semen sample, so that any cells or particulate material settle as a pellet at the bottom of the tube. The pellet is then examined microscopically, if there are any sperm in the sample then this is where they will be. Finding a single sperm here will open the door to ICSI.
Assuming all this is carried out and still no sperm can be found, an important possibility still remains. One of the main causes of azoospermia is congenital absence of the vas deferens. The vas deferens is a structure that connects the testis to the ejaculatory ducts. In around 1 – 2% of men with fertility problems this structure is missing. These men usually produce normal sperm but they do not reach the ejaculatory ducts where they are mixed with secretions from the seminal vesicles and prostate gland at the moment of ejaculation. So the semen appears normal except for a complete absence of sperm. In fact any blockage to the normal path of the sperm whether congenital or acquired can be resolved by extracting sperm from the testes via a fine needle, followed by ICSI.