Local course of spermatogenesis - the spermatogenesis wave
In examining a cross-section of a convoluted seminiferous tubule one notices that cells appear in groups having the same maturation stages. However, not all the spermatogenesis stages are found in a cross-section.
- Leptotene/zygotene of the
spermatocytes typ I - Pachytene of the
spermatocytes typ I - Young spermatids
- Older spermatids (sperm cells heads can be recognized)
- Sertoli's cells
- Spermatogonia
Various developmental stages in a light microscope cross-section through a convoluted seminiferous tubule
On the one hand, the reason for this appearance lies in the fact that the daughter cells, generated by each meiotic step, remain bound together by thin cytoplasmic bridges. Thus with each meiotic step the following generation is twice as large, until the cells have formed a relatively complex network. The result is that cells of the same development stages are seen there in groups. On the other hand, in addition, other spermatogenesis generations are wound around each other in spirals along the seminiferous tubule. This is why one meets with groupings of various generations in a tubule cross-section. Thus, it is highly improbable that all of the development stages will be seen in a single section at the same time.
This picture shows three waves of spermatogenesis generations.
As in the diagram, spermatogenesis waves move in spirals - like a corkscrew - towards the inner part of the lumen. Outside, on the edge of the tubule and at the beginning of the spiral, lie the spermatogonia; and, at the end of the spiral, the fully developed sperm cells are in the lumen. From the diagram, it can be seen that several differing generations can be found in a tubule cross-section. As time goes on, the wave of spermatogenesis is shifted towards the right (as seen here) in order to always newly begin again.