Semen analysis is a routine test performed to determine sperm count, motility and morphology. It involves observing a semen sample under a microscope to evaluate the number of sperm present and their shape.
This is best done using a differential interference contrast (DIC) microscope. DIC is less likely to damage the samples and allows for clear viewing without staining, which can affect the results.
The Head
Sperm cells, also called gametes, are male sex cells that contain 23 chromosomes and are produced in the testicular organ of male human beings and other mammals. Each sperm has a head piece that contains the paternal genetic material, a flagella tail that propels it, and a middle piece with mitochondria that supplies ATP (the energy of life).
The head of a normal sperm is smooth and oval. It is surrounded by an outer layer of acrosomal region, which has the shape of a cap and includes polysaccharides such as mannose, hexosamine, galactose, and others. The acrosome helps sperm identify the female egg and allows it to drill through the egg’s thick membrane, which aids fertilization.
A healthy sperm head has a broad base and tapered apex, which makes it look a bit like an egg. It also contains a nucleus that contains the DNA needed to create a new organism.
In the laboratory, sperm samples are stained to make them easier to see under a microscope. However, staining can damage or kill living organisms and cells. For that reason, many scientists use phase contrast microscopy to observe sperm cells without staining.
Other methods include Papanicolaou staining and a technique called seminograms. The sperm analysis provides information about the number of sperm per milliliter of semen, sperm concentration, motility and morphology.
The Neck
For sperm to reach the egg for fertilization, they need to be able to swim. Unfortunately, about half don’t make it — they’re too slow or too erratic. One way to evaluate sperm motility is to use a specialized semen microscope. A good sperm microscope is one with a wide field of view, a high magnification (usually 400x or more), and a digital camera.
The neck of a sperm cell is the thin region connecting the head and the tail. The sperm’s neck contains a variety of primary amines, including cadaverine and spermine, that are responsible for the cell’s alkaline nature. These compounds protect the sperm from degradation by acidic vaginal fluids and ensure successful fertilization.
Sperm cells also contain the acrosome, an organelle that initiates the fertilization process by releasing lysosomal enzymes to break down the egg’s thick membrane. The acrosome also contains the genetic material that will become part of the fertilized embryo.
Sperm have a lot going for them, despite the fact that they are a bit erratic. Just like salmon swimming upstream, they have a hard time swimming in a straight line. And if you’ve ever had a look at some of the deformed heads and tails that get ejaculated out of the human body, you know what I mean: huge heads, pinheads, coiled tails — they’re all over the place.
The Centerpiece
The center of a sperm is called the acrosome, which contains powerful chemicals that eat through an egg’s thick membrane and release its genetic cargo. The acrosome also helps sperm navigate through the vaginal canal and identify its target female gamete, a process known as chemotaxis.
The acrosome is also responsible for giving semen its distinctive smell: a mixture of sulfur and ammonia, which is probably why it’s often mistaken for rotting cabbage. Semen also contains an alkaline liquid called triglyceride, which gives it its characteristic red color.
A microscope is essential for examining sperm, as it can help to see the tiny wrigglers’ details in more detail than is possible with the naked eye. For the best results, it’s recommended to use a microscope that uses phase contrast microscopy. This technique turns the tiny shifts in light passing through a sample into visible brightness variations, allowing you to view samples at higher magnification without using excessive illumination.
A basic sperm/semen microscope can be purchased at Microscope World for under $50, and it will provide you with sufficient magnification to see the sperm in detail. We recommend the HS-1M, which offers 400x magnification and has cool LED lighting that won’t heat up your sperm samples (so you can still see their movement). It also has coarse and fine focusing for more precision.
The Tail
The tail of the sperm is long and thin. It is composed of a central axoneme and nine peripheral doublets microtubules, all surrounded by a dense outer fibre sheath. The tail can be seen by a microscope with an electron detector.
A sperm sample is transparent, so it is often stained to make it easier to see under the microscope. The staining process, however, may kill or damage the cell. Since motility evaluation requires a healthy cell, many labs prefer to use phase contrast microscopes rather than staining for this purpose.
In addition to the standard optical microscope, labs also often have an electron microscope to detect sperm. A good electron microscopy lab will be able to scan a slide with a sperm sample and automatically analyze the image. This is an excellent way to get a fast and accurate analysis of motility and sperm quality.
Unlike a normal light microscope, an electron microscope can easily reveal sperm clumps in seminiferous tubules or epididymal ducts. It can also show a clear view of the stereocilia in the lining of the epididymal ducts. These are the cells that collect sperm from the testes. The sperm then flows down the epididymal duct and is expelled from the body by a urethra.
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