In biology, morphology refers to the study of the structure and form, to the characteristics of organisms and their features. Morphology will observe the outward appearance of the organisms, meaning their structure, shape, pattern and color, but it is also interested in form of the internal parts of the organisms, such as organs or bones. Morphology can also be defined in opposition with physiology, which is only interested in the functions of organisms. Sperm morphology is part of the initial evaluations that are done in order to investigate sperm quality, or cases of subfertility and infertility.
The actual tasks that are accomplished during sperm morphology are that the size and shape of the sperm’s head, midpiece and tail are observed and examined. Sometimes, an evaluation of the integrity of the acrosome and sperm membranes is done, for a more complete diagnosis. Sperm shapes and sizes differ from species to species, with human and bull sperm being similar with its paddle-shaped heads. Other animals, like rodents, have hook-shaped heads, whereas chickens have spindle-shaped heads.
When a sperm morphology exam is done, the results are presented with the normal percentage. It is not unusual that a part of the sperm count be considered morphologically abnormal, but larger percentages may result in infertility, or decreased fertility. The morphology exam will show which parts of the sperm are abnormal, the heads, midpieces or tails; sometimes, more than one part of the sperm is morphologically abnormal. The morphology exam of the sperm will also indicate whether there are primary or secondary effects. Primary effects are more serious, because that’s when the sperm is deformed while still inside the semeniferous epithelium of the testicles. Secondary effects are less grave, because they represent sperm which has become abnormal through its navigation in the epididymis or by misuse after ejaculation.
Some of the more common morphology abnormalities encountered in sperm are the double-headed sperm, the misshapen head along with four normal sperm, sperm with elongated head, pyriform – meaning pear-shaped – head and bent sperm with abnormal midpiece, misshapen head and proximal droplet, distal droplet, detached head, bent midpiece or tail, coiled tail and coiled midpiece and/or tail in one sperm with proximal droplet in another. When preparing semen specimens for a morphological examination, some staining techniques are used; the most common of these is the nigrosin-eosin stain because it is the easiest to use and the most efficient. This is how sperm morphology is examined, and it is a very important aspect when investigating possible fertility.